Cambridge IGCSETM
Computer Science
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Computer Science syllabuses (0478/0984). The series focuses on developing
important computer science skills relevant to real-world applications.
SB
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Computer Science
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ISBN 978-981-4941-59-4
Greg Shilton
Megha Goel
9 789814 941594
C01(S)IGCSECS_SB_Cover.indd All Pages
12/5/21 11:11 AM
Cambridge
IGCSE
TM
Computer Science
Greg Shilton
Megha Goel
SB CS PP.indb 1
STUDENT’S
BOOK
14.5.21. 14:13
© 2021 Marshall Cavendish Education Pte Ltd
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Chapter 1 p.1 Futuristic technology concept, Mixed media, Innovations data systems
connecting people and robots devices. AI, Artificial Intelligence, Robotic hand on
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visualisation in simple black and white monochrome style. Voice icon, vector, ©
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com; p.62 Young african male programmer writing program code sitting at the
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dreamstime.com; p.77 Credit or debit cards. Smart chip © Buradaki dreamstime.com;
p.78 Man open the door with NFC tag © Szabolcs Stieber dreamstime.com; p. 78
male using a password generator to perform online banking. Security token for
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Bitcoin symbol in flat design. stock illustration © iNueng istockphoto.com; Chapter 6
p.83 Close-up Of A Man’s Hand Using Smart Home Application On Mobile Phone At
Home © Andriy Popov 123rf.com; p.84 Round temperature sensor on the hot water
pipe © Denis Shipunov dreamstime.com; p.84 Microprocessor with motherboard
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stock photo © Maudib istockphoto.com, p.89 People examining economic statistic.
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navigation concept © scanrail istockphoto.com; p.89 Car diagnostic concept Close up
of laptop with OBD2 wireless scanner and retro car on gray gradient background 3d
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p.89 Beautiful butterfly Tailed jay, Graphium agamemnon, in tropical forest © Jag_cz
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entering safe code to unlock the door © stockyimages 123rf.com; p.149 Three happy
friends planning a travel on lineThree happy friends sharing on line content with
multiple devices sitting on a sofa at home Happy woman sitting on sofa and using
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guide sitting on a sofa at home © Antonio Guillem 123rf.com; p.158 Young teen girl
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14.5.21. 14:13
This book is designed to help you build your knowledge and understanding of essential Computer Science concepts. It will
also enable you to appreciate the application of Computer Science in your everyday life. This Student’s Book is part of the
Marshall Cavendish Education suite of resources that will support you as you follow the Cambridge IGCSETM and IGCSE (9-1)
Computer Science syllabuses (0478/0984) and prepare for your examinations.
Chapter opener
introduces the topic and
CHAPTER
key learning goals.
4
Software
COMPUTER SCIENCE WATCH*
makes learning ‘come alive’. The videos can be launched from
a smartphone or a tablet by scanning a page using the MCE
Cambridge IGCSE App.
COMPUTER SCIENCE WATCH
Scan the page to watch a clip on
the differences between system and
application software.
Please refer to www.mceapps.com for user guide and further
information.
*As the Watch videos are authentic and therefore reflect real-life
situations, they might in some instances contain content that is beyond
the scope of this syllabus. Always refer to the appropriate syllabus
document for the year of your examination to confirm the details and for
more information. The syllabus document is available on the Cambridge
International website at www.cambridgeinternational.org.
Before watching discuss what you expect
to see or hear.
QUESTIONS
• What is the link between hardware and
software?
• How is software essential to the operation
of a computer?
• How do humans use software to interact
with computing devices?
At the end of this chapter, you will be able to:
understand the difference between system software and application
software
• What is programming and how do pieces
of software begin their existence?
define the role and basic functions of an operating system
identify the hardware, firmware and operating systems that are used
to run applications software
Content in this feature has not been through the Cambridge
Assessment International Education endorsement process.
define the role and operation of interrupts
identify the difference between a high-level language and a low-level
language
understand the advantages and disadvantages of each type of
language
define the two types of translator: compilers and interpreters
identify the advantages and disadvantages of each type of translator
understand what an integrated development environment is used for,
including its common functions
QUESTIONS
59
IGCSE_CS_TB_Chapter_4.indd 59
assess your prior knowledge on the topic.
13.5.21. 16:32
Chapter 10
DEFINITION
explains key terms used
in Computer Science.
DEFINITION
Logic gates: the basic
units of a digit circuit
that control the flow of
electronic signals.
. Logic Gates
Logic gates are the basic building units of any digital circuit. Today, these circuits are used in almost
every computer system. From elevators to washing machines, logic gates are used all around you.
WORD ALERT
Words commonly associated
with the topic are highlighted
in red and explained in a
simpler way. This also helps
you to be more familiar with
the words and be confident in
using them.
Digital circuit used to open electronic door.
WORD ALERT
Combination: a joining
of different parts or
qualities.
There are a number of different types of logic gate, with different logic rules. The combination
of several logic gates forms a circuit, which allows for the design and performance in modern
computers. The gates receive binary data, apply a Boolean operation and then output a binary result.
Arithmetic: use of
numbers to calculate an
outcome.
Boolean Operations
Equivalent: the same or
equal meaning.
HELPFUL NOTES
LINK
Be careful not to confuse
the Boolean operator ‘+’
with ‘+’ , which means
‘plus’ in normal maths.
leads you to exercises in
the Workbook for further
practice.
SB CS PP.indb 4
The word ‘Boolean’ comes from Boolean algebra, which is the basis of computer arithmetic and
especially logic gates. There are only two Boolean values: true and false. They have equivalents in
normal language and in binary notation.
Boolean expressions can compare data of any type as long as both parts of the expression have the
same data. In computer science, Boolean expressions can be used in programming and produce
Boolean values when evaluated. Boolean values are either true or false:
Boolean value
Binary value
True

On
Synonyms
Yes
Positive
False

Off
No
Negative
There are also three logical operators: NOT, AND and OR. The Boolean operators for these are AND ‘•’,
OR ‘+’, and NOT ‘ ’, which is written above the letter.
Ā means NOT A.
A • B means A AND B.
A + B means A OR B.
Logic gates use both Boolean values and operators.
142
iv
This chapter will explore the types and functions of common logic gates.
IGCSE_CS_TB_Chapter_10.indd 142
Logic Gates and Circuits
13.5.21. 16:32
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Chapter 2
ENRICHMENT
This type of data transmission occurs when a computer or device is connected to another computer
or device using a single data channel. Data is transmitted one bit at a time, sequentially, down
the channel.
ENRICHMENT
promotes deeper thought
by: offering snippets of
information to supplement
your knowledge; providing
activities which help
reinforce learning; or posing
challenging questions to
encourage you to apply
the concepts learnt to
various contexts.
An example of this type of data transmission occurs when a computer is connected directly to a modem.
Can you find out when
serial and parallel ports
were no longer included
in computers? What
replaced them and why?
One of the advantages of using a serial transmission method is that it is very reliable for transferring
data over longer distances, although sometimes it is not the most practical. There are also much
fewer errors in serial transmission, as bits are sent one at a time, and only one single channel is
required to achieve this transmission. Thus, this is a lower cost method of transmitting data.
The disadvantage of a serial transmission is that transmission speeds can be slow as only one
channel is being used to transfer data.
Parallel Data Transmission
Computer
Figure . Parallel transmission.
REFLECT
Printer
Bits
(Multiple)
Parallel data transmission is where multiple bits of data are sent at the same time along different
channels in the same cabling.
Most modern printers
now are connected to
computers using network
cables and data is
transmitted much faster
this way.
An example of this type of data transmission is where a computer is connected directly to a printer.
The advantages of this type of transmission is that faster data transmission takes place because of the
multiple channels being used. The disadvantages are that this type of transmission is more expensive
and synchronisation errors can occur due to the separation of data across different channels.
Input
also leads you to exercises
in the Workbook for further
practice.
Computer
stimulates you to be aware of
your own thought processes
and explore different ways of
solving problems.
Unidirectional
Figure . Simplex transmission.
QUICK CHECK
LINK
WB
Simplex Data Transmission
REFLECT
Simplex transmission is a one-directional (or unidirectional) mode of data transmission. The data will
only go one way, and the receiver of the data does not send any data back to the sender.
What other devices
can you think of that
use unidirectional data
transmission?
An example of this type of transmission occurs between a keyboard and a monitor. The keyboard
sends input data to be displayed on a monitor, but the monitor does not send any data back to the
keyboard.
The advantage of simplex transmission is that the process can use the full bandwidth of the
channel. The disadvantage of this transmission type is that it is not possible to engage in two-way
transmission using this method, and most forms of communication rely on this to be successful. Activity
1
24
Data Transmission
2
Chapter 10
Now do the same for this situation. You can skip some steps if you don’t need them.
Tip: the circuits are normally on so something needs to happen if they go off.
• An alarm makes no warning sound if the door is closed and the window is closed. There are
hidden switches on the door and window through which a current is constantly passing. If
someone opens the door or window, the alarm sounds.
Name the logic gates represented by these truth tables:
IGCSE_CS_TB_Chapter_2.indd 24
QUICK CHECK
Write the Boolean algebra
expression for NAND,
NOR, XOR.
13.5.21. 16:33
Inputs
a
Worked Example
demonstrates how to solve
problems by applying
concepts learnt.
A



Output
B





Inputs
b
X




WB
Output
A



B



X






LINK
Consolidate your
understanding by
completing the Exercises
1-2 from pages 123-129
in the Workbook.
Chapter 10
Worked Example
We use Boolean logic all the time. Look at this situation using Boolean operators:
You have decided that you will do extra study if you are falling behind at school. You also decide
that you will do extra study even when you are not behind if your friend asks you to study
together. Express this using Boolean operators.
Solution
To express this formally and logically we need two pieces of information to make our decision
and another piece to represent the result of the decision. We can name our information like this:
WORD ALERT
Formally: officially /
explicitly.
Information needed to make decision
(behind at school) = TRUE if fall behind. If not, FALSE.
(friend asks you to study) = TRUE if friend asks you to study. If not, FALSE.
Result
(do extra study) = TRUE if we decide to do extra study. If not, FALSE.
Our logical expression is then:
(do extra study) = (behind at school) OR (NOT (behind at school)) AND (friend asks you to study)
This expression uses the three Boolean operators: NOT, AND, OR.
Activity
1
2
Activity gives you
opportunities to
apply what you
have learnt and
assess what you
know.
Write a logical expression like the example above for this given scenario.
There are two methods of getting to your part time job on time. You can get the bus but only if
you wake up before .am. If you wake up after this time, you will need to ask your parents to
take you in the car. If you wake up before .am but your parents offer to take you, then you will
always say yes as it is easier.
Draw the Boolean algebra symbols for the following:
a) A NOT B
b) A AND B
c) A OR B
Logic Gates and Circuits
IGCSE_CS_TB_Chapter_10.indd 149
149
13.5.21. 16:32
HELPFUL NOTES
Types of Logic Gate
There are three basic types of logic gate that will be examined in this chapter: NOT, AND and OR.
NOT
AND
OR
WORD ALERT
The left side of the logic gate is referred to as the input and the right side as the output.
We can use a truth table to show the function of the logic gate. Each of the logic gates has a different
truth table. These truth tables display all possible input combinations and the correct output.
Logic Gates and Circuits
IGCSE_CS_TB_Chapter_10.indd 143
SB CS PP.indb 5
In all logic gates except
the NOT gate, there are
two inputs. The inputs or
outputs have two possible
states: a value of 1 or a
value of 0.
Referred: denoted /
identified.
HELPFUL NOTES
supports your learning
by providing tips and
highlighting important notes
that you need to be aware of.
143
13.5.21. 16:32
v
14.5.21. 14:13
Chapter 10
Here is the truth table for the OR gate above:
Inputs
A




REFLECT
Output
B




If someone asks you, ‘Do
you want a soda or some
water?’, you can’t answer
‘Both, please’. If you could
have both that would be
an inclusive use of OR. Is
the OR gate inclusive or
exclusive?
X




Logic notation: X = A OR B
Boolean algebra: X = A + B
Out of the four possible output states, the only time output X will be  is when both the inputs
A and B are .
An inclusive OR is what is shown in the truth table if either A or B is True, or if both are True, then the
statement value is True.
An exclusive OR only returns True when A OR B is True only.
Worked Example
WORD ALERT
A security light outside a house comes on after .pm or if it is dark. Make a table showing
the operation in normal language with corresponding Boolean and binary values. Make the
resulting truth table and choose the logic gate that will make this happen.
QUICK CHECK
Condition: the state of
something in relation to
its appearance, quality or
working order.
Solution
We have to state the conditions under which the light will come on:
if it is after .pm
if it is dark
serves as a checkpoint to check
your understanding of concepts.
Rate your confidence level
in your answer by drawing a
pointer on the confidence meter.
Then we convert these into the Boolean values ‘True’ and ‘False’:
it is after .pm = Yes/True/Positive
if it is dark = Yes/True/Positive
QUICK CHECK
Next we add the binary values:
it is after .pm
it is dark
Let’s Map It provides
a visual summary of
the concepts covered
to help you integrate
your learning and form
connections between
different concepts.
Yes
Yes
True
True
Positive
Positive


In all logic gates except
the NOT gate, there are
two inputs. The inputs or
outputs have two possible
states. What are they?
Then we make the truth table. The inputs are ‘it is after .pm and ‘it is dark’:
Inputs
it is after .pm
it is dark
The light coming on is the output:
Inputs
it is after .pm
Output
it is dark
the light comes on
Remember that the light will come on if either of the conditions is true:
Inputs
it is after .pm
No
No
Yes
Yes
Let’s Review offers questions
to test your understanding
and gives you consolidated
practice.
Output
it is dark
No
Yes
No
Yes
the light comes on
No
Yes
Yes
Yes
Logic Gates and Circuits
145
IGCSE_CS_TB_Chapter_10.indd 145
13.5.21. 16:32
Chapter 4
Chapter 10
Let’s Map It
Let’s Review

HARDWARE
What logic gate matches these truth tables?
SOFTWARE
Software and hardware are essential to work together.

SYSTEM
A
B
X
A
B
X
























Label the following logic gates:
APPLICATION
Allows a
computer to
function


Allows a
computer to
be used
Draw the logic circuit for the following statement X = (A AND B) AND (NOT C).
Complete a combined truth table including any intermediate outputs for the following: <?>
A
P
AND
B
OR
X
C
Operating System
Enables a user to interact with the computer.
Applications are required to enable a user to
carry out tasks and work.

Draw the correct logic gate circuit and truth tables to match these Boolean algebra expressions:

A˙B
A+B
Ā
Draw the logic circuit diagram and corresponding truth table represented by the below Boolean algebra epressions.
Consider the logic statement:
X =  If [(A is NOT  OR B = ) NAND C is ] NOR [(A is  AND C is ) NAND B is ]
A
Interrupts
All software starts as code
X
B
A stop in a process needing a user or program input.
Python
1
2
3
Handled in order
of priority.
Perl
C++
Java
C#
C
4
Integrated Development Environment
Low- and high-level languages
X
1
2
00110 111001
3
4
Code
Editor
if a == 10:
b += 1
Low
5
High
6
7
8
9
10
Simulation
Translator
Compiler/Interpreter
A
B
C
























Working space
X
11
Software
IGCSE_CS_TB_Chapter_4.indd 65
65
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The following are also included at the end of the book:
162
Logic gates and circuits
IGCSE_CS_TB_Chapter_10.indd 162
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• Answers – provided for questions in Let’s Review (only numerical and short answers are included)
• Glossary – provided to give you a list of the vocabulary words and definitions highlighted in Word Alert
• Index – provided to help you search for key terms and phrases in the book
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Contents
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CHAPTER
1
Computer Systems
QUESTIONS
• What is data?
At the end of this chapter, you will be able to:
• How is data represented by computers?
• How is data stored and compressed for use?
convert between the binary, denary and hexadecimal number systems
understand why hexadecimal is used for representing data
add two -bit binary numbers and know why overflow happens
perform both a left and right logical binary shift
use two’s compliment to represent positive and negative binary numbers
understand how a computer represents text, sound and images
identify the different data storage measurements
understand how to calculate the size of a file
understand why files need to be compressed
explain how files are compressed using lossy and lossless compression methods
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Chapter 1
WORD ALERT
Efficiently: to perform
something in a
well-organised and
competent way.
DEFINITION
Binary: a number system
that contains just 2
numbers, 0 and 1, and
the number system
that a computer uses to
process data.
QUICK CHECK
What is the difference
between a base-10 and a
base-2 number system?
Computers and computing devices are capable of processing millions of pieces of information every
second. Computers read and write an enormous variety of information; in order for the processing
to happen efficiently, that information must be broken down into code that every computer can
understand. Information used by a computer is called data.
The code that computers and machines use to process information is called binary. This is a number
system that only uses two digits,  and . All data that a computer is required to process has to be
converted into binary in order to be understood. This chapter will explore how computer systems
represent data in a variety of ways.
. Number Systems
In order to understand the binary number system,
we must first understand the decimal, or denary,
number system that we are used to. There are several
different theories about how ancient civilisations
began counting in decimal numbers. One theory is
that people began counting using their hands, and
we have two hands, each with four fingers and one
thumb making up ten digits.
.. Denary Number System
Humans probably started to count using
the ten digits that they had on their hands.
The denary system is a base- system, meaning that there are ten digits that form the basis of the
place value system. All numbers in the denary system are formed from , , , , , , , ,  or , and
the place value of each position of the decimal numbers is ten times larger than the place to its right,
written in powers – , ,  and so on.
WORD ALERT
Powers: the product
obtained when a number
is multiplied by itself a
certain number of times.
Worked Example
We can represent the denary number  as in the table below:
Hundreds
of thousands
Tens of
thousands
Thousands
Hundreds
Tens
Units









 ×  = 
 ×  = 
 ×  = 


 ×  =



 ×  =


 ×  =




 +  +  +  +  +  = 
.. Binary Number System
HELPFUL NOTES
When reading binary
numbers, it is important
to read them from right
to left.
2
SB CS PP.indb 2
Binary is a base- system, meaning that only two digits form the basis of the place value system. All
numbers in the binary system are formed from either  or . The place value of each position of the
binary numbers is two times larger than the place to its right, otherwise written in powers, , , 
and so on.
You will notice in the worked example that the columns increase by a power of  from the first
column as you read from right to left.
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Chapter 1
Worked Example
We would represent the binary number  in the table below:















 ×  = 
× =
× =
× =
 ×  = 




DEFINITION
Transistors: a small
electronics device that
amplifies electrical
current.
 +  +  +  +  = 
Therefore, the binary number  represents  in denary.
Computers use the binary system because all of the processing takes place using components
such as registers and memory. These components are made up of transistors that can hold either
an electric charge () or no electric charge (). Logic gates are used to make decisions about the
processing of data, and they have two options – on () or off (). Depending on the gate, data bits are
either kept the same, or switched from  to  or  to  for the operation being carried out.
LINK
See Chapter 10 for
more information about
logic gates.
.. Hexadecimal Number System
REFLECT
The hexadecimal number system is another number system that computers use for processing.
• It is different from the binary and denary systems as it is a base- system.
• It is similar to the denary system as it begins with the digits –, but it also uses the alphabetic
characters A–F to form the remainder of its place values.
Computers only use binary code, however the conversion to hexadecimal is mostly for human
benefit as this conversion shortens the long binary codes. This is illustrated by the conversion table
below. Note that the first ten digits are identical.
Denary
















Hexadecimal










A
B
C
D
E
F
We will discuss the uses of these in section ..
. Binary, Denary and Hexadecimal
Conversions
Have you ever seen what
looks like a hexadecimal
number on your
computer? If you find one
try and convert it to a
denary number.
WB
LINK
Consolidate your
understanding by
completing Exercise 1,
page 1 in the Workbook.
LINK
Section 1.3.
To better understand how a computer carries out the processing of numerical information, it
is important to know how to convert numbers from one system to another. There are various
mathematical approaches to these conversions.
.. Converting a Denary Number to Binary
WORD ALERT
An easy way to convert a denary number into binary is to use the ‘divide by ’ method:
• Divide the number by  each time and note the remainder.
• When you are unable to divide by  any further, the sequence of remainders becomes the binary
number that represents the denary number you began with.
• These remainders should be read from the last division to the first.
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SB CS PP.indb 3
Remainder: the number
left over in a division
in which one quantity
does not exactly divide
another.
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Chapter 1
For example:
29





divided by  =  remainder
divided by  =  remainder
divided by  =  remainder
divided by  =  remainder
divided by  =  remainder





Read in this
direction
Therefore,  in binary notation would be .
.. Converting a Binary Number to Denary
When converting a binary number to denary, it is important to use the rules of place value. Each time
you move a place to the right, the places increase in value by  times the amount of the previous place.
LINK
WB
Consolidate your
understanding by
completing Exercise 2,
page 2 in the Workbook.
Tens thousands
Thousands
Hundreds
Tens
Units
s
s
s
s
s
So, applying place value to a denary number like  will look like this:
Tens thousands
Thousands
Hundreds
Tens
Units
s
s
s
s
s





 ×  = 
 ×  = 
 ×  = 
 ×  = 
×=
 +  +  +  +  = 
LINK
Section 1.1.2.
HELPFUL NOTES
You can continue writing
place values for binary
numbers and keep
doubling the places in
each column. The normal
length of number is 8 bits.
Worked Example
Binary place values can be written in a similar way (see section ..), but the difference here is
that the places double in value from to the previous place.





Therefore, you can apply place value to a binary number like  as follows:










 ×  = 
×=
×=
×=
×=
 +  +  +  +  = 
So, using the mathematics above, the binary number  is  in denary.
ENRICHMENT
Can you write your date
of birth in binary?
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SB CS PP.indb 4
Activity
Show your working out for these exercises.
 Convert the denary number  into binary.
 Convert the denary number  into binary.
 Convert the binary number  into denary.
 Convert the binary number  into denary.
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Chapter 1
.. Converting a Denary Number to Hexadecimal
Using Binary
To convert a denary number to hexadecimal, it is important to know the binary equivalents of the
first  hexadecimal digits (see section ..).
Denary number
Hexadecimal digit
Binary code


























A
B
C
D
E
F
















The table shows that converting any of the first  denary digits into its hexadecimal equivalent is
straightforward. However, converting denary numbers larger than  requires combining the -bit
binary nibbles in the binary code column.
For example, the denary number  in hexadecimal is created by combining the binary nibble
equivalent to denary number  and the binary nibble equivalent to denary number .
Combining two binary nibbles in this way creates an -bit binary number, or a byte.
Denary number
Binary nibbles
Hexadecimal notation

 
 ( + )
Worked Example
To convert the denary number  to hexadecimal you would do the following:
• Convert the denary number  to -bit binary using the ‘divide by ’ method, which becomes
 (see section ..).
• To write the denary number as an -bit binary number rather than a binary number, add
three s to the front of the five-digit number – so  becomes . For this conversion
we can then split the two sets of four binary digits into nibbles, to get  .
• Once you have constructed the -bit binary conversion, use the table above to match the
two nibbles to the hexadecimal column. In this instance, the nibble  is the equivalent of
the hexadecimal digit , and the nibble  is the equivalent of the hexadecimal digit F.
Denary number
Binary equivalent
-bit binary
Hexadecimal notation


 
F
QUICK CHECK
What are the differences
between binary and
hexadecimal?
LINK
Section 1.1.3.
DEFINITION
Nibble: a set of four
binary bits.
HELPFUL NOTES
Bytes are a common
measurement of bits.
Octets, or groups of 8, are
used to represent different
types of data.
LINK
See section 1.2 to
refresh your memory
about denary to binary
conversion.
LINK
Section 1.2.1.
Therefore, combining the two digits gives the hexadecimal code F.
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Chapter 1
.. Converting a Hexadecimal Number to Denary
Using Binary
LINK
Section 1.2.2.
In the same way that you can use binary to convert from denary to hexadecimal, you can also
convert the opposite way:
• Take the hexadecimal number, separate the digits, and then convert those digits back to
binary nibbles.
• Once combined into an -bit binary number, use the place value method (see section ..) to
convert the binary number back to denary.
Worked Example
To convert the hexadecimal number C to denary, do the following:
. Separate the two parts of the hexadecimal number into  and C.
. Using the table in section .., convert the two hexadecimal digits into their binary
nibble equivalents – hexadecimal digit  is equivalent to the binary nibble , and the
hexadecimal digit C is equivalent to the binary nibble .
. The two binary nibbles combined make the -bit binary number .
. Put the -bit binary code into a binary place value table:
LINK
See section 1.2 to remind
yourself about the place
value method.
















 ×  = 
 ×  = 
 ×  = 
 ×  = 
×=
×=
×= ×=
 +  +  +  +  +  +  +  = 
Therefore, the hexadecimal code C is equivalent to the denary number .
Activity




Show your working out for these exercises.
Convert the denary number  into hexadecimal, using binary to help you.
Convert the denary number  into hexadecimal.
Convert the hexadecimal number F into denary, using binary to help you.
Convert the hexadecimal number A into denary.
. Examples of the Use of Hexadecimal
Numbers in Data Representation
Data in its most basic form has to be converted to binary so it can be processed by a computer.
However, hexadecimal numbers are useful for a number of purposes, and are easier for humans to
read than long strings of binary bits.
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Chapter 1
Hexadecimal numbers can be found in computer science in the following examples:
MAC Address
Media Access Control
A number that identifies a network interface
controller of a device on a network.
:::d::a
HEXADECIMAL
NUMBERS
Error codes
Often operating system errors are represented
with hexadecimal numbers for reference.
xCDL
HTML Colour Codes
Websites use colour codes to represent one of
the  million colours in the palette.
IPv6 Address
Internet Protocol version 6
A number that identifies locations of devices for
the routing of data packets across the internet.
:da:ae::
. Binary Addition
WB
Addition is one of the most common mathematical operations a computer performs. To appreciate
this, it is important to understand how to carry out binary addition.
Before attempting binary addition, we must look at the similarities with denary addition because the
two processes are alike.
LINK
Consolidate your
understanding by
completing Exercises 3
and 4, pages 5-10 in the
Workbook.
.. Adding Two Binary Numbers Together
To add together the two denary numbers  and , we would place them one above the other,
draw a line underneath the sum and add the columns, starting from the numbers on the right.
Where the sum of the numbers in the column equals  or more, we carry the tens underneath the
next column according to place value.
  
+  
  


REFLECT
Note the similarities
between binary and
denary addition –
always start with the
right-hand column.
The total of  +  is therefore .
Adding together two binary numbers is a very similar process. However, it is important that the two
binary numbers have the same number of binary digits.
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Chapter 1
Worked Example
Add together the binary numbers  and  as follows:
• Write the numbers out in columns, as if you were adding two denary numbers.  would
become .
• Begin from the furthest right and add the numbers in each column.
  
+  
  
The binary number  is equal to  in denary, and the binary number  is equal to  in denary.
QUICK CHECK
What would you need to
do in the addition to add
two 1s in one column?
 +  =  and the binary number that is produced by the addition () is equal to the denary
number .
As with denary, we carry values when adding two s in the same column.
Worked Example
Add the binary numbers  and  as follows:
• Write the numbers out in columns as if you were adding two denary numbers.
• Begin from the furthest right and add the numbers in each column.
   
+    
   
When you add the two s in the third column, this becomes a , and  is carried across to the
next column. This also then produces an addition of two s, which means that a new column
has to be created.
The binary number  is equivalent to the denary number , and the binary number  is
equivalent to the denary number .
 +  =  and the binary number that is produced by the addition () is equal to the
denary number .
.. Overflows
As we learnt in the previous section, adding together binary numbers can often lead to the creation
of an additional column on the left-hand side of the number.
Activity
Show your working out for these exercises.
 Convert the denary numbers  and  to binary and perform an addition on the two numbers.
 Convert the denary numbers  and  to binary and perform an addition on the two numbers.
HELPFUL NOTES
The number 255 is
significant in 8-bit binary
as it is the largest number
that can be represented
in an 8-bit binary octet.
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SB CS PP.indb 8
To apply this theory to a computer, if a register in a central processing unit (CPU) had a capacity
of  bits, the largest binary number that it could possibly hold would be , equivalent to the
denary number .
If one more bit was added to this number, it would push the number above the capacity of the
register and would cause an overflow error.
Computer Systems
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Chapter 1
This is highlighted by the following sum, which is a binary addition of  + :
+
       


       
       
As the column additions carry forward a  each time, eventually a ninth column is added. This creates
a total that becomes a binary number consisting of  bits, one more than the maximum capacity of
 bits. In this instance, the CPU will drop the extra digit, or the overflow digit, because it has nowhere
to store it. The computer would then think that  +  = .
This action would cause an overflow error, which means that there is not enough capacity to carry
out an instruction, and this may make the computer processing unstable or stop.
Most modern computing devices have a much larger capacity than  bits, however, overflow errors
can still occur if the arithmetic and additions push the numbers being returned above that capacity.
WORD ALERT
Overflow: the generation
of a number or other data
item that is too large for
the assigned location or
memory space.
Shift: movement either
to the left or right.
.. Binary Shifting
So far we have only looked at addition. Computers are capable of carrying out logical arithmetic on
the binary numbers that they process, and for multiplication and division a CPU uses a process called
binary shift. To understand this, we must refresh our memory about binary place value. When we
converted a binary number to denary, we used the base- table below:








We will now explore multiplication and division, using the binary place value table to understand the
process of shifting, or logical shifts.
... Multiplication
For a CPU to multiply a binary number, the number needs to be shifted to the left and will fill the
remaining gaps with zeros. For example:
• multiplying by  shifts the digits one place to the left
• multiplying by  shifts the digits two places to the left
• multiplying by  shifts the digits three places to the left
You will notice that multiplications happen in line with the order of place value in the base-
sequence.
WB
LINK
Consolidate your
understanding by
completing Exercise 5,
page 10 in the Workbook.
REFLECT
How many shifts to the
left would take place if
you were multiplying a
binary number by 32?
Worked Example
Take the binary number , equivalent to  in denary and a multiplication of  × .
We would begin with the number written like this:












Multiplication by  requires the digits to be shifted to the left by one place, and the gap is filled
with a zero:













Therefore, the left binary shift operation gives a binary number of , equivalent to the
number  in denary.
Computer Systems
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Chapter 1
... Division
For a CPU to divide a binary number, the number needs to be shifted to the right:
• dividing by  shifts the digits one place to the right
• dividing by  shifts the digits two places to the right
• dividing by  shifts the digits three places to the right
You will notice that divisions happen in line with the order of place value in the base- sequence.
Worked Example
Take the binary number , equivalent to  in denary and a division of  ÷ .
We would begin with the number written like this:














A division by  requires the digits to shifted to the right by one place:













Therefore, the left binary shift operation gives a binary number of , equivalent to the
number  in denary.
... Binary Shifts with -bit Binary Numbers
REFLECT
How many shifts to the
right would take place
if you were dividing a
binary number by 8?
LINK
See Chapter 3 to learn
about the role of registers
in the CPU.
HELPFUL NOTES
The most significant
and the least significant
bits are at the far left or
right of a binary number,
respectively.
LINK
Section 1.4.2.
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SB CS PP.indb 10
We have learnt about binary shifts left and right when multiplying and dividing with small binary
numbers. It is important to also learn what happens when multiplying or dividing -bit binary numbers.
This is because registers contained within the CPU (see Chapter ) often have -bit limits on the
amount of data they can hold at any one time. If an -bit binary number needs to be multiplied the
shifting process can cause bits to be lost at one end of the register, and zeros added at the opposite
end. This process is known as losing the ‘most significant’ bit and can cause data to lose precision. It
also provides the mathematical explanation for an overflow error.
Worked Example
Multiplying an -bit binary number by 
If we wish to multiply the binary number  (the equivalent to denary number ), we
would first write the number in the place value table:
















We would then perform a shift of one place to the left:
















1
However, what has happened to the  that was placed in the furthest-left column?
The multiplication shift produces the binary number  – the equivalent to denary
number  and not , which arithmetic suggests would be returned. This number is larger
than the  () capacity that the -bit register can store (see section ..).
This bit is called the ‘most significant bit’, and when it is shifted beyond the furthest-left column
the binary data that is stored loses precision due to overflow.
Computer Systems
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Chapter 1
The same process can occur when dividing an -bit binary number. There is also a further level
of complexity, because performing a logical right shift can cause a binary number to become
a decimal.
Worked Example
Dividing an -bit binary number by .
If we wish to divide the binary number  (the equivalent to denary number 189), we
would first write the number in the place value table:
















We would then perform a shift of five places to the left:

















However, what has happened to the binary numbers that have dropped off from the right-hand
column?
The division shift produces the binary number  – the equivalent to denary number  not the
decimal number . that arithmetic suggests would be returned. This is because working with
binary in this way does not use decimals, only positive binary integers. The decimal part of the
number is therefore discarded.
These bits are called the ‘least significant bits’ and when they are shifted beyond the righthand column, just like with multiplication, the binary data that is stored loses precision due
to overflow.
REFLECT
Why do you think that
decimal numbers are
discarded when dividing?
Activity
Show your working out for these problems.
 Multiply the binary number  by .
 Multiply the binary number  by .
 Divide the binary number  by .
 Divide the -bit binary number  by .
.. Two’s Complement
WB
We have looked at positive numbers and the way that they are represented by a CPU. However,
a processor can also represent negative numbers, and there are a few ways it handles this
process.
One of the methods a processor can use to represent negative numbers is called two’s
complement. We can use a reference table to help understand this method.
Computer Systems
SB CS PP.indb 11
LINK
Consolidate your
understanding by
completing Exercise 6,
page 11 in the Workbook.
11
14.5.21. 14:13
Chapter 1
Binary numbers and place values
WORD ALERT
Inverted: reversed or
transformed into its
corresponding opposite.
Denary equivalent
















–








–








–








–








–








–








–








–








































































To represent negative numbers, it is important to think about the place value of the furthest-left bit
in a different way. Processors can be set up to see the bit in the eighth column as a sign bit (shaded).
• If the digit in the sign bit column is a , this indicates that the binary number being represented
is positive.
• If the digit in the sign bit column is a , this indicates that the number being represented is negative.
You will also notice that for each of the -bit positive binary numbers represented in the table, their
negative opposite numbers have had their bits inverted. The final step in this process once all of the
bits have been inverted is to add  to the calculation when completed.
Worked Example
Converting a positive binary integer to a two’s complement -bit integer
To convert the binary number  ( in denary) to a positive two’s complement integer, put
the number into the place value columns, ensuring that the left-hand digit is a  (to show that
positive  is represented).
HELPFUL NOTES
The furthest-left column
represents the sign bit;
this tells us whether a
number is positive or
negative. If the column
contains a 0 the number
is positive, if it contains a
1 the number is negative.
12
SB CS PP.indb 12
















The digit in the shaded left-hand column is the sign bit, and  represents a positive integer. As we
learnt earlier, adding the place columns as shown gives us the denary equivalent:  +  +  = 
Converting a positive two’s complement -bit integer to a binary integer
To convert positive  from a two’s complement integer to a binary integer, we essentially need
to reverse the process above. We would represent the number  as follows:
















The  in the left-hand column indicates a positive number, and the positive two’s complement
-bit binary number can therefore be written as .
Computer Systems
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Chapter 1
Converting a negative binary integer to a two’s complement -bit integer
To represent the binary number  ( in denary) as - and a negative two’s complement
integer, put the number into the place value columns, but invert the s to s and s to s. This
gives you the integer’s complement.
















This time, the sign bit column becomes - as there is a  in that column.
The calculation then becomes – +  +  +  +  = – and  is added to the product to
make –. – =  +  = .
Converting a negative two’s complement -bit integer to a binary integer
In order to achieve this, we would essentially reverse the above process. To convert - we
would first of all write out the table for + and invert the bits. This would then give us the
negative two’s complement -bit binary number .
















ENRICHMENT
Why do you think
that we omit the
inverse of the binary
number representing 0
(00000000)? What would
the denary equivalent
of 11111111 be within
the context of two’s
complement?
. Text, Sound and Images
Modern computers are required to represent data in many different forms. The most basic form
is textual data. However, as we live in an increasingly digital world, the information and data that
humans require to be processed becomes ever more complex.
.. Text Representation
Every character that is input into a computer must be represented by binary code, including
the spaces we type between words and the special characters we use for punctuation. As
textual communication is vital for users around the world, it is important that computers have a
common set of characters that are recognised by a variety of systems. These are called character
sets, and the most common are American Standard Code for Information Interchange (ASCII)
and Unicode.
ASCII code uses seven binary bits to represent all the commonly used characters. This provides a
character set that has  different characters, made up as follows:
•  upper case letters
•  lower case letters
• Digits
• Punctuation marks
The basic form of ASCII does have restrictions, as it does not allow for the representation of
characters such as á or ê, which are commonly used characters in different languages. So Extended
ASCII was created, which allows  characters to be represented, meaning that characters from
languages such as French and Spanish could be stored.
As textual communication developed further and became increasingly global, even Extended ASCII
was too restrictive for all of the different languages and characters required.
Computer Systems
SB CS PP.indb 13
REFLECT
What do you think control
codes are used for?
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Chapter 1
Inserting a special character in Word is made possible by using the Unicode character set.
HELPFUL NOTES
An emoji is made up
of combinations of
different symbols, usually
beginning with a colon.
WORD ALERT
Analogue: using
signals or information
represented by a
continuously variable
physical quantity.
Computers began to be programmed using Unicode to represent text. Unicode uses -bits to
represent the characters in its set, which enables over , characters. In this way, languages such
as Chinese and Arabic, which have many additional characters, can be stored, displayed and shared.
Unicode can also display the pictorial symbols known as ‘emojis’, which are used in the world of
instant messaging and texting.
.. Sound Representation
Just as text can be represented by binary, so too can sound. For a computer to successfully process
sound, the analogue signal input has to be converted into a digital signal. Sound is normally
captured by a microphone, and a piece of software will capture it and convert the analogue to
digital. This recording is called a sample.
The sample is recorded over a period of time measured in seconds. The sample generates a
continuous sound wave that is a measure of amplitude over time.
9
DEFINITION
8
7
Amplitude
Amplitude: the strength of
a sound wave, measured
at the highest level.
6
5
4
3
2
1
0
1
2
3
4
5
6
Time
14
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Chapter 1
The conversion software records the amplitude at each moment in time during the sample. Each
amplitude number (denary) is then converted into binary and stored.
The example in the graph above shows one sample being converted into a sound wave. However,
the recording software is capable of taking multiple samples every second. This number is called the
sample rate and it is measured in hertz, or cycles per second. The greater the sample rate, the larger
the audio file that is created by the software.
Sample rate is also very important in determining the sound quality of the audio – if the rate is too
low, the sound quality will be impaired. Most audio clips are recorded at . kilohertz, which is
suitable for listening while keeping the file at a manageable size for storage.
Bit depth and bit rate is another aspect of digital audio. Bit depth is also known as sample resolution,
and measures how many bits are used to record each sample. A recording with a resolution of 
bits will be lower quality than a recording with a resolution of  bits. The file will also be much larger
at the higher resolution. The bit rate marks how much data is processed for each second of sound
recorded and is formulated by multiplying the sample rate by the sample resolution.
When both the sample rate and sample resolution are increased, so is the accuracy of the audio
recording.
The pixels are stored as a series of binary codes,
and the number of pixels determines the
resolution of an image. The greater the number
of pixels, the higher the resolution and quality of
the image.
Another factor of image representation is colour
depth, which is the number of bits that are
used to represent each colour. If two bits were
used per colour instead of just one, this would
allow twice the number of colours to be used
in a picture. If -bit binary codes were used
to represent colours, there would be ,
possible colours. As the colour depth and
resolution increase, so do both the image size
and the image quality.
Hertz: frequency of
samples, measured in
cycles per second.
WORD ALERT
Impaired: weakened or
damaged.
ENRICHMENT
What is the lowest sample
resolution a sound file
could be recorded at
before the listener would
detect a drop in quality?
.. Image Representation
By their very nature, images are visual; however,
these are also represented by binary numbers.
In the simplest form, we can think of images as
being a grid of pixels where a  is represented
in white and a  is represented in black.
DEFINITION
































































DEFINITION
Pixel: a tiny area of
illumination on a display
screen.
REFLECT
How many colours would
be represented by 4-bit
colour depth?
. Data Storage
Data in computers and computing devices require appropriate storage media. Each device uses
different types of storage media, with advantages and disadvantages.
One thing that is unique to all storage media is the measurement of its capacity. The capacity of the
storage medium is measured in bits.
• A bit can either be a  or a  in binary, and represents one binary decision.
• There are  bits in a nibble, and  bits or  nibbles in a byte.
• Typically, a byte would be the equivalent of one single character typed in a document.
Computer Systems
SB CS PP.indb 15
15
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Chapter 1
There are  bytes in a kibibyte. The reason that there are  bytes rather than  (decimal) is
because of the way that numbers are counted in binary. Binary numbers are counted using a system
of powers, and the next number in the sequence is always double the previous one.











Therefore, kilo is  to the power , equal to  times the value of . Kibi is  to the power of ,
equal to  times the value of .
This table sets out the units of measurement for storage devices in computing.
Unit of measurement
HELPFUL NOTES
You may have heard
the terms kilobytes and
megabytes, rather than
kibibytes and mebibytes.
Kilo and mega refer to
multiples of 1000, rather
than 1024, and so it is
more helpful to use the
terms in the table.
 bit
Equal to
The smallest unit of data storage
 nibble
 bits
 byte
 bits
 kibibyte (KiB)
 bytes
 mebibyte (MiB)
 kibibytes
 gibibyte (GiB)
 mebibytes
 tebibyte (TiB)
 gibibytes
 pebibyte (PiB)
 tebibytes
 exbibyte (EiB)
 pebibytes
 zebibyte (ZiB)
 exbibytes
 yobibyte (YiB)
 zebibytes
As of yet, there is no measurement of computer storage larger than yobibytes, mainly because
humans have not yet needed this. Each storage device is capable of supporting storage media up to
a certain number of bytes depending upon its type and usage.
.. Calculating the File Size of an Image File
It is important to know how the size of an image file is calculated for storage on a computer’s hard
disk. There are four steps:
. Multiply the number of horizontal pixels by the number of vertical pixels to obtain the total
number of pixels.
. Multiply the total number of pixels by the colour depth of the image to obtain the total number
of bits.
. Divide the total number of bits by  to get the file size in bytes.
. Divide the file size in bytes by  to get the file size in kibibytes.
Worked Example
The image here is to be stored on a computer’s hard disk.
To work out the total file size in kibibytes we can use the
following information:
• The number of horizontal pixels is  and the number
of vertical pixels is .
• The colour depth is  bits.
Therefore, the calculation of the file size is as follows:
 vertical pixels ×  horizontal pixels =  (total number of pixels)
 ×  (colour depth in bits) =  (total number of bits)
 ÷  =  bytes (file size in bytes)
 ÷  =  KiB (file size in kibibytes)
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.. Calculating the File Size of a Sound File
The size of a sound file can also be calculated by following several steps.
. Obtain the following data about the sound file:
• the sample rate (sometimes referred to as the frequency)
• the resolution (sometimes referred to as the bit depth)
• the number of audio channels that have been recorded (one channel is a mono recording,
and two channels is a stereo recording)
. Multiply the sample rate by the resolution by the number of channels to calculate the bit rate, in
bits per second.
. Multiply the bits per second by the length of the sound recording in seconds, to calculate the
total number of bits.
. Divide the total number of bits by  to get the file size in bytes.
. Divide the file size in bytes by  to get the file size in kibibytes.
. Divide the file size in kibibytes by  to get the file size in mebibytes.
WB
LINK
Consolidate your
understanding by
completing Exercises
1-3, pages 12-14 in the
Workbook.
Worked Example
The sound file below is to be stored on a computer’s hard disk, and we need to work out the
total file size in mebibytes.
We know the following information:
• the sample rate of this sound file is  samples per second (hertz)
• the resolution of the file is  bits per sample
• the number of channels used to make the recording is 
• the sound file is  seconds in length
Therefore, we can calculate the file size as follows:
 ×  ×  =  (the bit rate, in bits per second)
 ×  =  (total number of bits)
 ÷  =  bytes (file size in bytes)
 ÷  =  kib (file size in kibibytes – rounded)
 ÷  = . mib (file size in mebibytes – rounded)
Activity
 Calculate the file size in kibibytes of an image file that has  horizontal pixels and  vertical
pixels, and a colour depth of  bits.
 Calculate the file size of a sound file in mebibytes that has been recorded at a sample rate of
 samples per second, has a resolution of  bits per sample and has been recorded using
two audio channels. The sound file is  seconds in length.
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. Data Compression
DEFINITION
Bandwidth: the
transmission capacity of a
computer network.
As files and media become higher quality, the files we use increase in size. Computers only have a
finite amount of storage capacity, so some software applications can compress the files to store and
share them efficiently . Compression is a technique that reduces the size of a file. The benefits of this
are that files can be sent successfully across a network, which requires lower bandwidth and takes
less time to deliver, and the compressed files also take up less storage space.
There are two types of data compression: lossless and lossy. Each method reduces the number of
bits in a file.
.. Lossless Compression
LINK
In lossless compression, file sizes are reduced but there is no loss of data. A simple example is
converting a text document to a portable document format (or PFD) file.
WB
Consolidate your
understanding by
completing Exercise 2,
page 15 in the Workbook.
A process called run length encoding (RLE) is another method of lossless compression. This is where
a piece of compression software will look for runs of duplicated data and recode these runs as
smaller amounts of data.
For example, if a run of notes for a sound file looked like this:
A
A
A
B
B
B
B
B
C
C






it might be displayed as data like this:




RLE would look at the duplicates in a run, find the number of duplications and would reprogram
the line:
 (three s)
ENRICHMENT
Can you find examples
of different file types that
are created using lossless
compression?
 (five s)
 (two s)
ABC
This way, none of the data is lost but the file is compressed by the software finding efficient savings
of data where possible.
.. Lossy Compression
As the name suggests, in lossy compression data is permanently removed from the file to reduce
the size.
WORD ALERT
mp3: MPEG (Moving
Picture Experts Group: the
organisation that created
the file type) Layer 3.
jpeg: Joint Photographic
Experts Group: the
organisation that created
the file type.
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Some ways the software can do this
include reducing the resolution or colour
depth of an image, or reducing the
sample rate or resolution of a sound file.
When a sound file is converted to an mp3
file this is an example of lossy sound. An
mp file has had enough bits removed
to reduce the file size, but not enough
to change the sound of the sound file
dramatically. This type of compression is
perfect for storing many mp files on personal media-playing devices.
Similarly, when an image is saved as a jpeg file, bits are removed so that the file looks lower in quality
but not enough so that the meaning is lost. Jpegs are often found on websites, as they tend to be
smaller in actual size and this allows the page to load faster.
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Chapter 1
Let’s Map It
Computers display many
forms of information
This is represented
by binary code
• MAC addresses
• IP addresses
• Color codes
BINARY
DENARY
HEXADECIMAL
Binary
Hexadecimal
Denary
POSITIVE +
NEGATIVE -
We can convert between the
ADDITION
MULTIPLICATION
DIVISION
Text
Sound
Can lead to
BINARY SHIFT
Images
File sizes can
be calculated
ASCII
Unicode
Storage
Bits
Bytes
B
I
N
A
R
Y
Kibi bytes
COMPRESSION
Files can be
reduced in size
Mebi bytes
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Chapter 1
Let’s Review


















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What are the differences between the binary, denary and hexadecimal number systems?
What is the number  in binary?
What is the number  in denary?
In which direction should you read a binary number?
Convert the denary number  to hexadecimal, using binary to help you.
Convert the hexadecimal number D to denary, using binary to help you.
Name three examples of the use of hexadecimal numbers in computing.
Multiply the binary number  by  and show the binary result and its denary equivalent.
Divide the binary number  by  and show the binary result and its denary equivalent.
What is the name of the furthest-left bit in an -bit byte, used when multiplying?
What happens to decimal numbers after a binary division is carried out?
What is the name of the process used to convert a positive binary number into its negative
equivalent?
What is the binary number that represents –?
Find the binary number that represents –
What is ASCII and how many characters are contained in the character set?
Explain the difference between a kilobyte and a kibibyte.
An image is  pixels horizontal and  pixels vertical. It has been created with a colour depth
of  bits. What is the file size of the image in kibibytes?
What is the difference between lossless and lossy compression?
Computer Systems
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CHAPTER
2
Data
Transmission
COMPUTER SCIENCE WATCH
Scan the page to watch a clip on the types
of data transmission.
Before watching discuss what you expect
to see or hear.
QUESTIONS
At the end of this chapter, you will be able to:
understand that data is broken down into packets to be transmitted
identify the structure of a data packet
describe the process of packet switching
define how data is transmitted from one device to another, using
different methods of transmission
• How is data transmitted between different
devices?
• How do computers ensure that the data
that is transmitted gets to its intended
destination correctly and accurately?
• Why is it important to keep data secure
when sending it to another device across
a network?
understand what the USB interface is and how it is used to transmit data
understand that data needs to be checked for errors and the different
methods used to do this
explain why data is encrypted and how this is done
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Chapter 2
QUICK CHECK
How are computers
connected together?
How does the
internet work?
ENRICHMENT
The origins of data
packets can be traced
back to the 1800s when
Samuel Morse sent the
first telegraphic message
and invented what is
known as Morse Code,
a series of dots and
dashes that needed to be
translated into letters
and words.
Data transmission is a vital part of electronic communication. In order for computers and humans to
communicate with one another, it is important to understand how that communication data makes
its way around a network, transfers from one device to another and how systems ensure that errors
are detected and corrected. It is also important to learn how encryption keeps data safe and secure
during the transmission process.
. Types and Methods of Data
Transmission
When data is generated by a computer from information provided by human input, it is often
necessary for that data to be transmitted either to another device connected directly to a computer,
or across a network such as the internet to a device elsewhere in the world.
In order for this transmission to occur, data has to be first broken down into packets ready for
sending. A packet is a small chunk of data and, when these are sent across a network, the chunks
have to be put back together again to formulate the original data that was intended to be received.
.. Packet Structure
A packet of data contains the following pieces of information:
Item
Packet header
DEFINITION
Internet Protocol (IP)
address: a unique string
of numbers separated by
full stops that identifies
each computer using the
protocol to communicate
over a network.
Description
This is added to the data prior to sending the packet and contains both
the Internet Protocol (IP) address of the computer that is receiving
the packet, and also the IP address of the computer sending it (the
originator).
The packet header also adds two identification numbers to the data:
the number of packets that the data has been broken down into, and
the packet number. This is used for ‘rebuilding’ the data at the end of
transmission.
Payload
This is the bundle of data that is contained within the packet.
Trailer
Each packet has a trailer which is sometimes known as a footer. It contains
bits of data that tells the receiving device when it has reached the end of
the packet transmission. This is what is known as a validation check, and
the trailer ensures that the data that left one computer matches the data
that has arrived at the other computer. If the check does not match, the
packet will be requested again from the originator.
Originator: the sending
device.
Once data is ready for transmission, it will be broken down into as many packets as are required
to send it by the originator and will then be sent across the network or the internet.
.. Packet Switching
The packets do not travel along cables in the same order that they were created and will often
take different routes across a network to get to their intended destination. This process is called
‘packet switching’ and it means that data can be transmitted by the most suitable route to get to its
intended destination. The routes that are taken by packets are determined by the router, a device
that directs incoming and outgoing traffic on a network.
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Chapter 2
Data being sent along network cables.
As the packets arrive at the destination device, they may arrive out of order. This is where the bits of
data that make up the packet header and the trailer become important, as the receiving device will
wait until all packets have arrived.
Once the packets have all arrived at the destination and the last packet is received, the device will
reorder them into the correct order so that the computer can read the data that it has obtained.
Finally, the trailer is checked for parity with the originating device and, if the data matches, the
transmission process is complete. As with all computing processes, data transmission and packet
switching occurs extremely quickly, in a matter of seconds.
WORD ALERT
Parity: ensuring that
something is the same.
.. Methods of Data Transmission
There are several different methods of transmitting data depending on the type of hardware and
connections being used. This is usually a key decision when it comes to buying a new computer, as a
user will want to know how fast data can be transmitted between devices.
The amount of data that can be transmitted at a given time is called bandwidth. The higher amount
of bandwidth available, the quicker the transmission speed.
The types of transmission that devices can use to perform data transfer are:
• Serial
• Parallel
• Simplex
• Half-Duplex
• Full-Duplex
HELPFUL NOTES
It is important to read
the small print carefully
when purchasing a new
computer to see what
connection ports it
has – this can make a big
difference to your work
efficiency.
Serial Data Transmission
Computer
Figure . Serial transmission.
Computer
Bits
(Single)
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ENRICHMENT
Can you find out when
serial and parallel ports
were no longer included
in computers? What
replaced them and why?
This type of data transmission occurs when a computer or device is connected to another computer
or device using a single data channel. Data is transmitted one bit at a time, sequentially, down
the channel.
An example of this type of data transmission occurs when a computer is connected directly to a modem.
One of the advantages of using a serial transmission method is that it is very reliable for transferring
data over longer distances, although sometimes it is not the most practical. There are also much
fewer errors in serial transmission, as bits are sent one at a time, and only one single channel is
required to achieve this transmission. Thus, this is a lower cost method of transmitting data.
The disadvantage of a serial transmission is that transmission speeds can be slow as only one
channel is being used to transfer data.
Parallel Data Transmission
Computer
Figure . Parallel transmission.
REFLECT
Most modern printers
now are connected to
computers using network
cables and data is
transmitted much faster
this way.
Bits
(Multiple)
Printer
Parallel data transmission is where multiple bits of data are sent at the same time along different
channels in the same cabling.
An example of this type of data transmission is where a computer is connected directly to a printer.
The advantages of this type of transmission is that faster data transmission takes place because of the
multiple channels being used. The disadvantages are that this type of transmission is more expensive
and synchronisation errors can occur due to the separation of data across different channels.
Simplex Data Transmission
Input
Computer
Unidirectional
Figure . Simplex transmission.
QUICK CHECK
What other devices
can you think of that
use unidirectional data
transmission?
Simplex transmission is a one-directional (or unidirectional) mode of data transmission. The data will
only go one way, and the receiver of the data does not send any data back to the sender.
An example of this type of transmission occurs between a keyboard and a monitor. The keyboard
sends input data to be displayed on a monitor, but the monitor does not send any data back to the
keyboard.
The advantage of simplex transmission is that the process can use the full bandwidth of the
channel. The disadvantage of this transmission type is that it is not possible to engage in two-way
transmission using this method, and most forms of communication rely on this to be successful.
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Chapter 2
Half-Duplex Data Transmission
Transmission
Not simultaneous
Figure . Half-duplex data transmission.
In half-duplex transmission, two-way communication is possible because both devices can send and
receive data packets. With half-duplex transmission, although the direction of the data flow can be
reversed, transmission cannot be sent in both directions simultaneously.
As with simplex transmission, the full
bandwidth of the channel is used, but only in
a single direction at any one time.
Simultaneously: at the
same time.
ENRICHMENT
An example of half-duplex data transmission
is in the use of a walkie-talkie handheld
communication device. When one device
sends data, the other device is unable to do
so until the transmission has completed.
One advantage of this type of transmission
is that it enables two-way transmission
using full bandwidth, which is important
for communication, representing an
improvement on simplex transmission. The
disadvantage of half-duplex is that there
are delays in the transmission process due
to the need to wait to be able to use the
bandwidth.
WORD ALERT
Why would half-duplex
data transmission not be
an appropriate method
of data transmission for a
video phone call?
Walkie talkies.
Full-Duplex Data Transmission
WB
LINK
Consolidate your
understanding by
completing Exercises
1-3, pages 17-21 in the
Workbook.
Bi-Directional
Figure . Full-duplex data transmission.
This method of data transmission is bi-directional, and data can flow simultaneously to and from
sender to receiver simultaneously. Full-duplex transmission is made up of two simplex channels,
one flowing in one direction, and the other flowing in the opposite direction. It is the fastest
method of transmitting data.
An example of full-duplex transmission is a telephone network, where users can talk and listen at
the same time.
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The advantages of using full-duplex
transmission are that it is the fastest
method of data transmission due to each
communication using its own simplex
channel, and there are no delays in
receiving data. The disadvantage of using
full-duplex is that some networks are
not capable of utilising the technology,
especially if older equipment is being used,
and the technology is only as good as its
oldest devices.
.. Universal Serial
Bus (USB)
HELPFUL NOTES
USB technology was first
designed and created in
the 1990s by Ajay Bhatt
from the IBM Corporation
and has now become the
standard technology for
plug and play devices in
modern computing.
LINK
WB
Consolidate your
understanding by
completing Exercise 4,
page 22 in the Workbook.
REFLECT
How many different
devices do you own that
uses a USB connection?
WORD ALERT
Ubiquitous: located
everywhere.
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A telephone call is bi-directional.
The Universal Serial Bus (USB) is a type of communication
port that has been built into computers in order to do away
with other older forms of port. As discussed earlier in the
chapter, serial and parallel transmission of data were the
industry standard for sending and receiving bits of data to
and from devices such as printers, keyboards and mice, and
this meant that computers had to be manufactured with
several of these ports built into them.
The USB logo.
The USB port was designed to be a much more versatile
port and, soon after it was designed, computing manufacturers began designing devices that had
USB connectors as a standard. USB connectors come in a variety of types, with Type-A (rectangular)
and Type-B (square with slanted corners) being the most popular type at first, being joined more
recently by Micro-USB and Type-C connectors. Type-C are now the standard for many types of
mobile devices and laptops, due to their ability to supply power as well as transmit data.
USB cables contain two wires for power
supply purposes and two wires for data
transmission. They are designed to be able
to supply power and transmit data across
a variety of different devices. Due to their
inter-operability, USB is now the connection
of choice for manufacturers, and devices
such as keyboards, mice, hard disk drives,
headphones, mobile phones, tablets and
laptops all use the technology.
Different devices have different numbers and
types of USB ports depending on their usage,
and many mobile phones just have one USB
port that is used for both charging the device
and transferring data to other devices.
The advantages of USB are that they are so
ubiquitous, and there are millions of devices
that have been produced that use the
technology in some form. The technology
is very easy to use as the connectors plug in
simply. The ability to supply power as well as
data means that external power sources are
not needed for devices, keeping costs lower.
USB connectors and their ports.
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The disadvantages of USB are that data transmission speeds are still relatively low compared with other
types of transmission (although it is increasing all of the time as the technology develops). Also, the
length of cable can have an effect on the transmission quality, therefore it should not exceed  metres.
. Methods of Error Detection
Despite all of the technology that is
evolving when it comes to data transmission,
sometimes errors can occur in the transfer
of data from sender to receiver. When data
is changed or altered in transmission, it is
known as corruption, and it is usually due to
interference with the data during the process
of transmission. It is therefore important for
computers to be able to detect these errors.
DEFINITION
Corruption: where
something is altered or
changed without a user
knowing.
Parity check: is a bit added
to a string of binary code
as the simplest form of
error detecting code.
There are several methods that are built into
computer processes for error detection, including
the parity check, checksum, echo check and
automatic repeat requests. There are also methods
for checking errors in data entry.
Data transmission errors can lead to problems and
need to be detected and stopped.
.. Parity Check
WORD ALERT
This type of error checking first requires a protocol to be agreed upon between the sender device
and receiver device. A protocol is a set of rules that both devices will follow. When parity check is
used as the method of error detection, the protocol can either be even or odd parity.
Protocol: a set of rules
that are applied to the
transfer of data.
Whichever type of protocol is used, a parity check involves adding an additional binary bit (a  or a )
to the end of a -bit byte to ensure that the number of  bits is either even or odd.
Computer
Computer
10110011 1
10110011 1
Parity bit
Even
Parity bit
Parity check passed
Computer
Computer
10110011 1
10110011 0
Parity bit
Even
Parity bit
Parity check failed
Figure . No Parity check.
Retry
Once the protocol of parity has been agreed, the sender then adds either an extra  or extra  to the
end of the code. The byte is then sent, with the parity bit attached to the receiver. Once the data
has been received, the receiving device will check that the number of  bits is correct according to
the agreed protocol (odd or even). As long as this is the case, then the data transmission has been
successful. If the parity does not match the agreed protocol, the receiving device will ask for the data
to be re-transmitted.
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It is also important to note that a parity check will not always detect an error, if the number of s in
the received byte adds up to the correct parity. It is also important to recognise that the examples
discussed here are in relation to single bytes; when data is transmitted, it is often many multiples of
bytes that are sent. In this instance, the same process occurs, however the parity is calculated either
using a parity byte attached to a set of bytes, or using a parity block, which is a symbol added to the
end of a block of code.
.. Checksum
ENRICHMENT
The arithmetic that is
carried out in checksum
is usually an algorithm of
some description.
This method again requires an agreed protocol to be determined prior to the data transfer, this time
involving a mathematical calculation or sum.
An algorithm is used to calculate a checksum value from the data that will be transmitted, and then the
block of data is transmitted along with the checksum that has been calculated using this method.
The receiving device will then re-use the algorithm based on the data it has received, and will compare
the two checksum values. If the values match, then the data transmission has been successful. If the
checksum values do not match, the receiving device will ask for the data to be re-transmitted.
.. Echo Check
This is a different type of error check, in that there is no agreed protocol prior to transmission. In an
echo check, the receiving device will immediately send a copy of the data back to the sender and
a comparison is carried out. If there is any difference between the two sets of data during the echo
check, the data will be re-transmitted.
.. Automatic Repeat Requests (ARQ)
HELPFUL NOTES
An ARQ is based upon
repetition, and this
repetition will occur
as often as needed
before the data is sent
successfully.
This form of error checking uses the concept of time to ensure successful transmission of data.
When a sending device sends a block of data, the computer will wait for a positive or negative
acknowledgement from the receiving device.
A positive acknowledgement will be a recognition that the receipt of the data has been
successful, and a negative acknowledgment will indicate that data has not been received.
If a positive acknowledgement is received, the ARQ will stop sending the data, but, if a negative
acknowledgement is received, the ARQ will continue sending the data until a positive receipt
is notified.
The ARQ check also recognises that timeouts may occur, in that no acknowledgement is received at
all. In this case, after a set period of time waiting, the data will be sent again, and this will continue
until an acknowledgement comes back to the sender.
.. Check Digits
DEFINITION
Barcode: a machinereadable code in the
form of numbers and a
pattern of parallel lines of
varying widths, printed
on a physical item. This
pattern identifies it from
other barcodes.
ISBN number: International
Standard Book Number,
a global system for
identifying individual
books. ISBN numbers
have 13 digits.
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SB CS PP.indb 28
The error detection systems described above help to
spot errors during the transmission of data between two
different devices. Sometimes, data discrepancies can
occur due to human input errors.
The check digit is an error check that is designed to spot
these human errors and is a final number that is added to
the end of a numerical code. Check digits can be found
on barcodes and ISBN numbers on the back of books.
It is a digit that is calculated using all of the other digits
in the code and, depending on the product, there will be
a particular mathematical calculation that will be carried
out on the code to generate the check digit.
A barcode found on products in shops.
If the check digit does not match the expected result, then it may be that the barcode has been
mis-read or that a human error has occurred. This would then mean that the item code has to be
rechecked to ensure that it is correctly listed and priced.
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Chapter 2
Worked Example
A barcode is created for a new toy on the market. The barcode number is as follows:
  5
ENRICHMENT
The check digit in this barcode is the number 5, this is highlighted in red above.
This has been generated by carrying out the following mathematical calculation:
Step : Add Digit  to Digit 
Step : Divide by Digit 
Step : Add Digit 
+
+=

The computer in the toy store will know this calculation and so, when the barcode is scanned,
the check digit will be read to make sure it matches the expected result.
(
)
Check digits are often
found at the end of
numerical codes, such as
on a barcode. Can you
find the check digit on the
barcode for this book?
. Encryption
As we rely ever more on communication and transmission of data across networks like the internet,
it is so important to ensure that these transmissions are as secure as possible. Insecure transmission
of data can lead to potentially harmful situations and leave your data vulnerable to hacking or
interception.
A way of keeping data safe and secure during transmission is to use a method of protection called
encryption.
The origins of encryption can be traced back to Julius Caesar, in Roman times, who came up with the
fairly simple idea of changing messages by moving the alphabet forwards or backwards a number of
steps. This is called the Caesar cipher. You would first number the alphabet from  to  starting with
the letter ‘a’ and numbering all the way to ‘z’.
Once you have done this, you can then decide on an encryption protocol such as −, meaning that
you move the alphabet backwards two steps, as per the table below:
Text
Cipher
A B C D E F G H I
C D E F G H I
J K L M N O P Q R S T U V W X Y Z
J K L M N O P Q R S T U V W X Y Z A B
REFLECT
It is possible to make your
own Caesar cipher code
wheel to enable different
forms of encryption
protocol to be used.
QUICK CHECK
What types of information
do you think you might
share when buying an
item online?
Therefore, a message such as “HELLO WORLD” would become “JGNNQ YQTNF”. As long as both parties
know the protocol, messages can be deciphered.
Data can contain private or sensitive information, for example, users’ personal information from their
online bank accounts, or payment card details when purchasing an item from a website. When these
packets of data are transmitted across a network, it is vital that this information remains private and
secure to prevent criminals from accessing potentially sensitive information.
When using websites such as online
banking or making online purchases,
you will notice that, when completing a
transaction, the protocol changes from just
hypertext transfer protocol (http) to secure
hypertext transfer protocol (https). This can
be noticed by looking at the address bar of
the browser being used to access the
web page.
WORD ALERT
Transaction: the process
of buying or selling
something.
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WORD ALERT
Decipher: converting
code into normal
language.
Secure http ensures that a secure connection is made between the two devices engaging in the
transfer of data. The data packets are encrypted before they are transmitted across the network and
are decrypted only when they reach their intended destination. This ensures that criminals such
as hackers would be unable to access the private and confidential information as they would be
unable to decipher the encryption. Any data that was intercepted during this process would be
meaningless to the hacker.
The process of encryption requires the devices at either end of the transfer to use an encryption
key to unscramble the secure data. Websites built with encryption technology will give users the
confidence to carry out these transactions.
There are two types of encryption that use keys to scramble and unscramble data: symmetric and
asymmetric encryption.
.. Symmetric Encryption
HELPFUL NOTES
When dealing with the
encryption of computer
data, unencrypted data
is referred to as ‘plaintext’
and encrypted data is
referred to as ‘ciphertext’.
This is the simplest type of data encryption, and involves the
sender and receiver of data having a secret key that is used to
cipher and decipher the data.
A symmetric secret key is usually a string of numbers, a word
or random letters that is merged with the text of a message
to change the data. As both the sender and receiver know
what the key is, it can be easily removed from the message,
leaving the actual text in its place.
The problem with symmetric encryption is that the key has
to be known and shared by both sender and receiver prior to
transmission, meaning that it could potentially be intercepted
and become insecure.
A better and newer method of encryption would be asymmetric
encryption.
LINK
WB
Consolidate your
understanding by
completing the Exercises
from pages 23-25 in the
Workbook.
.. Asymmetric Encryption
Encryption requires the use
of keys.
This type of encryption is also what is called ‘public key encryption’. This type of encryption uses two
different keys to cipher and decipher a message. It is more secure than symmetric encryption which
only uses one key.
When a message is ciphered ready for transmission by a sender, the receiver will generate a pair of
keys: a public key and a private key. The public key is shared with any device that might wish to send
a message to the receiver.
The sender will then use the receiver’s public key to encrypt the message ready for sending.
However, the public key cannot be used to decipher the message. When the receiving device
obtains the message, it then has to use the private key to decipher the message and since this is
never shared, it is a more secure process compared to asymmetric encryption.
Activity
1
2
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You wish to send the following message to your friend:
MEET ME AT THE SHOP ON SATURDAY MORNING
Come up with a cipher key protocol to encrypt this message, encrypt it and ask your friend to
decrypt it using your protocol. Once you have tried this, send a message of your own, using a
different encryption protocol.
How would you encrypt and decipher numbers and punctuation codes, such as
question marks?
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Data Transmission
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Let’s Review
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
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What is a data packet?
Inside a data packet there are three components, what are they called?
What is the job of the trailer in a data packet?
What does packet switching mean?
What is the difference between serial and parallel data transmission?
Explain the link between simplex and full-duplex transmission.
Why is half-duplex transmission not used in telephone communication?
What do the initials USB mean?
Name three devices that have USB connections.
What are two ways that data could be changed during transmission?
What are the two types of parity checks?
True or false: a echo check is where data is checked only by the receiving device.
What is the purpose of a check digit in a barcode?
Explain a timeout when an automatic repeat request occurs.
True or false: asymmetric encryption uses just one key when ciphering and deciphering data.
Why is encryption important when transmitting data?
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CHAPTER
3
Hardware
COMPUTER SCIENCE WATCH
Scan the page to watch a clip on CPUs
and the main characteristics of the Von
Neumann model.
Before watching discuss what you expect
to see or hear.
QUESTIONS
At the end of this chapter, you will be able to:
• understand that a microprocessor is a type of integrated circuit on a
single chip
• How does the CPU control the internal and
external hardware?
• What does computer architecture look like?
• How do the input, output and storage
devices link together in a computer?
• define the role of the central processing unit (CPU) in a computer
• identify how each component in the CPU operates to create the fetchdecode-execute cycle
• explain what can affect the performance of a CPU
• define what is meant by an instruction set
• understand that an embedded system is used to perform a dedicated
function in a range of different systems
• identify a range of different input and output devices
• explain what a sensor is used for, including the type of data they capture
• identify that there are two types of storage: primary and secondary
storage
• understand how virtual memory is created and used
• define what cloud storage is and what the advantages and
disadvantages are
• identify the components required to connect a computer to a
network, including the role of each component
• understand what is meant by a media access control (MAC) address
and an internet protocol (IP) address and how they are used
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. Computer Architecture
DEFINITION
Architecture: how a
computer system is
designed, including the
rules and methods that
the system should follow.
A computer device is made up of a range of components, both internal and external. All the
components have important roles in the successful operation of the device. Whether it is a desktop
computer, a laptop, a tablet or a smartphone, the basic principles of the architecture are the same.
An important part of this architecture is the rules and methods the components follow. Figure .
maps out these principles.
INPUT
PROCESS
OUTPUTS
STORAGE
Figure . A basic computer architecture diagram.
HELPFUL NOTES
In computing terms,
instructions and
information tend to be
qualitative and data is
quantitative (numerical).
WORD ALERT
Intricate: very
complicated or detailed.
All computing devices are based upon the straightforward premise that items of processing
hardware require some input of information. This information is converted into data that the
processor can carry out calculations with and turns the information into instructions. Some of this
data may need to be stored and recalled, and the computer will then produce an output depending
on the instructions and data that has been processed.
.. The Central Processing Unit (CPU)
At the heart of every computer system sits a processor chip.
This central processing unit (CPU) is crucial to the
operation of a computer system, and it is the job
of this device to process the instructions and
data entered through the input devices.
The CPU then uses the data to perform
various operations and ultimately
produces an output. The CPU is
also known as a microprocessor,
which is an intricate set of
circuits contained on a chip.
These circuits are microscopic
in size so can be built into a
variety of devices.
The central
processing unit.
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Chapter 3
.. von Neumann Architecture
In the s, computer scientist and mathematician John von Neumann further developed the
computer architecture principles shown in Figure .. He established a design still used in the
development and manufacture of computer systems today – to work effectively, computer systems
need a method of storing programs while they are running.
ENRICHMENT
What other developments
was John von Neumann
responsible for?
Central processing unit
Control unit
Input
device
Arithmetic / Logic unit
Registers
AC
PC
CIR
MAR
MDR
Output
device
Memory unit
REFLECT
Figure . von Neumann architecture.
This type of architecture is used as the starting point for most computer devices. Von Neumann
discussed how the CPU requires input and produces output, and that the microprocessor
contains several different components: a control unit, an arithmetic logic unit and a set of smaller
components called registers. The architecture also includes a memory unit with instructions and
data, both read from and written to. This acts as a storage bank for instructions that are used
regularly by the CPU while the computer is powered, and is called random access memory (RAM)
(see section ..). Finally, buses or connections carry the data from one component of the CPU to
another, as shown by the arrows in Figure ..
Can you draw the flow
of data between the
different components of
the CPU?
LINK
See section 3.1.7 The
Memory Unit.
.. The Control Unit (CU)
The control unit is the part of the CPU that controls all of the input and output devices as well as the
arithmetic logic unit (ALU) (see below) and the memory unit. The CU is responsible for making sure
all these components follow the instructions it has processed from the input.
.. The Arithmetic Logic Unit (ALU)
As the name suggests, the arithmetic logic unit enables the processor to carry out mathematical
operations on data, such as adding and subtracting, and logical operations, such as AND, OR and
NOT. This is important in respect of processing data, which is numerical digits in its most basic form.
LINK
See Chapter 10 Logic
Gates and Circuits.
.. Registers
There are five different registers contained within a CPU, all of which are data storage areas.
Before data can be processed it must be stored in one of these.
The Memory Address Register
(MAR)
Program Counter
(PC)
The Memory Data Register
(MAR)
The Accumulator
(ACC)
The Current Instruction Register
(CIR)
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REFLECT
What is the fastest current
speed of processor fitted
to computer hardware?
How can you find a
computer’s specification
and the processing
speed?
• The memory address register (MAR) is responsible for remembering the memory location of
data that the processor needs to access.
• The memory data register (MDR) holds data that is being transferred either to or from the
memory unit.
• The accumulator (ACC) stores mathematical or logical results of processing that has been carried out.
• The program counter (PC) contains the address or location of the next instruction to be carried
out by the CPU.
• The current instruction register (CIR) contains the instruction that is being carried out at the
current time.
The processing of instructions and data by these components is carried out extremely quickly, and
this processing speed depends on the specification of the processor installed inside the computer.
.. Buses
Several buses, otherwise known as connections, carry data around a computer. Of these, there are
three specific buses that the CPU uses to transfer information between the control and arithmetic
logic units and the memory unit:
The address bus
The data bus
The control bus
• The address bus carries the address (or
location) but not the data between the memory
unit and the CPU.
• The data bus carries data between the
processor and memory units and the input and
output devices connected to the computer.
• The control bus carries instructions from the
CPU to control the actions of the computer.
.. The Memory Unit
The memory unit of the CPU stores instructions
and processes that the computer needs regularly
while processing data. This is a much faster way
for the CPU to obtain these instructions than
retrieving them from a storage device like a hard
disk. This unit is a component called random
access memory (RAM), so named because the
CPU can directly access any part of the memory.
RAM is a type of volatile memory, in that it does
not retain its contents when the computer
is powered off. The unit is made up of small
microchips, each with its own address, which is
important for speed of access.
Computer bus cables.
Random access
memory.
Activity
Can you draw a flowchart to represent the order that data flows from the input devices, around
the components of the CPU and to the output devices?
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Chapter 3
. The Fetch-Decode-Execute Cycle
Arthmetic
Logic Unit
Input
Devices
Address
Address

LOAD 

SUBSTRACT 

STORE 









Random Access
Memory (RAM)
WB
Registers
Program Counter
Memory Address Register
Memory Data Register
Current Instruction Register
Accumulator
LINK
Consolidate your
understanding by
completing Exercises
1-2, pages 27-30 in the
Workbook.
Key
Address Bus
Data Bus
Control Bus
Figure . Fetch-decode-execute cycle illustrated.
All modern computers with architecture based upon the work of John von Neumann use a method
of processing data known as the fetch-decode-execute cycle. This cycle happens in a matter of
milliseconds and enables a computer to logically process the data it receives in the correct order for
the user’s requirements.
All the component parts of the central processing unit (CPU) are used to make the cycle work. The
cycle begins with an instruction given by a user via an input device and is sent to the control unit
(CU) via the control bus. The CU then moves the appropriate processing instructions into the RAM.
 The program counter stores the address location of the next instruction to be carried out. This
location number is copied into the memory address register (MAR).
 The program counter is incremented or increased by one and this register now stores the next
instruction to be processed.
 The control unit (CU) makes a request to the RAM for the instruction and obtains the address of
the instruction from the MAR by sending a signal along the address bus.
 The data that is being held in the RAM in the correct address is carried along the data bus to the
memory data register (MDR).
 Once the instruction arrives at the MDR, it is copied into the current instruction register (CIR).
 The instruction is then decoded in the CIR using the arithmetic logic unit (ALU) and then
carried out. The result of this processing is stored in the accumulator (ACC).
WORD ALERT
Control bus: a bus that
carries instructions from
the CPU to control the
actions of the computer.
The cycle then begins again.
Once all the necessary instructions have been decoded and executed within the CPU, the CU then
sends the results of the processing to the output devices using the control bus.
. Cores, Cache Memory and Clock Speed
Other components make up part of the CPU and can make a significant difference to the overall
operating speed of a computer. While the CPU processes instructions and data extremely quickly,
other factors can affect a computer’s performance.
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Chapter 3
.. CPU Cores
REFLECT
In traditional computer architecture, there would
be one CU, one ALU and one set of registers that
comprise the CPU. This would be known as a
processing core. Computers are now available that
are dual-core and quad-core, with eight cores or more
also possible within one system.
What is the highest
number of cores that
a computer has been
manufactured with?
With a dual-core processor a computer has two CUs,
two ALUs and two sets of registers, enabling it to
fetch, decode and execute twice as many instructions,
simultaneously. More cores mean more processing
power and a higher capability compared to a system
with a single processor core. Each core can perform
the fetch-decode-execute cycle independently.
LINK
WB
Consolidate your
understanding by
completing Exercise 3,
page 31 in the Workbook.
.. Cache
A CPU core.
Modern CPU chips have a small amount of RAM built in, called a cache memory. This is different
from a computer’s main memory and is used where a processor has instructions and data it needs
regularly. These are stored in the cache for quicker access, rather than fetching the instructions and
data from the main RAM each time they are required.
The bigger the cache memory, the less time it takes for the processor to fetch the instructions and
data it needs most often.
ENRICHMENT
What is meant by
‘overclocking’ a processor?
.. Clock Speed
Clock speed is an important measure in terms of CPU performance capabilities. This refers to
the number of electrical pulses that the clock inside the CPU can produce every second. This
measurement is made in hertz, and modern clock speeds are usually measured in gigahertz. One
gigahertz equals one billion electrical pulses per second.
The higher gigahertz that a processor is clocked at, the more fetch-decode-execute cycles can be
carried out by the CPU.
. Instruction Sets
A set of common instructions have been developed by processor manufacturers so that CPUs
operate as efficiently as possible. This instruction set is all the commands that can be processed by a
CPU. The instructions are the most basic types of command a computer can respond to and execute,
and these are referred to as operations. These operations ensure that the control unit and arithmetic
logic unit can carry out their respective jobs easily.
Operations are made up of opcodes and operands. Opcodes are used to perform an action on an
operand. We refer to coding such as this as machine code.
.. Opcodes
In straightforward terms, an opcode, short for operation code, gives the CPU a precise job that is
required to happen, and the opcode then needs a piece of data to carry out this job on. Opcodes
can either tell the components an operation to carry out or can instruct one of the units to do
something to a particular piece of data. An example of an opcode would be ‘ADD’, ‘DIV’ or ‘GOTO’.
The opcodes are stored on a computer’s hard disk and would usually be copied into the main RAM
when the computer is powered on. The most regularly used opcodes would then be moved from
the RAM to the cache memory.
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Chapter 3
.. Operands
An operand is the data that is required for the specific job as detailed by the opcode. The operand
may be a piece of data itself, or it may be an address location within the main RAM or a register.
Examples of opcodes and operands
• ADD  (where  may be a number to add to a different piece of data held for processing)
• DIV , (where  and  may refer to address locations)
• GOTO  (where  may refer to an address location)
Activity
Make a list of five additional opcodes that a computer uses and write down a definition of what
each opcode does.
. Embedded Systems
When discussing processors and computer systems, we have traditionally tended to think
about desktop and laptop computers. These are referred to as general purpose computers, capable
of performing a wide range of different activities. However, there are other types of computer
system that carry out rather more specific tasks and jobs. An example of this is known as an
embedded system.
With an embedded system a larger device uses a small built-in computer to carry out its
functions in a more effective way. The computer system usually has a very specific job, and only
carries out that job when required.
Embedded systems in the home
Embedded systems outside the home
Dishwashers
Vending machines
GPS and satellite navigation
Lighting systems
Central heating systems
Closed circuit television (security)
A GPS device is
an example of an
embedded system.
Calculators
One of the key features that sets an embedded system apart from a general-purpose system is that
the user is simply a user rather than having an influence over the programming of the device. On
a laptop, for instance, a user can upgrade the operating system of the computer, but on a satellite
navigation device they have to plug the device into a computer and let it update automatically or
send the device away to the manufacturer for an update.
Embedded systems tend to be low power devices due to their limited nature and capabilities. This
does mean that they can be quite compact (for example a watch), and they can also be operated
using a battery for power (such as a calculator).
Activity
Think of three devices in your house that you would classify as an embedded system? For each
device, describe the information and data that it processes, and how a user might interact with
the device.
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. Input Devices
A variety of input and output devices are used to control and interact successfully with computer
software.
An input device is a piece of hardware that a human uses to give commands to and interact with the
computer, and provide data for the computer to use. This data is then processed by the computer to
produce an output.
Keyboard
DEFINITION
Universal serial bus (USB):
a standard connector
found on many different
types of computer and
used to connect external
devices.
Bluetooth: a form of
wireless connection
for connecting devices
together when they are
near each other.
• A keyboard is one of the most
important input devices used to
give data and instructions to a
computer.
• It has a selection of keys that all
perform different tasks.
• Its main role is for the entering
and typing of letters and numbers.
• A keyboard also has arrow keys
for movement, control keys that
perform standard input tasks and
function keys that perform more
specific tasks.
A standard computer keyboard.
• Larger keyboards have a numeric
keypad (see below), which is useful for financial or accounting purposes.
• Laptop keyboards tend to be more compact with essential keys only. This means the keyboard is
lighter and smaller.
• The keyboard is connected to the computer using either a universal serial bus (USB) port or
wirelessly using a Bluetooth connection.
• Tablets and smart phones have electronic touch keypads instead of a physical keyboard.
Numeric Keypad
REFLECT
The QWERTY keyboard
is the standard one used
in computers around the
world. It is named after
the order of the first six
letters. Can you find out
about different types of
keyboard layout?
A numeric keypad is a small
numbered pad of keys or buttons
labelled from  to . It is often
found on a standard computer
keyboard but not usually on
smaller laptops.
Numeric keyboards are also often
located beside locked doors or
control boxes for alarm systems
and are used to gain access to a
building or a room.
While they are useful for entering
numerical data quickly, this keypad
often has a single purpose, such as
entering a keycode. The buttons
or keys also tend to be much
smaller than keys on a computer
keyboard.
A numeric keypad.
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Pointing Devices – Mouse
A mouse is a standard pointing
device, usually packaged with a
computer alongside a keyboard but
also available to buy separately. A
mouse typically has two buttons –
for left and right clicks – and often
has a jog wheel in between the
buttons for easy scrolling.
This device is connected to a
computer using either a USB port
or wirelessly with a Bluetooth
connection.
A standard computer mouse.
A mouse is used with operating
systems and other software for
giving point and click instructions to the computer and for more complicated processes such as
selection and dragging. It works by shining optical light onto a flat surface, which is translated into
directional movements of the onscreen pointer.
Other Pointing Devices
DEFINITION
Operating system: a
piece of software that
communicates with the
hardware and allows
other programs to run.
There are several other pointing devices that operate in a similar way to a mouse.
• Touchpads are pointing devices installed within a laptop for convenience and portability.
• Trackballs are used to point and move in any direction and allow greater accuracy in precision
movements.
• Stylus pens are used with tablets to input graphical information and for digital drawing.
• Gaming controllers are bespoke pointing devices for interacting with gaming scenarios on a
games console.
WORD ALERT
Stylus: a pen that can
be used either directly
onto a screen or a pad
connected to a computer.
ENRICHMENT
Can you find other types
of device that act as a
point and click input?
Think about computerbased devices in your
home – how do you
control them?
A selection of pointing input devices.
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Chapter 3
Real world examples where these pointing devices are found include:
• a trackball on medical equipment
• a stylus pen used for graphic design
• a gaming controller used with a console
Touchpads, trackballs and
gaming control devices.
Touch Screens
A touch screen is made of glass and reacts to a finger
press. They usually have a built-in menu. Once the user
has made a selection with a finger press, the screen
reacts by displaying a different screen or drop-down
menu. The touch screen works with simple decisions
and does not require huge amounts of input data.
They are most common in smartphones and tablets,
but larger touch screens can also be found in public
places such as airports and shopping centres.
There are three different types of touch screen
technology: resistive, capacitive and infra-red.
Resistive Screens
These are the most common type of touch screen. The
name resistive relates to resistance – the amount of
downward pressure made on the screen by the user.
The pressure causes a change in the resistance, or an
increase in voltage. The layers of the screen detects
the voltage change and calculates the co-ordinates of
where the pressure change has happened. This then
enables the processor to react to the pressure and
display the item the user requires.
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A customer uses a touch
screen to give feedback.
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Capacitive Screens
In a capacitive touch screen, there are four electrodes at each corner that maintain an even amount
of voltage across the whole touch screen. Capacitive technology works on the basis of the human
body being naturally conductive, and the electrodes cause a small current flow between the human
finger and the screen. As with a resistive screen, this current flow causes a voltage change, which is
used by the processor to calculate the co-ordinates where this change occurred.
Capacitive screens are more expensive to manufacture than resistive screens, display better quality
images and also the ability for multiple touch sensing.
WORD ALERT
Conductive: heat and
electricity can pass
through an object.
Electrodes: a conductor
where electricity enters or
leaves an object.
Infra-Red Screens
While capacitive and resistive screens work through pressure and conductivity, infra-red screens
emit a constant grid of lights underneath the top surface layer. The technology works when this light
grid is interrupted, and a touch on the infra-red screen causes a disturbance. The disturbance is then
located by the processor and translated into co-ordinates.
An infra-red screen is much more sensitive than capacitive or resistive screens, and only requires a
very light touch to create the interruption. This means that the screens can be much more durable,
however they are susceptible to false touches because of the increased sensitivity.
Scanners
Scanners are used to convert text or images on paper
into digital information as follows:
• A paper document is placed on the scanner and a
beam of light is shone onto the paper.
• This light reflects onto a sensor, which determines
the colour of the text or image on the paper.
• The information is used by the computer, as an input,
to create a digital copy of the document.
Scanners can also be used alongside software called
optical character recognition to convert written
text into digital text, however some words may not be
converted accurately because of the handwriting.
You might also use a scanner to preserve and save old
photographs.
ENRICHMENT
A paper document being scanned
using a flatbed scanner.
The most popular type of scanner is a flatbed scanner,
however handheld scanners and specialist film scanners
perform similar functions.
Scanners can also work in three dimensions and use
reflected laser light to build up a D model of a
scanned object. These images can then be used with a
D printer to create a model.
Camera
WORD ALERT
A web camera (webcam) takes a digital image of the
view in front of its lens. If the camera takes set images
one after the other at a high enough frame rate, this
can be viewed on a computer screen as a video feed.
These videos can then be sent from one computer to
another in the form of a video conference.
Web cameras are either stand-alone devices connected
by a USB port, or they can be built into a laptop or PC
monitor just above the screen.
A web camera (or webcam) used for sending
digital images to other users.
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Scanned documents
have replaced many
forms of paper-based
communication. How
is this technology
being used in business
to replace things that
have traditionally
involved paper?
Video conference:
a form of visual
communication where
users in different places
can see, hear and speak to
each other using a variety
of equipment, including
web cameras, monitors
and microphones.
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These cameras can also be used for security purposes by recording images when movement
is detected in front of the lens. Another popular use of webcams is viewing attractions such as
landmarks or tourist destinations over the internet.
WORD ALERT
Analogue signals:
continuous signals that
cannot be processed
by a computer until
they are converted into
digital data.
Dictation: the process
of reading words into
a microphone so that
they can be converted
from analogue signals to
digital words on a screen.
Microphone
A microphone is used to convert sound
analogue signals into digital information. In
computers microphones are mainly used with
webcams for video-conferencing. The digital
signals are sent to another computer user and
can be heard as a sound. They are also useful
for gaming so players can speak to each other
during multiplayer games. Microphones can
also be used with dictation software to convert
spoken words into digital text.
Many computers have microphones built in,
but external microphones and those built into
specialised headsets are attached to computers
using the audio port.
Barcode Reader
A computer microphone for converting
vocal signals into digital information.
REFLECT
Does the language or
dialect you speak make a
difference to computers
when you are speaking
into a microphone? How
does a computer ‘get
used’ to your voice?
A handheld barcode scanner reads
a barcode with infrared light.
A barcode reader is often found attached to a point of sale (POS) computer in a shop or business.
The reader accesses information about a product within the store. The barcode holds information
such as the product identification number, country of origin and manufacturer. However, it does
not store the price of products, which is held in a database. During the purchase process the
computer scans the barcode information and matches the data to the database to check the
most up-to-date price.
The barcode scanner uses infra-red light to read the bars in the code. This light is reflected back to
the device and is converted into digital data. Barcodes are also used for tracking parcel deliveries or
baggage in airports.
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Quick Response Scanner
A quick response (QR) scanner is a device
that reads QR codes. QR codes tend to look
like square patterns. The codes in the pattern
contain a small amount of data as information
such as website URLs and contact details. Many
smartphones have QR readers and the codes
can be scanned quickly to access information.
The codes avoid the user having to remember
long telephone numbers and website
addresses, because the QR reader will quickly
convert the QR code into the information.
REFLECT
Why would you use
QR codes instead of
barcodes?
A smartphone is used with a
built in QR scanner.
. Output Devices
Output devices are the hardware a computer uses to display or send out the data that has been
processed. Input devices that provide the computer with the instructions are linked to the output
devices, so the user can see or hear the results of those instructions. The choice of output device
depends on the most appropriate use of the data that has been processed.
WORD ALERT
Array: a data structure
that holds related data.
Monitor
A monitor or a screen is a common output device that comes in various sizes and shapes and has
different uses depending on the data being processed and output.
• Monitors are measured diagonally from one corner to another in inches, e.g. a -inch screen.
• The picture that a monitor can display is made up of thousands of coloured dots. These are called
pixels.
• Liquid crystal display (LCD) monitors use a combination of red, green and blue to make any colour
of pixel required for the output.
• Light emitting diode (LED) screens use an array of light emitting pixels.
• Monitors can display a certain number of pixels depending on the quality – more pixels mean a
better quality of picture output.
• However, the larger the monitor the more
expensive they tend to be.
• Most laptop computers come with small
monitors built into the case, whereas
PC towers tend to have stand-alone
external monitors.
• Modern monitors connect to a
computer using a high-definition
multimedia interface (HDMI)
connector.
DEFINITION
HDMI: high-definition
multimedia interface
technology displays
high-definition images
and sound through a
single cable. HDMI is a
standard connection port
for audio/visual devices in
computers.
A large screen monitor in
use in an office.
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Touch screens
A touch screen can be used both as an input
device (refer to page ) and an output device.
Touch screens are used on smartphones and
tablets. They are menu- and choice-driven and
require a user to interact with the screen for it
to work correctly. Once the user has made a
selection with a finger press, the screen reacts
by displaying a different screen.
Digital Light Processing (DLP)
Projector
• A digital light processing (DLP) projector is
a device that connects to a computer and a
monitor to project the video output from the
A touch screen being used to
computer onto a wall or a whiteboard. The
select icon options.
video can be viewed at a much larger size
when projected.
• They are often used in school classrooms or home cinemas for showing video or presentations.
• Projectors are often fixed to the wall or ceiling but can also be portable.
• They are connected to a computer with a high-definition multimedia interface (HDMI) connector.
• DLPs can be large and use powerful bulbs to project the image.
A projector being
used to display a
computer image
at a conference.
Liquid Crystal Display (LCD) Projector
A liquid crystal display (LCD) projector works in a similar way to
a DLP projector. However, the key difference is that red, green
and blue lights are shone through three prisms, then brought
together, or converged, through a second prism to produce the
image. LCD projectors tend to display more vivid images than
DLP projectors, however they are often larger and heavier.
An LCD projector.
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Laser Printer
A laser printer produces a printed
output by transferring powdered toner
onto paper using heat.
The printer connects to a computer
using a universal serial bus (USB)
interface, or wirelessly across a network.
This is a very common type of printer
because it prints quickly and produces
good-quality results either in black
and white or colour, depending on the
model of the printer.
A laser printer commonly found in a
business workplace.
The quality of output and the low
noise levels make laser printers popular
choices for workplaces.
Inkjet Printer
An inkjet printer
commonly found in a
home office.
Inkjet printers
are the cheapest
type of printer.
They work by spraying ink
directly onto paper as it is
heated by the printer. The
ink flows from a cartridge
through tiny holes and
when the paper is fed out
from the printer the ink is
still slightly wet.
Inkjet printers can
produce either black
and white or colour
output and are
popular choices for
use at home and for
printing photographs.
The printer connects
to a computer using
a universal serial bus
(USB) interface, or
wirelessly across a
network.
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WORD ALERT
Interface: a device
or program used to
communicate with a
computer.
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D Printer
ENRICHMENT
Three-dimensional or D printers are output
devices that can create objects rather than
printed pieces of paper.
The 3D printer has
changed the way that
organisations carry out
their planning. Can you
find out the different
types of materials that
a 3D printer uses to
produce models?
D printers often use heated liquid such
as plastic or metal. The type of liquid used
depends on the item being produced. This
liquid is given instructions by the computer
to create a surface and then it solidifies.
The printer uses several layers of this liquid
material to create the shape.
D printers are used mainly by designers to
create prototypes of objects and have been
used in car manufacturing for many years.
The printer is used with a computer and
computer aided design (CAD) software.
A D printer prints a blue model.
ENRICHMENT
Large actuators can be
used to control flood
defences on large rivers,
which protects towns
and cities. Can you
find another example
of a large actuator in
current use?
WORD ALERT
Sound card: an internal
device of a computer
that provides a method
of input and output of
audio signals for use with
multimedia applications.
Speakers
Most computers are fitted with a
speaker, which produces sounds to
alert the user to a problem or to a
decision to be made. Speakers are
also used to output music, sound
and video soundtracks for a highquality multimedia experience. The
sound quality the computer produces
depends on the type of speaker
used. The internal speakers supplied
as standard within a computer tend
to produce lower quality sound,
but externally powered speakers
connected to a computer’s sound
card through an audio port produce
better quality output.
A pair of external computer speakers.
Actuator
An actuator is a mechanical motor that carries out an action
when a computer gives it an instruction. For example, a digital
camera has an actuator built into the lens and the motor moves
the lens in and out depending on the level of zoom required. It
is the actuator that controls this movement. Actuators can be
small, as in the case of a camera, or can be large, such as those
that control heavy duty computer-controlled drills.
A digital camera with an actuator
built into the zoom lens.
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. Sensors
Sensors are usually external devices that are
connected to a computer for measuring
something, such as temperature, light or moisture.
The sensor tends to be located in a suitable
position for collecting the information, and then
sends measurements at regular intervals to the
computer for analysis. These measurements are
converted into readable data. For example, sensors
are used to detect certain changes in a home and
automatically turn the central heating on when
the temperature drops below a set level.
DEFINITION
Small microprocessors can be used in situations
where a portable computer is needed, for example
in a restaurant kitchen.
A moisture sensor.
Types of Sensors
Sensor
Microprocessor:
Microprocessors are
integrated circuits that
contain all the functions
of a CPU of a computer.
Data captured
Data type
Example of use
Acoustic
Sound levels
At a concert
Decibels
Accelerometer
Whether an object is
static or in motion; can
detect motion changes
Fitness tracking
devices
Kilometres/miles per
hour
Flow
The amount of liquid
or vapour that passes
through them
Medical equipment
Millilitres, vapour
pressure
Gas
The presence of gas
Used by gas
engineers
Cubic metres/feet
Humidity and
moisture
The amount of moisture
in the air
Air conditioning
systems
Grams per cubic
metre
Infra-red
Light in the infra-red
spectrum – often used for
measuring distances
Professional sporting
events such as the
javelin
Voltage (on or off )
Level
Height of liquid
In rivers that flood
regularly
Millimetres,
centimetres, metres
Light
The level of ambient light
Security systems or
streetlights
Lux
Ambient: the immediate
surroundings.
Magnetic field
The strength of a
magnetic field
Satellite navigation
and GPS systems
Tesla
pH
Acidity or alkalinity of a
liquid
Water treatment or
sewage systems
pH
Pressure: continuous
physical force exerted on
an object.
Pressure
The pressure of gases or
liquids in a system
For measuring
weather
Millibars, Newtons
Proximity
Can detect the presence
of objects without any
physical contact
Security systems
Centimetres
Temperature
Changes in the ambient
temperature of a room or
object
In a kitchen for food
safety purposes
Degrees Celsius or
Fahrenheit
WB
Consolidate your
understanding by
completing Exercise 1,
page 32 in the Workbook.
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LINK
WORD ALERT
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Activity
Read each of the following scenarios. Select from the table above the most appropriate sensor(s)
for each task. State why this is useful for the user.
A A shop owner wishes to improve security in their store and is also keen to find out how
many customers are visiting the shop each day.
B A band is playing a series of differently sized venues over a three-week period and wants to
set the correct sound levels for their sound system.
C A science laboratory is growing vegetables in a small greenhouse and needs to see how
well the plants are doing over the period of  months.
. Data Storage
DEFINITION
Volatile: loses its
contents when there is
no electrical charge.
It is important to know the differences between memory and storage before we begin to
understand their purpose within a computer system.
• Memory is the microchips, transistors and capacitors that store all the instructions a computer
needs to operate. It can be volatile – one type of memory (RAM) loses its content when a
computer is powered off, but the other type of memory (ROM) has a fixed set of instructions and
these cannot be changed or overwritten.
• Storage refers to the devices within a computer where user information and data such as files,
documents, applications, video and music is kept. This storage is non-volatile, and the contents
remain stored even when the computer is powered off.
Memory is referred to as primary storage because it is essential for the computer to function, to
power up correctly, and ensures that the input, storage and output devices are able to start. There
are two types of primary storage: random access memory (RAM) and read only memory (ROM).
Secondary storage refers to hard disk drives and other types of flash storage devices that are used
for storing user data.
LINK
See section 3.1.2.
.. Primary Storage
Random Access Memory (RAM)
As explored earlier in the chapter, the memory component of the CPU is important to store
instructions and a list of processes that a computer needs regularly while processing data. It is also
a much faster way for a CPU to obtain these instructions than retrieving them from a secondary
storage device like a hard disk. This component is called random access memory (RAM) because
the CPU can directly access any part of the memory. RAM is a type of volatile memory as it does not
retain its contents when the computer is powered off.
Read Only Memory (ROM)
Read only memory (ROM) contains the vital instructions a computer uses when it is first powered
up. The ROM will initialise all the component parts and will enable the input and output devices to
communicate with the hardware inside the computer. The ROM also contains instructions on which
secondary storage device to access first to enable the operating system to load. Once the ROM
instructions have all been carried out, the RAM is then used as the primary storage. The CPU can
access the ROM directly.
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.. Secondary Storage
Secondary storage is any device that is used by a computer to store data longer term. This can
include internal or external hard disk drives, solid state drives, flash storage such as pen drives and
optical storage. Unlike primary storage components, secondary storage is not accessed directly by
the CPU. Secondary storage is non-volatile, meaning that it retains data even when a computer is
powered off.
There are three different types of secondary storage: magnetic, optical and solid state. Each has
different characteristics and uses.
Magnetic Hard Disk Drive
A open view of an internal
magnetic hard drive.
WORD ALERT
Magnetic hard drives are the most common hard drives inside computers. The hard drive consists
of a stack of round metal plates, known as platters. These platters are coated in a magnetic material.
Data is stored within this magnetic material and the platters rotate very quickly on a spindle. An
electromagnetic read/write head, which looks a little bit like a needle, can access, add and remove
data from the platters. The head never touches the metal platters because it floats on an air layer
created by the spinning of the plates. If the head did touch the platters, or some dust was able to
access the drive, this would be enough to damage the device.
This type of storage is known as non-volatile storage. Non-volatile means that the device keeps its
data stored when the device has no power. The storage device is connected directly to the
motherboard of the computer, usually using a
serial advanced technology attachment (SATA)
cable. The hard drive also requires power and is
connected with a second cable directly to the
computer’s power supply. The hard drive is
securely mounted within the casing of a desktop
or laptop computer. For this reason, fixed hard
drives do not need much in the way of external
protection, as they are protected by the casing of
the computer itself.
When a magnetic hard disk has been used and
re-used several times, data can be moved around
the disc and split into different sectors, which can
slow the access to the data by the computer. This
is known as fragmentation – hard disk drives often
have to be defragmented in order to improve the
access to them.
Electromagnetic: the
electrical and magnetic
forces or effects produced
by an electric current.
DEFINITION
Serial advanced
technology attachment
(SATA): a type of cable
usually found inside
computers. It connects
a hard drive with the
motherboard.
A portable external magnetic hard drive.
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Platter: a circular
magnetic plate that is
used for storing data in a
hard disk.
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DEFINITION
Lightning connection:
a high-speed connection
that was developed by
Apple for the purpose
of connecting multiple
external devices to
their computers.
LINK
See Chapter 10 Boolean
Logic.
WORD ALERT
Capacitor: a small
electronics device that
stores an electrical
charge.
A portable magnetic hard drive works in the same way as a fixed hard drive. However, the platters
and read/write head are much smaller, and the hard drive is protected by a durable casing. The
drive is usually connected to a computer using a universal serial bus (USB) connection, or a faster
lightning connection.
Solid State Hard Drive
Solid state hard drives are becoming more
common in computers – mainly due to the
technology getting cheaper. Solid state drives
(SSD) are very similar to flash drives (see Pen
Drives and Flash Drives, below) as they
both use technology known as non-volatile
storage. The key difference between an SSD
and a magnetic drive is that an SSD has no
moving parts. This means that the transfer of
data between the drive and the computer
processor is much quicker. As with the magnetic
drive, this device is connected directly to the
motherboard of the computer, usually using
a SATA cable. An SSD also requires power so is
connected directly to the computer’s power
supply with a second cable.
A solid state hard drive.
In this type of non-volatile storage, the computer forces electrons to be stored within a series of
transistors and capacitors. The transistors hold their electrical charge so data can be stored in the
capacitors for a period of time without electrical power. When the device is reconnected to the
power, the transistors are then charged up again. The forcing (or “flashing”) of electrons into the
capacitors and transistors gives this type of device its name – flash storage. This type of storage
does degrade under extreme temperatures and the lifespan is determined by the number of
read/write cycles.
SSD such as flash memory use either NAND or NOR technology. The main difference between these
is the way the memory cells inside the semiconductor chips are wired together.
ENRICHMENT
Computers are now
increasingly sold with
minimal internal storage,
and users have ‘cloud’
storage instead. What
do you understand
about storing files
and documents in the
cloud, and what are
the advantages and
disadvantages of doing so?
LINK
See the reference to nonvolatile storage earlier in
the chapter.
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• NAND (NOT AND) technology is better for writing and erasing data, and is cheaper to
manufacture. NOR (NOT OR) technology is better for reading data. Therefore, NAND technology is
more common in computing devices.
• A NAND flash memory device contains transistors called control gates and floating gates,
and the writing and erasing of data to the device takes place within this component. Control
gates sit on top of floating gates. Electrons that register as a , as opposed to a , are squeezed
through the gates and are stored as the data that the user requires. When this flow occurs, the
electron value changes from  to .
Portable SSDs are also becoming more popular. These are essentially high-capacity flash storage
drives that connect to a computer using a USB connection or a faster lightning connection.
Pen Drives and Flash Drives
A folding USB pen drive.
Pen drives and flash drives are remarkably similar
in terms of their general characteristics, and
both are non-volatile flash storage devices.
A flash drive is a collective term for any
drive that uses flash technology to store data.
Examples include pen drives, card readers or the
storage inside small devices such as digital cameras or television set
top boxes. While flash drives do not have unlimited capacity storage space, they
do tend to have enough to store a large amount of data depending on the purpose.
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A pen drive, sometimes known as a thumb drive, is a type of flash drive that is designed to insert
directly into a USB port on a computer. Pen drives tend to be smaller in capacity than other flash
drives, because their main intended use is portability – they can be moved between computers
for transferring data from one to another. While pen drives are very useful, it is important that they
are not used as the only storage device for personal data; as discussed earlier, the nature of flash
storage means that the technology degrades over multiple read-write cycles, and data could be lost.
Pen drives are often used as personal data backup storage devices.
WORD ALERT
Portability: the ability to
carry or move something.
Degrades: breaks down
or deteriorates.
Optical Drives
Some desktop computers are fitted with an optical disc drive. These drives
can read from and write to a variety of media, including compact discs (CD),
digital versatile discs (DVD) and Blu-ray discs (BD). Optical disc drives are so
called because they use laser light and the light spectrum to read or write
the data. Optical drives are becoming less common in desktop or laptop
computers as manufacturers attempt to make devices slimmer and lighter.
They are, however, a common feature of games consoles.
• Compact disc (CD) drives: The most basic CD drive can only read a
software application CD or an audio CD. However, CD-R/W/RW drives
(CD readable/writable/re-writable) are also capable of writing and/or rewriting data to compatible media. Basic CD drives have been a feature of
An optical disc drive.
music stereo systems for many years, and the CD is still a popular format for
delivering music to consumers.
• Digital versatile disc (DVD) drives: DVD drives are similar to CD drives, in that the basic drives
can only read applications or video formats such as films. DVD-R/W/RW drives (DVD readable/
writable/re-writable) are also capable of writing and re-writing data to discs. Stand-alone DVD
players are common in many home media set ups, and the DVD is a popular format for distributing
films and computer applications software to consumers.
• Blu-ray disc (BD) drives: Many newer laptops and games consoles are fitted with BD drives.
This format is popular for distributing high-definition media content to consumers. The term
Blu-ray refers to the blue laser that reads the data on the disc, which uses a much shorter
wavelength than the standard red laser in CD and DVD disc drives. This shorter wavelength
means much more information can be stored on a BD, even though they are the same physical
size as CDs and DVDs.
Optical storage devices such as CD/DVD/BD-rewriting drives use the in-built laser to create and read
pits and lands as the disc spins. A pit represents a  and a land represents a  to enable data to be
reflected or digitally read from optical media. When data is being written to an optical disc, a read/
write head moves across the surface of the disk and the laser burns a pit into the surface of the disc.
These pits and the spaces between the pits (lands) enables the laser to reflect back and convert the
data to ’s and ’s – binary data, that is ready to be processed.
. Virtual Memory
Virtual memory is created by a computer when it has many processes running at the same time.
Sometimes, the RAM can become overloaded with trying to process too many instructions at once,
so the operating system will use a portion of the secondary storage, usually the internal hard disk,
and will designate it a temporary area of RAM.
This type of memory is much slower because the data is having to travel much further than if it was
contained within the actual RAM.
Another thing that causes the computer to operate more slowly is the process of paging or swapping data
between the virtual memory and the RAM. Paging is where the computer will move instructions that it
does not currently need out of the RAM into the virtual memory and swap in instructions that it does need.
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REFLECT
What advice would you
give to somebody who
told you that they only
use their flash storage
drive to store important
files or documents?
REFLECT
Optical discs have
changed over a short
space of time, and there
was quite a rapid move
from CD to DVD to Blu-ray.
It looks now like the days
of the optical disc will
soon come to an end. Can
you think of anything you
do that would be difficult
if you didn’t have a disc?
ENRICHMENT
Many games consoles
are moving away from
disc-based games and
are moving to something
called DLC (downloadable
content). Why do you
think the disc is now
used less?
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. Cloud Storage
ENRICHMENT
Do you think that the
commonality of solid state
hard disks will improve
virtualisation? Is there an
improvement that could
be made to the technology
of RAM that would remove
the need for virtual
memory?
HELPFUL NOTES
Many mobile phone
services come with cloud
storage plans, which is
enabling manufacturers
to reduce the amount
of flash storage inside
a phone. This frees up
space for users to install
more applications on
their phones, as we
increasingly rely on
mobile technology to
access essential services.
LINK
With cloud storage, files, data, documents, images, music
and video are stored in a remote location. Users
purchase some space on an external server that is
located somewhere in the world, and access it via
the world wide web. The server is connected to
the internet and can be downloaded from and
uploaded to as necessary.
Cloud storage is often used as backup and
is also very good for sharing files with other
people. The other advantage is that data can
be accessed from anywhere with an internet
connection.
The disadvantage of using cloud storage is that
if there is no internet connection then the files
cannot be accessed. Additionally, it is the job of the
organisation providing the storage to ensure the security
of the data, and cloud storage is just as susceptible to hackers
as personal storage is.
Cloud computing refers to data
stored externally.
. Network Hardware
WB
Consolidate your
understanding by
completing the Exercises
1-3 from pages 34-38 in
the Workbook.
Computers worldwide connected to the internet.
A computer requires certain hardware to access a network. This hardware is a network interface card
or controller (NIC), and it provides the computer with wired or wireless connections to a network.
When the controller is manufactured, it is given a unique media access control (MAC) address, but
this should not be confused with an Internet Protocol (IP) address.
54
SB CS PP.indb 54
Hardware
14.5.21. 14:14
Chapter 3
.. Media Access Control (MAC) Address
DEFINITION
When the controller connects the computer to the internet, the MAC address gives the controller a
unique address and identifies the device on the network.
Any device that connects to the internet, either wired or wirelessly, has a unique MAC address. These
are made up of a string of numbers, usually from the hexadecimal number system. As the number
is preset at the point of manufacture, the address never changes, even when you connect the
computer to the internet in a different location.
A typical MAC address looks like this:
The address is made up of six groups
of hexadecimal digits and this
represents  bits. The first half of the
address identifies the manufacturer
of the network interface card, and
the second half is the serial number
of the card.
This half of the MAC address
identifies the manufacturer
of the NIC.
Hexadecimal: a number
system that uses 16
characters instead of the
10 characters used in the
decimal system or the
two used in binary.
D0 : 81 : 7A : A6 : 82 : D2
The composition of a
MAC address.
This half identifies the
serial number of the
device.
.. Internet Protocol (IP) Address
An Internet Protocol (IP) address is a unique address issued to the device whenever it connects to
the internet. These addresses are issued either by the internet service provider (ISP) that provides the
connection or the network the computer is connected to.
It is the IP address that enables computers all around the world to communicate with each other via
the internet. Think of an IP address in a similar way to a postal address – without a postal address on
an envelope, letters would not reach their chosen destination.
IP addresses are usually four groups of digits separated by dots.
The digits are between  and , representing  bits. This type
of IP address is known as IPv and has been in use since the
early days of internet usage. This format of IP address allocation
offers almost . billion unique addresses.
IP address
Postal address
63 . 41 . 136 . 21
45 New Street
London
W1 3BL
England
An IPv address and a
As the internet and its use evolved, there was a need for ISPs
postal address.
and networks to issue increasing numbers of IP addresses, as
more devices became internet enabled. A new standard for
the protocol was introduced, called IPv, which allowed for
an increase in unique IP addresses from . billion unique IPv addresses up to an enormous 
undecillion potential unique IPv addresses.
Whereas an IPv IP address is made up of four groups (or octets) of numerical digits separated by
dots, an IPv address is made up of eight groups of hexadecimal numbers separated by colons.
IPv4
ENRICHMENT
How do you find out the
IP address of the computer
you are using?
IPv6
63 . 4 1 . 1 36 . 21
2002 : O d a9 : 6 3a3 : 0 0 0 0 : 0 0 0 0 : 7 b 3f : 0 2 2 0 : 64 66
4 groups of
numerical digits
8 groups of hexadecimal
numbers
IPv addresses compared to IPv addresses.
There are sometimes double colons within an IPv address – where one of the hexadecimal groups
contains all zeros and therefore to save computing space the additional colon marks the gap where
these groups would have sat.
Hardware
SB CS PP.indb 55
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Chapter 3
2002 : O d a 9 : 6 3a3 : 7 b 3f : 0 2 2 0 : 6 4 6 6
The IPv address from above with complete zero groups of hexadecimal numbers
replaced by an additional colon.
When an IP address is issued to a device accessing the internet, the address can be static or dynamic.
REFLECT
What would be the
benefit of a network
administrator setting IP
addresses to static?
A static IP address is created by a user in the settings of the router (see below). These are rare
because static IP addresses can cause problems on a network if set incorrectly.
A dynamically issued address is more common. These are issued by routers on a network using a
service called dynamic host configuration protocol (DHCP). This enables a router to assign an IP
address to any new device that is connected to a network. When a device is removed or unplugged
from the network, the address is recycled to another device that may replace it. The use of DHCP and
dynamic IP addresses ensures that there is no duplication of addresses on a network and enables all
the devices to share the internet connection.
.. Routers
ENRICHMENT
Most home broadband
systems have combined
modem routers provided
by an internet service
provider (ISP). What
would be the benefits
or drawbacks of using
an alternative modem
and router other than
the one from the
broadband provider?
A router enables a home or business to connect devices to the internet and is normally provided
by an internet service provider (ISP). Routers send data to specific destinations on a network using
the IP addresses it has issued to devices at those destinations. A router creates what is called a
local area network (LAN), and often incorporates another piece of vital equipment to make this
connection – a modem.
Modems are used to convert signals from a telephone
or fibre optic line into data that is readable by
a computer, and similarly converts data from a
computer into signals that can be sent down a
telephone line or fibre optic cable. Many modern
routers have modems built in.
A router connects devices
to the internet.
Activity
You have been asked to create a small network for your home. There are eight rooms in the
house: a lounge, a kitchen, a dining room, three bedrooms, an office and a bathroom. There will
be at least one device in each room that will be connected to the internet, as in the table. Draw a
simple sketch map of how the house would be connected and what devices are required for this
connection.
LINK
Room
WB
Consolidate your
understanding by
completing Exercise 1,
page 38 in the Workbook.
56
SB CS PP.indb 56
Device(s)
Lounge
Smart television, games console, tablet
Dining Room
Smart speaker
Kitchen
Smart speaker
Bedroom 
Smart television, games console
Bedroom 
Smart television, laptop
Bedroom 
Smart speaker
Office
Desktop computer, printer, smart speaker
Bathroom
Smart speaker
Hardware
14.5.21. 14:14
Chapter 3
Let’s Map It
HARDWARE
Input
Process
Output
Catche
CPU
RAM
Storage
CPU
CPU
Fetch - Decode - Execute
CPU
CPU
CU
Memory
Unit
Registers
ALU
Cores
Buses
°C/°F
24.1°
24.2°
24.3°
Sensors
Networks
Home
Server
www
Router
Cloud Storage
Hardware
SB CS PP.indb 57
57
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Chapter 3
Let’s Review
















58
SB CS PP.indb 58
What is meant by computer architecture?
What is the job of the central processing unit?
List the five different registers that sit within a CPU.
Describe the von Neumann architecture.
Fill in the gaps: the main method of processing data within the CPU is the __________ _________ - __________ cycle.
Explain the purpose of a bus.
What is the purpose of cache memory?
If a processor has two cores, what is it known as?
What is a processor’s clock speed measured in?
Give an example of an embedded system.
A touch screen as an input device can be either capacitive, resistive or infra-red. Briefly explain
the differences between each type of screen.
What would be the most appropriate sensors to use when measuring average rainfall in an
outdoor location?
Define what is meant by cloud storage.
What is the difference between a MAC address and an IP address?
How does a device that you wish to connect to the internet obtain a dynamic IP address?
What is the main purpose of a router?
Hardware
14.5.21. 14:14
CHAPTER
4
Software
COMPUTER SCIENCE WATCH
Scan the page to watch a clip on
the differences between system and
application software.
Before watching discuss what you expect
to see or hear.
QUESTIONS
• What is the link between hardware and
software?
• How is software essential to the operation
of a computer?
At the end of this chapter, you will be able to:
understand the difference between system software and application
software
• How do humans use software to interact
with computing devices?
• What is programming and how do pieces
of software begin their existence?
define the role and basic functions of an operating system
identify the hardware, firmware and operating systems that are used
to run applications software
define the role and operation of interrupts
identify the difference between a high-level language and a low-level
language
understand the advantages and disadvantages of each type of
language
define the two types of translator: compilers and interpreters
identify the advantages and disadvantages of each type of translator
understand what an integrated development environment is used for,
including its common functions
59
SB CS PP.indb 59
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Chapter 4
A computer system is made up of both hardware (as we have examined in Chapter ) and software,
and both are essential for the successful operation of the system. This chapter will explore different
types of software and how they exist and work. We will also learn about how the different pieces of
software control and use the hardware of the computer.
. Types of Software
There are two different types of software that a computer system uses: system software and application
software. System software is a variety of programs and processes that a computer needs in order to
function. System software that is embedded into hardware devices are known as firmware. Firmware is
often installed onto components of the hardware when the computer is built and users do not need to
involve themselves with the installation of system software at all.
WORD ALERT
Function: in order to
work correctly.
.. System Software and Application Software
DEFINITION
Firmware: small
applications which
enable a computer to
start all of its devices.
An example of system software is the BIOS program that is installed in the Read Only Memory (ROM)
of a computer. BIOS stands for Basic Input Output System, and it is a set of instructions that are
executed by a computer once it receives the power to start all of the necessary hardware.
Utility: a small piece of
software that controls
specific parts of
the hardware.
LINK
Another example of system software is the operating system (OS) of the computer, such as Microsoft’s
Windows OS or Apple’s macOS. The operating system allows users to work with the hardware and
applications software in a user-friendly way, usually through the operation of a mouse and keyboard.
There are often other pieces of system software built
into the operating system that allow a user to control
the power, attached devices and memory. This type
of system software is called utility software.
Application software is the term used for any
software that a user requires in order to make use
of the computer system for their needs. Examples
of applications software are office applications
such as word processors, spreadsheet applications
and presentation software, games, web browsers
and communications software. They are not
essential to the functioning of a computer, but
they may be essential to a user’s particular needs.
WB
Consolidate your
understanding by
completing Exercise 1,
page 42 in the Workbook.
.. The Operating System
A laptop running the Microsoft
Windows operating system.
Most computer systems that we interact with as users have a form of operating system installed on
them, to allow us to quickly begin work or start accessing the applications that we require in our lives.
The operating system is a special piece of system software that manages many things that allow us
to use the system for our needs.
ENRICHMENT
Can you find out
about other types of
operating system, and
their advantages and
disadvantages? Find out
about Linux, and what
makes it different from
the other operating
systems mentioned here.
60
SB CS PP.indb 60
In addition to the roles explored in Figure ., an operating system is also the platform for a computer to
run the applications software that is required by a user. Computer software developers have to ensure
that the software that they design, code and produce is able to be run on multiple operating systems.
Operating systems exist within various systems that require humans to interface with them. Devices such
as personal computers, laptops, mobile phones and smart TV’s all require user interaction. There are various
ways in which the interaction can occur, including textually through a command line interface, visually
using a graphical user interface with point and click methods and verbally using voice commands and
natural language interfaces. Some of the current examples of this that you might find around the home
that use these interfaces are smart speakers such as Google Home and Amazon Alexa, as well as mobile
based apps such as Bixby and Siri.
Software
14.5.21. 14:14
Chapter 4
The Operating System
Managing drivers
Managing peripherals Managing Peripherals
Enables all attached
Enables all attached hardware to
hardware to funtion
function effectively
effectively
Managing Memory
Managing memory
Allows
the computer system
Allows the computer
to move things in and out of
system to move things in memory when needed
and out of memory when
needed
Managing Drivers
Drivers are small utility software
that give specific instructions
Drivers are small utility software
that give specific operating
devices such as printers
instruction to devices such as
printers
Managing FilesManaging files
Helps us to save, retrieve and
files created
Helps us to save, retrieve and
print files created print
Manages Multitasking
Provides Interface
Enables the computer to do
several things at once
Allows us to interact with the
physical hardware
Managing multitasking
Enables the computer to
do several things at once
to
Handling interrupts
Alert us as users when an
Alert us as users when an action
action needs to be carried out
needs to be carried out
Handling Interrupts
Provides interface
Allows us to interact with the
physical hardware
Figure . The role of the operating system.
Creates more effective
and efficient code
Takes less time
to translate
As we will explore in Chapter , system security is something that all computer users have to be
aware of when using devices. The operating system provides a useful line of defence, and usually has
a variety of small utility programs, such as firewalls and authentication, that help to guard against
threats to files. Operating systems create and manage essential user accounts such as the system
Code can be
Things can be hidden
COMPILER
account, administrator user kept
account,
regular user account
and guest user account.
Theyinare
secret
and not detected
codeable to
handle multiple users being able to access the computer, with separate profiles created for each user
VS.
based on their individual needs. This is especially important when it comes to protecting younger
users from accessing unsuitable content.
INTERPRETER
A further feature of operating systems is to manage the memory available within a system. This can
Slower translation
Code is more versatile, can be
involve the allocation of resources
to the hardware to enable the carryingviewed
outonofdifferent
usersystems
instructions,
as it is line-by-line
easily
and also to ensure that the same memory locations are not utilised by different processes.
LINK
See Chapter 5.3.
REFLECT
Why do you think it is
important to enable
different user profiles on a
shared computer?
.. Application Software Running Sequence
Easier for beginners as errors are
easily idatified and corrected
Applications, or ‘apps’, are the pieces of software that users want or need to use as part of their lives, both in
work and leisure usage. It is a combination of the operating system, bootloader (firmware) and hardware
working together that allows application software to operate, and the sequence is crucial to that operation.
The firmware (such as
the BIOS) is run and
activates the hardware
The operating system is
run on the firmware
The applications are
run on the operating
system
Figure . Application software running sequence.
WORD ALERT
.. Interrupts
Handling interrupts are an important function of the operating system. An interrupt is a signal sent
from a device or a program to the operating system that causes a temporary stop in the current
program. When the program is halted and control is transferred to the operating system, it usually
has a decision to make, either to continue running the program, run a different program or require a
further intervention from a user.
When a device sends an interrupt signal, for instance when a user presses a key on a keyboard, the
interrupt is collected by an interrupt handler, and an interrupt service routine is carried out.
This usually involves the interrupt being assigned a place in a queue, so that the handler can decide
which interrupt is the highest priority. The interrupts are then handled according to their importance.
This process happens so fast that it is impossible for a user to notice that the operating system has
been interrupted temporarily.
Software
SB CS PP.indb 61
Intervention: an action
taken by someone
to make something
different happen.
DEFINITION
Interrupt service routine:
a software routine that
hardware invokes in
response to an interrupt.
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Chapter 4
DEFINITION
Division by zero: a
mathematical calculation
that has no answer, and
one that is automatically
rejected by a computer
for this reason.
There are two different types of interrupt, a software interrupt and a hardware interrupt. Software
interrupts are usually signals sent to an operating system by applications, such as a mathematical
problem like a division by zero or processes attempting to access the same memory location.
Hardware interrupts could be a press of a key on a keyboard, or the click of a mouse button.
. Types of Programming Language,
Translators and Integrated Development Environments (IDEs)
All of the software that we use has to be created and coded by software developers, and the
computer programs that are created have to be translated into signals that can be understood by
a computer system. Here we will examine the processes and sequences that enable this translation
to occur.
.. High-level and Low-Level
Programming Languages
QUICK CHECK
What is the key difference
between a low-level and
high-level programming
language?
In its most basic form, computer language is made up of binary
code, which is a series of s and s. This is called machine code,
and basic instructions that a computer is required to carry out are
written in this language. Machine code is a low-level language,
and this is so named because it is the language of a computer
rather than that of a human.
As machine code is difficult for humans to program in, mainly due to
the difficulty in debugging the code, programmers usually write code in
high-level languages such as Python, JavaScript, C, C++ and Java. They are
called high-level languages because they contain English-like words and terms
that we use in communication and are easier for programmers to understand.
Writing and
debugging code.
All of the programming languages listed above have evolved over a number of years as
programmers develop their knowledge of how to program a computer.
Advantages of low-level language
Programmers who can write programs in
low-level code will be able to create very
effective and efficient programs that tend to
run very quickly.
These programs tend to be specific to the
machine they are programmed on.
Programs written in low-level code will use
both processor capacity and memory very well.
There are likely to be more errors and code is
harder to debug.
Low-level coding can directly change or
manipulate computer hardware.
It is much more challenging for humans to
write low-level coding.
Advantages of high-level language
LINK
See Chapter 1.1.
62
SB CS PP.indb 62
Disadvantages of low-level language
Disadvantages of high-level language
Code is easier to debug.
Code has to be translated into machine code
before it can be executed.
Code is much easier to write and be read by
fellow programmers.
Programs tend to be slower than those
programmed in low-level code.
Programs written in high-level code tend to be
portable, meaning they can run on more than
one type of machine.
Inefficiencies in hardware usage are a common
feature of high-level coding.
Software
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Chapter 4
.. Assembly Language
HELPFUL NOTES
We discussed earlier that machine code is the binary code that is understood by a computer.
Assembly language is a type of programming that sits just above machine code and is a low-level
language that uses mnemonics for its instructions and commands.
A mnemonic is a pattern of letters or ideas that helps a user to remember something.
An example that may be found in assembly language is INP, which is a low-level mnemonic for Input,
and RET, which is a mnemonic for Return.
Activity
Mnemonics help us to
remember complex
information. We
often use them to
remember how to spell
difficult words, where
computers use them to
translate programming
terminology.
What do you think the following mnemonics might represent?
CL
INC
HLT
DEC
WORD ALERT
When a program is written in assembly language, in order for a computer to carry out the programming,
it must first be translated into machine code. An assembler is needed to carry out this task, and this is a
translator application that is usually built into programming software when coding at low-level.
.. Compilers and Interpreters
REFLECT
There are other types of code translation applications that are built into high-level programming
languages, called compilers and interpreters. Both have different characteristics, but a key feature of
these types of translator is to report errors in the code to the programmer.
A programmer will produce a piece of code in a high-level language that is designed for a specific
purpose. It is then important that the code is tested out to see if it does what it is meant to do.
When a compiler is used, it will translate an entire block of code that has been created and will
produce an executable file. When this code then runs, the compiler will produce an error report for
the whole block of code if any errors have been detected. Examples of languages that use compiled
code are C and C++.
When an interpreter is used, it will translate and execute the code that has been written line-byline. Unlike a compiler, which waits until the end of the execution process before reporting errors,
an interpreter will stop the execution of the code when it detects an error. Unlike a compiler,
interpreters do not report syntax errors at the end of the processing. The interpreter will also not
produce an executable file at the end of the process. Examples of languages that use interpreted
code are Python and JavaScript.
Creates more effective
and efficient code
Depending on the
type of programming
language, compilers
and/or interpreters are
used during the code
production process. It can
take hours to compile a
large application.
DEFINITION
Executable: a file that
launches and runs a series
of code when opened.
Slower translation as it is
line-by-line
Code can be kept secret
Takes less time to
translate
Translated: changed into
a different language.
COMPILER
VS INTERPRETER
Things can be hidden
and not detected in
code
Easier for beginners as
errors are easily identified
and corrected
Code is more versatile,
can be viewed on different
systems easily
Figure . Advantages and disadvantages of compilers and interpreters.
Software
SB CS PP.indb 63
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Chapter 4
When programmers are developing code, an interpreter is used for ease of debugging and a
compiler is used to translate the finished program.
WORD ALERT
Debugging: finding
errors or mistakes in code.
.. Integrated Development Environments (IDEs)
An Integrated Development Environment or IDE is an application that
programmers use to test and develop new software. An IDE allows
a programmer to write code in various different programming
languages and will simulate the running of the code so that
development can take place easily.
DEFINITION
Simulate: run a test
version of an application.
An IDE has a number of different features all designed to assist a
programmer in their work.
Code Editor
This part of the environment is called the shell and is a text
editing area. Programmers can write their code in the shell. There
are a number of features built into this part of the IDE that can help
programmers work more efficiently, such as auto-completion, autocorrection and prettyprint.
Auto-Completion
WORD ALERT
When a programmer types in a common function or piece of syntax, the IDE will recognise the
start of the piece of code and suggest or complete it for the programmer. This saves time
while programming.
Syntax: the structure
of not just statements
but also symbols,
punctuation, etc., in a
computing language.
Auto-Correction
Similar to auto-completion, an IDE can detect when an obvious error has been made and will
suggest a correction automatically for the programmer to review. Also built into this feature is
bracket matching, where the IDE will suggest or highlight closing brackets or braces that were
missed out by the programmer.
Prettyprint
ENRICHMENT
There are several
different IDEs that have
been developed for
programmers. Download
one yourself and try
writing a simple program
– you will be surprised at
how easy it is to use!
As discussed in section .., translators provide a vital bridge between high-level and low-level code.
Some IDEs will have a translator built into it, and will be capable of both compiling and interpreting
code written by a programmer. Only the most advanced IDEs support almost all languages.
Run-time Environment
WB
Consolidate your
understanding by
completing Exercise 1,
page 46 in the Workbook.
SB CS PP.indb 64
Translators
When code is compiled or interpreted, the IDE will pinpoint errors, either in a report or on a line-byline basis. It will show the programmer the line number of the error and indicate the type of error
that has been detected.
See section 4.2.3.
64
To make life easier for programmers, most IDEs will format code using indentation and a colour
scheme to make lines and functions easier to spot. Prettyprint also helps programmers to see where
subroutines and loops sit within a larger block of code.
Error Diagnostics
LINK
LINK
Coding in Python –
a high-level language.
This allows a programmer to execute the program one step at a time and is useful to ensure that all
parts of the code are correct before creating the final version of the code.
Software
14.5.21. 14:14
Chapter 4
Let’s Map It
HARDWARE
SOFTWARE
Software and hardware are essential to work together.
SYSTEM
APPLICATION
Allows a
computer to
function
Operating System
Enables a user to interact with the computer.
Allows a
computer to
be used
Applications are required to enable a user to
carry out tasks and work.
Interrupts
All software starts as code
A stop in a process needing a user or program input.
Python
1
2
3
Handled in order
of priority.
Perl
C++
Java
C#
4
Integrated Development Environment
Low- and high-level languages
X
1
2
00110 111001
3
4
Low
5
Code
Editor
if a == 10:
b += 1
High
6
7
8
9
10
Simulation
Translator
Compiler/Interpreter
11
Software
SB CS PP.indb 65
65
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Chapter 4
Let’s Review
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Name two different types of system software.
What are three main features of an operating system?
What is the function of firmware in a computer system?
Complete the sentence. An interrupt is where a piece of software requires...
What are the two different types of interrupt?
Give one example of a software interrupt.
What is the difference between low-level and high-level programming languages?
Why do programmers mainly use high-level languages to write their code?
What is a definition of assembly language?
Name the two types of translators found within programming.
What are the main reasons for choosing between the two types of translators?
Why is it a good thing for a programmer to check their code line-by-line when developing
a program?
13. What does IDE stand for?
14. Name two functions of an IDE.
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Software
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5
The Internet and
Cyber Security
COMPUTER SCIENCE WATCH:
Scan the page to watch a clip on common
types of cyber-crime.
Before watching discuss what you expect
to see or hear.
QUESTIONS
At the end of this chapter, you will be able to:
explain the difference between the internet and the world wide web
understand what is meant by a uniform resource locator (URL)
• What is the difference between the internet
and the world wide web?
• How do we access and use websites
effectively?
• What exactly is digital currency?
• How important is it to keep our computers
safe from cyber-crime?
explain the purpose of the hypertext transfer protocol (HTTP) and the
hypertext transfer protocol secure (HTTPS)
define how a web browser operates and what functions it provides
understand how web pages are found, retrieved and displayed on
your computer
explain what is meant by a cookie and why they are used
understand the concept of a digital currency and how blockchain is
used to keep track of digital currency
understand a range of cyber security threats and the solutions used
to protect data from these threats
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HELPFUL NOTES
The idea of a world wide
web was created by Sir
Tim Berners-Lee, a British
computer scientist. He
decided to gift the idea
to the world and did
not make any money
from the idea. He also
published the world’s first
website in 1990.
One of the greatest developments in computing during the late th century was the introduction
of the internet into our working and home lives. The ability to communicate on a global scale both in
business and leisure has opened up infinite possibilities for users all around the world. However, with
these opportunities also come risks, and with user data increasingly being shared across computer
networks, the need to be safe and secure in our practices online is of paramount importance.
. The Internet and the World Wide Web
It is important to know the difference between the internet and the world wide web. The two terms
are often used interchangeably and wrongly, so it is vital to ensure that the differences are known.
The internet is the enormous network of computers, devices and hardware that are all connected
together as a set of small networks enabling communication between devices to take place. This is
known as infrastructure and represents all of the physical pieces of equipment connected through
service providers to servers all around the world.
The world wide web is the collection of websites and web pages that store the information that
users wish to access. These web pages are stored on servers and users access them using the
internet infrastructure.
.. Uniform Resource Locators
QUICK CHECK
What are the important
pieces of information
that are required for the
receiver’s address on an
envelope when sending a
letter through the post?
Just like houses and homes have unique postal addresses to identify where they are in a given
country or city, websites and web pages also have addresses to help users find them.
These web addresses are called Uniform Resource Locators, or URLs for short. They enable a user to
locate a website easily by typing the URL into the address bar of a web browser. A URL can contain
the protocol, the domain name and the web page/file name.
Every website address has a URL with an equivalent Internet Protocol (IP) address. IP addresses
are made up of numbers and letters and can be very difficult for a user to remember. Refer to
section .. for more information on how IP addresses are matched to website addresses.
Worked Example
A website for a company called My Favourite Cars might have a web page with a web address
of http://myfavouritecars.com. This URL is much easier to remember than the website’s actual IP
address which might be something like .... The URL is better to give to people looking
for the website and is much more memorable than a string of numerical digits.
Just as a postal address has certain items in it that identifies a house, a URL also has identifying
elements. With some or all of these missing, a letter may not arrive at its intended destination.
Postal address example
, City Road
House number and road name
Strickland
Town or city
Walthamshire
County, state or province
England
Country
WE QQ
Postal code
The same is true of a URL. If you only know part of the address, you may not get to the website that
you require.
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These are the elements of a URL:
• protocol
• domain name
• folder structure leading to where the webpage is located
• name of the requested web page
http://clotheswarehouse.com/clothes/shirts
Protocol
http://
Domain name
clotheswarehouse.com
Area within website
clothes/
Web page name
shirts
The whole address then takes a user directly to the part of the website that they wish to view. In the
example above, the website is a business site with a domain name ‘clotheswarehouse.com’ and the
user wishes to access the exact page containing shirts sold by the business. Each element of URL will
be further explained in subsequent sections.
.. Hypertext Transfer Protocol and Hypertext
Transfer Protocol Secure
Data packets are sent around the internet
using different protocols, or rules. The protocol
that web pages use for data transfer is called
hypertext transfer protocol (HTTP) and all
URLs begin with the letters ‘http’.
DEFINITION
Hypertext transfer protocol:
the agreed set of rules
that all computers use for
transmitting files (data)
over the world wide web.
The internet is also capable of providing other
means of data transfer, and different protocols
exist to ensure the correct packets of data reach
their intended destinations. Some of the other
services that the internet provides include
email, file sharing and video streaming.
QUICK CHECK
Data can contain private or sensitive
Keeping your data secure is crucial when using
information, for example, users’ personal
the internet.
information from their online bank accounts,
or payment card details when purchasing an item from a website. When these packets of data are
transmitted across a network, it is vital that this information remains private and secure to prevent
criminals from accessing potentially sensitive information.
What types of information
do you think you might
share when buying an
item online?
When using websites such as online banking or making online purchases, you will notice that, when
completing a transaction, the protocol changes from just hypertext transfer protocol (http) to secure
hypertext transfer protocol (https). This can be noticed by looking at the address bar of the
browser being used to access the web page.
Secure http ensures that a secure connection is made between the two devices engaging in the
transfer of data. The data packets are encrypted before they are transmitted across the network and
are decrypted only when they reach their intended destination. This ensures that criminals such as
hackers would be unable to access the private and confidential information as they would be unable
to decipher the encryption. Any data that was intercepted during this process would be meaningless
to the hacker.
The process of encryption requires the devices at either end of the transfer to use an encryption
key to unscramble the secure data. Websites built with encryption technology will give users the
confidence to carry out these transactions.
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Chapter 5
.. Web Browsers
ENRICHMENT
How have websites
evolved over the years?
Name some things you
can do on a website that
you couldn’t have done
10 years ago.
The main application on a computer that is used to retrieve and display web pages is called a
web browser.
Most web pages are written in a variety of different programming languages, including Hypertext
Markup Language (HTML) and JavaScript, or make use of cascading style sheets (CSS). The job of the
web browser is to translate HTML code from websites and display it to the user as web pages.
Other functions of a web browser are as follows:
Bookmarks
and favourites
This is the ability to store the URLs of your favourite
websites as bookmarks for future reference. Modern
browsers allow you to create quick link buttons to
enable faster access to these websites and cut out the
need to type the URL each time.
Recording
user history
A web browser can store a list of recently viewed web
pages in reverse date and time order. This list will keep
growing from the first use of the browser until it is
cleared by a user.
Allowing the
use of multiple
browsing tabs
Users can open multiple web pages in different tabs,
enabling several sites to be accessed at the same time.
Storing cookies
Cookies are tiny files that are saved to your computer
when you access a website. They can be used to store
your personal preferences or your activity within that
website. Cookies enable websites to display relevant
advertisements that the browser thinks may be of
interest to you, based on your browsing history within
a particular website (see section ..).
Providing tools
for navigation
A web browser contains various icons and buttons at the
top of the window, including a back button, a forward
button and a home button. These navigation buttons
enable a user to move smoothly between all previously
viewed web pages without the need to re-enter
their URLs.
HELPFUL NOTES
A phone book is a
directory containing all
of the listed telephone
numbers for a town.
While web servers do
not contain a book, as it
would be immediately
out of date, the DNS uses
nameservers to locate
different websites.
DEFINITION
Search engine: a webbased tool that is used to
find web pages based on
a given topic or keyword
entered by the user. It
then returns a list of
relevant web pages and
their respective URLs.
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Providing an
address bar
This is where a user can type in the URL for a website
they wish to visit if they know the web address. Modern
browsers will also use the address bar to access the
facilities of a search engine if it does not recognise the
URL immediately.
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.. Locating and Viewing a Web Page
As discussed in sections .. and .., web pages are located on a server somewhere in the world. It
is the job of the web browser to retrieve the web page for the user to view.
It is firstly important to know the URL of the site or page that the user wishes to retrieve. This is
typed into the address bar of the web browser. The browser then makes a request through the user’s
internet service provider (ISP) to locate the web page that has been requested. This process is called
making a Domain Name System (DNS) Query and is like looking up someone’s phone number in a
phone directory.
WB
LINK
Consolidate your
understanding by
completing Exercises 1
and 2, pages 50-53 in the
Workbook.
As we learned in section .., each website has a URL that is linked directly to a unique IP address.
The DNS Query uses the URL that has been entered by the user and looks up the matching IP
address. The IP address then connects the user’s browser to the web server that hosts the site and
retrieves the required website for the user to view from the database.
It is the job of the browser to firstly request the files for the webpage from the DNS and then
translate all of the data that the DNS Query returns into HTML code (see section ..) so that a user
can interact with the website.
.. Cookies
ENRICHMENT
Cookies can be switched
off on websites. What do
you think would change
about your website
browsing if you did so?
Cookies are very small text files that are stored on your computer when you are browsing the world
wide web and websites. They are sent to your computer by the web servers that hold the websites
you are visiting.
Cookies are designed to personalise your user experience while browsing a particular website.
They are generally used to:
• store user preferences on a website
Session
Persistent
cookies are
cookies have
• store login details
temporary cookies that
expiration dates and are
• track user behaviour
are
deleted
when
you
close
stored
in a folder on your
• store items in online shopping carts
your web browser. They provide
computer
until they expire
• help advertisers show relevant
information on your browsing
or
the
user
deletes
them. They
website adverts based on user’s
while you are on that particular
make
websites
appear
to
browsing habits
website and this is not
remember a user on the
There are two different types of cookies
retained once you close
next visit.
that are stored.
your browser.
Worked Example
If you have been recently on a website that sells sunglasses, and you have browsed several
designer brands of sunglasses, the web server of that site will have sent your computer some
cookies that have been designed by those designer brands.
As you then make your way around other websites that contain adverts and advertising space,
those cookies will activate and you will begin to see adverts for designer sunglasses, even if the
site you are viewing has nothing to do with designer sunglasses. This is because your preference
for the designer brands you viewed previously has been stored in their cookies and their cookies
have been accessed in order to find and display an appropriate advert. This is an example of a
persistent cookie in use.
Look out for this next time you are browsing, particularly if you are visiting shopping websites.
Some users consider that browsers collecting data in this way is an invasion of privacy and could
lead to criminal activity like identity theft.
Users do have the choice on a website to disable cookies, however this can affect the user
experience and make browsing less interactive.
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. Digital Currency
HELPFUL NOTES
Bitcoin has been in
existence since 2008
and, although it is not
fully accepted as a
method of payment by
many organisations, it
is considered a highly
efficient way of doing
business due to its low
usage costs.
As the world moves to operate in ever more digital situations, traditional methods of exchanging money
begin to be joined by digital currencies.
A digital currency is one that exists electronically. It is a method of payment, but rather than
exchanging physical coins and bank notes, the payment is made electronically. Payments made
using this cryptocurrency are encrypted. It also operates using what is known as a decentralised
system. This means that there are no central banks to keep track of payments, instead a system
known as a digital ledger is used for cryptocurrency.
The most popular digital currency, or cryptocurrency, is Bitcoin, and these types of financial transactions
are not controlled by the central banks of countries, as they are not issued by these institutions. Other
types of cryptocurrency that are currently in existence are Ethereum, Tether and Litecoin, but these are
worth less than Bitcoin due to the smaller amount of the currency in circulation.
Units of the cryptocurrency are generated by users, also known as ‘miners’, who use the power of their
personal computers to process transactions. The ‘reward’ for doing so is that miners receive some of the
transaction fees involved in the process of payments made.
In order that cryptocurrency transactions are processed fairly and are not obtained dishonestly, there is a
technology that sits behind all transactions called blockchain. Effectively, blockchain is a digital record or
ledger that tracks all cryptocurrency transactions, meaning that each unit of the currency can only ever
be used once by one user.
LINK
WB
Consolidate your
understanding by
completing Exercise 1,
page 53 in the Workbook.
The data behind the cryptocurrency is time-stamped and stored in the blockchain when it is used in
a transaction, and these records cannot be altered by users. This makes cryptocurrency highly secure,
because the way that the data is stored, and the number of bits involved, means that around  billion
combinations would need to be tried in order to fraudulently replicate or fake a unit.
. Cyber Security
User data is highly valuable and highly sought-after by cyber criminals, and just as thieves operate in
the real world, computer users who wish to steal data are operating within the world wide web. Any
risk posed to a computer system from an internet source is considered a cyber threat. By taking steps
to understand what the potential risks are, people and businesses are able to better protect their
systems and data.
ENRICHMENT
Some cyber criminals
have been given jobs by
cyber security companies
because of the skills
that they possess. They
are ethical hackers
who use their skills to
identify security flaws
and make improvement
recommendations. Can
you find an example of
a cyber- criminal who
now uses their skills for
good reasons?
There are various cyber-attacks on our computers and data that users have to protect themselves
against. Some of the attacks are against data and are designed to obtain information from
computers and devices, whereas other attacks can be against human users and are designed to
change behaviour in order to obtain information.
.. Brute-Force Attack
This type of attack is designed to try and obtain a user’s password without their consent. It is like a
thief taking all available keys (not just yours) and trying them all in a door lock one after the other
until the correct key is found. A brute-force attack is where a computer program floods a system with
an enormous number of potential passwords or passcodes and uses trial and error to try and find the
password that matches. Brute-force attacks target weak passwords created by users.
.. Data Interception
When data is being transmitted around a network such as the internet, if it is unencrypted it has
the potential to be intercepted on its way to its intended destination. A cyber criminal could use a
piece of software called a packet sniffer to examine packets of data as they make their way around a
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network. The packet sniffer can then feed the contents back to the criminal, who may be able to use
the information for fraudulent purposes.
.. Distributed Denial of Service (DDoS) Attack
A Distributed Denial of Service (DDoS) attack can happen to a website or web server and is designed
to cause disruption to website owners. A criminal would use software that can ‘force’ thousands of
innocent computers around the world to send a viewing request to a web server. This unofficial
network of recruited computers is known as a botnet and would have likely been infected with some
form of malware (see .. below). The flooding of requests sent to a server will overload it and either
slow the website right down or cause it to go offline altogether.
REFLECT
The biggest DDoS attack to
date took place in February
2020, after Amazon
Web Services (AWS) was
targeted. Can you find
any other high profile
examples of DDoS attacks?
.. Hacking
In simple terms, a hacker is a user who is seeking to gain unauthorised access to a computer system.
Hackers who are attempting to do this for criminal purposes are referred to as black-hat hackers, and
are usually doing so to access, change or damage the data held on the system being hacked.
.. Malicious Code Software (Malware)
Malware (short for malicious software) are pieces of software that have been written and coded with
the intention of causing damage to or stealing data from a computer or system.
There are several different types of malware that criminals have coded and used against users
and systems.
Type of malware
Virus
Description
Like a human virus, this type of malware infects a computer
and then replicates itself to be sent to another computer. This
transmission can happen where infected files are shared via hard
disk drives or sending online.
Trojan horse
A trojan horse is malware that is hidden away in the code of
software that appears to be harmless. Criminals will often hide
trojan horses in illegal or pirate software to obtain user data.
Worm
A worm operates similarly to a virus, however rather than
trying to damage files, it simply replicates itself until the
computer’s resources are used to their maximum capacity and
no further processing can take place, leading to system failure
and crashing.
Spyware
Spyware is a piece of malware that behaves a little bit like a
cookie but, instead of benefitting the user, it actually sends data
back to a criminal. Spyware collects information about online
browsing habits without a user knowing.
Adware
Adware is not always malicious, but almost always involves
installing processes for displaying pop-up adverts while
browsing websites, and will install tracking cookies, often
without user permission.
Ransomware
This type of malware is often quite nasty and makes threats to
users about bad things that will happen to their data unless a
payment of money is made.
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HELPFUL NOTES
A black-hat hacker is
aiming to access systems
for criminal purposes,
whereas a white-hat
hacker is doing the
opposite. Often called
ethical hackers, a whitehat hacker will try to find
security loopholes in a
system and give advice
to the network owners
about how to close them.
REFLECT
The trojan horse malware
is named after the Greek
myth of the same name.
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.. Social Engineering
QUICK CHECK
How is social engineering
different from other forms
of cyber-crime?
This form of cyber-crime is where users are manipulated into behaving in a way that they would not
normally do. There are several different forms of social engineering when it comes to cyber-crime,
but a physical form of the attack is shouldering, when someone attempts to gain information by
looking over your shoulder. This can occur in public places like ATMs or at the cashier when you are
paying for goods. Criminals will attempt to obtain things like Personal Identification Numbers (PINs),
and social engineering is one of the reasons why passwords appear as asterisks onscreen when users
type them in.
.. Pharming
Pharming is a type of social engineering. It is where a user will be sent from a genuine website to
a fake one, with the hope that this goes unnoticed. A user may then be prompted to enter login
details, and this can then be collected by a criminal for use on the genuine site.
Pharming attacks occur when web servers are attacked, and code is inserted into a website that
redirects visitors. These attacks are quite difficult to spot when they occur and require a user to be
vigilant to changes to the URL (for example, how the domain name is spelt) and subtle changes in
the way a site looks.
.. Phishing
WORD ALERT
Spoof: something that is
fake but pretends to be
genuine.
Phishing is a form of social engineering which takes place largely through emails. A criminal will
send an email that looks genuine as if it has come from a business and will often ask a user to click
a link within the email, after an instruction that their data is at risk if they do not comply. Once a
user clicks on a link, it often takes them to a spoof website that is designed to try and obtain login
details. Phishing emails often look convincing but may contain spelling errors and the URL of the
link and the sender’s email address are often giveaways that the email is not genuine. Other features
of phishing emails are that users are generally not referred to by name, where a genuine company
usually would do so.
. Solutions to Cyber Security Issues
One of the most important things that a computer user or network manager must do is protect their
systems from the attacks described above. There are a number of ways in which this is possible, and
users must select the most appropriate method(s) of guarding against cyber-crime.
.. Access Levels
WORD ALERT
Compromise: become
vulnerable or function
less effectively.
DEFINITION
Corrupt: the act of making
data unreliable by errors
or alterations.
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SB CS PP.indb 74
This method of protection is hugely important in organisations where there are lots of users
accessing a network. Users should be assigned different levels of access depending on the role they
have. Administrators of a network have full access and control, and there are several levels of access
going down to basic user access which has only limited rights of usage. This method of protection
ensures that user behaviour can be controlled while they use a computer on a network.
.. Anti-Malware, Anti-Spyware and Anti-Virus
It is essential that networks are regularly protected from harmful or malicious software being
installed. Such software could potentially compromise security of the network, and may allow
criminal activity to occur, including the theft of personal or company data. In extreme cases, such
software could also potentially corrupt data in a network to the point that it becomes unreadable –
this type of corruption is called a virus attack.
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In order to guard against this type of behaviour, a network should have anti-malware and anti-virus
applications installed that protect all devices on the network.
Anti-malware and anti-virus software are constantly scanning documents, files and also incoming
data from the internet. They are designed to detect suspicious activity and files prior to them being
opened or stored and warn the user against opening the files.
If the anti-malware or anti-virus software does detect a file or application that is potentially harmful, it
will immediately quarantine that file away from the rest of the network, preventing it from installing
or multiplying itself to other areas of the network or hard disk drive.
Upon user instructions, the software will then remove and delete the offending malware or
virus. It is important that network managers regularly perform deep file scanning to maintain
the safety of the data that is stored. Users should also be particularly careful when downloading
files and software from the internet and should always check that the downloaded files are from
a reputable source. Additionally, as computer viruses and malware become increasingly more
sophisticated, it becomes vital to update the anti-malware and anti-virus software to the latest
versions, including updating their database of known security threats. Refer to section .. on
automatic software updates.
.. Authentication
A simple and basic method of data
security is to set a password that is only
known to the user in order to access
secure information.
Passwords can be set on many different
websites or devices; mobile telephones
encourage users to set a password
to use the device, and common web
applications require users to create a
password in order to access the features
of the application.
WORD ALERT
Quarantine: to place
into isolation.
Sophisticated: more
complex.
ENRICHMENT
Can you find out the
names of the most recent
viruses that have infected
computers around
the world?
QUICK CHECK
What are the differences
between spyware,
malware and a virus?
It is vitally important that your passwords are not obtained
by unauthorised users.
Passwords should be strong enough to stop criminals from guessing them or hacking into your
personal accounts or applications. A weak password such as a simple seven-character word can be
cracked by a professional hacker in a fraction of a millisecond. An eight-character password would take
on average five hours to crack and a nine-character password would take around five days to discover.
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Passwords should be strong enough to stop criminals from guessing them or hacking into your
personal accounts or applications. A weak password such as a simple seven-character word can be
cracked by a professional hacker in a fraction of a second. An eight-character password would take
on average five hours to crack and a nine-character password would take around five days.
Chapter 5
LINK
WORD ALERT
Alphanumeric: letters
and numbers.
Substitute: exchange for
something different.
LINK
Some applications
will not allow you to
progress beyond the
sign-up stage if the
password you provided
is not strong enough.
Check your password
strength here: http://
howsecureismypassword.
net.
REFLECT
Do you use the same
password for multiple
accounts? How often
have you changed your
password? Are you
the only person who
knows it?
5
PASSWORDS
Some
Inapplications
order to make
will not enable you to
passwords
stronger,
progress beyond the
it sign
is always
initial
up stage ifadvisable
yourto
password
not
use aiscombination
strong enough. You can
of
alpha
(letters)
and
check your password
numeric
characters. If
strength
here: http://
howsecureismypassword.
your password was a
net
 characters less than
 milliseconds
string of nine numbers, and then you
added a letter to those numbers, your
password would be strong enough
that it would take somewhere in
the region of  years to crack the
password. Once you start combining
alphanumeric characters, upper-case
and lower-case letters and special characters
such as question marks and dollar signs, these are
the most secure sorts of password you can set.
 characters
 hours
 characters
 days
One common problem with setting passwords, however, is where users substitute letters in easy
words with similar symbols (see graphic below). Hackers are already aware of this practice and would
make your password
use a combination
of alpharandom
(letters) and
characters.
still be able to crack theseTocombinations
withstronger,
ease. Passwords
that appear
arenumeric
the best
type, If your
was a string of nine numbers, and then you added a letter to those numbers, it would take
however they do becomepassword
less memorable
to a user and can be quite easily forgotten or mistyped.
WORD ALERT
Alphanumeric: letters
and numbers
Substitute: exchange for
something different
somewhere in the region of  years to crack. The most secure passwords combine alphanumeric
characters, capital and lower-case letters and special characters such as question marks and dollar
signs.
A common problem with setting passwords, however, is when
users substitute letters in easy words
oK3<jF8$jT8@iO8*
with similar symbols (see the graphic below). Hackers are already aware of this practice and could
easily crack these combinations. Passwords that appear random are best, however they do become
less memorable, and are easily forgotten or mistyped.
cabbage
Weak undesirable password
Medium undesirable password
Strong password
Passwords should be changed regularly, however, it is unrealistic for
users to change their passwords every few weeks. It is common
Weak
Medium
Strong
practice in most organisations for users
to change their
Password
Password
Password
passwords yearly, but the reality is that many users never
change their password to access popular applications from
Passwords should be changed regularly. It is common practice in most organisations for users to
the first time they have been
set.
Other
examples
of poor
change
their
passwords
every few
months or yearly, but the reality is that many users never change
password security are when
users
set
the
same
password
their password for some applications. It is also poor password security to use the same password for
mostaccounts;
or all your online
once one application is compromised, it could then compromise
for most or all of their online
onceaccounts;
one account
the others.with the same password
is compromised, other accounts
could potentially be compromised as well.
Another way that a user can ensure their passwords are not
18
compromised
is to install a piece of anti-spyware software
on their computer. Spyware is software that can be installed
onto a computer without the knowledge of a user, and usually
happens when a user has been careless or has visited an
insecure website.
Biometric authentication is just
one way of a user authenticating
Spyware runs in the background of your computer, and often
themselves onto a network.
makes processes slow down deliberately, however some of
the more malicious spyware can also track the keys pressed
by a user. The spyware then feeds the information to a criminal using a data collection application
and will gather possible passwords to access private information. Installing a piece of anti-spyware
software will scan regularly for this type of rogue application and remove them.
Passwords are not the only method of authentication that users can undertake to ensure
security of data. Several different methods can be used by websites, businesses, shops and
other transactional devices.
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Method of authentication
Zero login
Unusual
behaviour
can trigger a
system to lock
a user out.
Biometric
authentication
A mobile
device scans a
user’s face to
authenticate
them.
Magnetic stripes
Magnetic
stripe cards
can be used
for hotel
door keys.
Smart cards
Smart cards
have been
used in
banking for
many years.
Features
Zero login is based on the idea that machines
and devices can detect changes in user
behaviour, rather than relying on passwords
to authenticate activity. An example of this
is with mobile devices – software detects
when and where logins occur and check
with a user that it is a genuine attempt to
access an account. Zero login authentication
builds up a picture of a pattern of behaviours
based on usage of various different devices to
ensure that access to software and systems is
granted to the right user.
This is where a user’s human features
are used to grant access to devices or
applications. Common biometric methods of
authentication include fingerprint matching
and retina scanning, and more recently facial
recognition.
Most credit card-sized cards feature a
magnetic stripe on the back of the card. These
stripes can contain up to  characters of data
about a human, such as a name and account
number, and this data is stored magnetically.
The card is then ‘swiped’ through a magnetic
stripe reader and the device is able to
collect the magnetic data from the card
for processing. As long as it matches user
data that is stored, the reading of the stripe
authenticates the user successfully.
This type of authentication is most commonly
found in a credit or bank card. The smart
card has a chip that is read when inserted
into an Electronic Funds Transfer Point of
Sale (EFTPOS) device, containing a chip and
PIN reader. The chip on a card is capable of
holding a lot of information and, when a user
inserts the card into the device, they also
need to enter a four-digit PIN that will enable
a purchase to take place. The device reads
the information from the chip and, if the PIN
matches the information, the card can be
successfully used. This type of authentication
is called two-factor authentication.
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Chapter 5
Method of authentication
Physical tokens
A token can
be used in
conjunction
with a
keycode.
Electronic tokens
A user should
know the
answer to an
electronic
token
question.
HELPFUL NOTES
Operating systems are
almost always released
with security ‘bugs’ in
them as the developers
often rush to get software
out on sale. System
updates usually occur
immediately when the
user runs an operating
system for the first time.
Features
These tokens are often found in the
form of a numerical display device.
When a user is required to authenticate
themselves on a network, a one-time
passcode is generated and sent to
the token. As long as a genuine user
is in possession of the token, they can
enter the passcode on a device and
gain access to a system or network.
The tokens can communicate with
a network server through various
methods, most commonly through a
USB port or Bluetooth.
Similar to physical tokens, electronic
tokens allow users to authenticate
themselves onto a network or system
using virtual methods. An example of
an electronic token could be an answer
to a question that only a genuine user
would know, or a passcode generated
and sent to a trusted device such as
a mobile phone. The passcode can
then be keyed into a network device in
order to authenticate a genuine user.
Sometimes during authentication, a
system will ask for multiple electronic
tokens, for example a password, PIN,
confirmation of email address and a
trusted word.
Activity
For each of the following authentication methods, list the hardware that a system would need in
order for the authentication to work successfully:
1 Physical tokens
2 Smart cards
3 Magnetic stripe
.. Automating Software Updates
This type of protection ensures that applications like operating systems, anti-virus and other
commonly used pieces of software are always operating with the latest version installed. Software
developers will often discover problems in their applications after they have been released and
will develop ‘patches’ that will close potential security loopholes. By enabling automatic updates,
these ‘patches’ will be installed routinely without a need for the user to worry and constantly check
for updates.
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.. Spelling and Tone in Communications
As we learned earlier in section .., phishing emails are a threat to security. However, one thing that
tends to set them apart from other emails is that they tend to have spelling errors and mistakes are
often made by criminals when constructing the emails. As users, if we write our communications
professionally and accurately, the recipient is more likely to believe it is a genuine communication
and respond accordingly.
.. Checking the URL of a Link
Before clicking on any link, whether on a website or in an email, a user should always double check
that it is a genuine link. Usually by hovering over a link, web browsers or email software will enable
you to see the intended destination. If the URL has different words in it other than the name of
the website you expect to visit, or if it is simply an IP address, then the link should be treated with
caution and should not be clicked.
Activity
Can you spot the things in this image that suggest this is a phishing email?
This might be a phishin message and is potentially ussafe. Links and other functionality have been
disabled. Click here to enable functionality (not recommended).
From:
PayPal [service@paypal-australia.com.au
To:
Mr. xyz
Sent: Thu // : AM
Cc:
Subject: Your account has been limited
PayPal
How to restore your Paypal account
Dear PayPal member,
To restore your PayPal account, you’ll need to log in your account.
It’s easy:
. Click the link below to open a secure browser window.
. Confirm that you’re the owner of the account, and then follow the instructions.
PayPal Email ID PP
.. Firewalls
A firewall is a piece of hardware or software that sits between a computer and the internet. Firewalls
carefully look at all incoming and outgoing traffic to a network or a computer. Computer users can
set different rules and criteria for the traffic that the firewall must apply and can be set to block traffic
that doesn’t meet the rules set.
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Chapter 5
Computer users can create a blacklist of websites (websites that cannot be visited) or a whitelist
of websites (a list of the only websites that can be visited) and the firewall will apply these rules to
all network or computer traffic. When the traffic is checked, if it meets the rules or criteria it will be
accepted by the firewall. If the traffic does not meet the rules or criteria that have been set, the
firewall will reject the traffic and halt the data transmission.
.. Privacy Settings
As more online profiles are used to share
content on social media, there is an everincreasing need for users to ensure that
their privacy settings are set correctly.
If no privacy settings are set, then
a user’s content is accessible to
anyone using a particular site or
platform. Privacy settings should
be set to ensure that a user has full
control over who sees and interacts
with data and information online.
.. Proxy Servers
One way of keeping website browsing
activity secure is by using a proxy server.
The user will then view web pages through
a proxy server rather than directly via the
home router. The proxy server sends out the
requests to view a website and sends the information
back to the user. This has the advantage of enabling a
Privacy settings are vital for protecting
against unauthorised access.
user to keep their IP address secret, thus minimising the
opportunities for cyber- criminals to know where data
is being sent to and from. DDoS attacks are therefore much less likely to occur when using a proxy.
Proxy servers can also be used as parental controls on a network, as they can be set up to block
incoming and outgoing web traffic to specified websites.
.. Secure Sockets Layer Security Protocol
SSL is a protocol that is commonly found on websites where financial transactions take place. Any
website that requires users to use a bank card to make a purchase should have secure sockets layer
security. SSL encrypts the connection between the user’s computer and the website that is being
used. All data that is transmitted between the user’s web browser and the web server that hosts
the website is encrypted by the protocol and stays private. The types of data transmitted securely
through the protocol are bank card numbers, login details and passwords.
LINK
WB
Consolidate your
understanding by
completing Exercise 1,
page 54 in the Workbook.
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It is important to check whether a website uses the secure socket layer before carrying out a financial
transaction. If a website has got https:// at the start of the URL, then the site is using SSL and is safe
to transmit personal data. If the URL only has http:// at the start, private data is in danger of being
intercepted, and may not be secure.
An SSL connection is created between a web browser and a web server. This connection is known
as an SSL ‘handshake’, whereby the browser asks the server to identify itself. In order for this
connection to be secure, the web server needs to be certificated. This then provides the appropriate
identification to enable the connection to be made. The encryption information is shared via the
certificate, and the communication then takes place between server and browser, with both pieces
of technology having secured the asymmetrically encrypted connection.
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Let’s Review
1
2
3
4
5




10






What is the difference between the internet and the world wide web?
What do the letters URL stand for?
Http stands for hypertext transfer protocol. What does https mean?
Name three features of web browsing software.
What do the letters DNS stand for?
Describe the process of a DNS Query.
What are the two types of cookies stored when browsing the web.
Name two things a cookie can do while you are browsing the web.
Bitcoin is one type of digital currency. Name another two types.
Explain what blockchain is in terms of digital currency.
Name three different types of cyber-attack that could occur.
What is malware?
What is the difference between pharming and phishing?
Explain what social engineering is.
Explain how enabling software updates can protect user data.
What does a proxy server do?
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CHAPTER
6
Automated and
Emerging
Technologies
COMPUTER SCIENCE WATCH
Scan the page to watch a clip on emerging
technologies in computer science.
Before watching discuss what you expect
to see or hear.
QUESTIONS
• What are the newest technologies coming
into our lives?
At the end of this chapter, you will be able to:
explain how sensors, microprocessors and actuators work together to
create automated systems
• What is an automated system?
• What is a robot?
• How can artificial intelligence change
our lives?
the advantages and disadvantages of using automated systems in
different scenarios
explain what is meant by robotics, including the common characteristics of
a robot
understand the role of robots in different areas of society and the
advantages and disadvantages of this
explain what is meant by artificial intelligence, including the main
characteristics of artificial intelligence and their basic operation
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Chapter 6
WORD ALERT
Automated: machines
carrying out a job that
would otherwise have
been done by humans.
QUICK CHECK
Do you use any
automated systems?
Do you operate them
yourself?
As technologically advances there is less need for humans to carry out some jobs, especially
repetitive tasks. Computers created for specific purposes can automate this type of work, leaving
humans to ensure that nothing goes wrong with the automated processes. This chapter will explore
some of the new ways that computer science has helped to enhance the way we work and live.
. Automated Systems
For a system to be fully automated and operate independently of a human, it combines several
different component parts. The three important components of an automated system are:
• sensors
• a microprocessor
• actuators
A temperature
sensor attached
to a water pipe.
A microprocessor
embedded into a
machine.
An actuator, in
the form of a
piston carrying
out a physical
movement.
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Most sensors are based upon changes in
the environment. For example, a motion
sensor measures change in heat. The sensor
detects the change and sends a message to a
microprocessor (see Chapter  Hardware) to
do something different. The microprocessor
uses the input from the sensors and sends
instructions to other components, such as
actuators.
Actuators turn electrical signals into
physical outputs such as movements.
When all three of these components work
together, automatic instructions become
movements. These movements may be repeated
infinitely, depending on the objective of the
automated system.
LINK
See Chapter 3 Hardware.
DEFINITION
Components: pieces of
equipment in a system.
A motion sensor used in the home.
A microprocessor works mainly on the basis of data comparison. If the data returned by a sensor is
greater, or less than data that is stored, a signal is then sent to an actuator to perform an action.
The action will only stop being carried out when data has normalised and matches again, or after
an amount of time has elapsed.
WORD ALERT
Infinitely: continues
forever, until stopped.
Automated systems exist in many different industries and situations (see Figure .).
Gaming
Artificial intelligence
opponents in games
Lighting
Home control systems
Weather
Airport weather
monitoring systems
Science
Laboratory automation
Agriculture
Crop harvesting
Industry
Packaging of items to be
shipped
Figure . Automated systems.
Table . explores some features of these automated systems and the advantages and disadvantages
of automation for different industries and situations.
Situation
Industry
Scenario
Items in a factory are packed
and packaged by an automated
production line. Sensors are
used to detect the sizes of items,
microprocessors ensure that the
correct packaging materials are
selected and actuators are used to
move the items around to ensure
consistent and accurate packaging
each time.
Advantages
Production is much
faster and the
number of errors are
reduced.
Disadvantages
Fewer job
opportunities
as humans are
replaced by
machinery.
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Situation
Transport
LINK
Agriculture
Automatic harvesting of crops for
supplying to shops and supermarkets.
Sensors detect optimal times for
harvesting based on factors such as
weather conditions, microprocessors
determine exact locations for the harvest
and actuators are used to carry out the
extraction of the goods from the ground.
Faster collection of
the goods.
Weather
Automated monitoring of weather at
airports to help predict poor flying and
landing conditions. Sensors check for
potentially dangerous weather such as
wind, rain, fog or snow, microprocessors
are programmed to issue relevant
warnings as a result of the data
gathered and actuators can activate
emergency systems such as lighting
wherever required.
Information about
the overhead
weather conditions
is fed constantly to
air traffic controllers.
Predictions can
sometimes be
incorrect, for
example if snow is
forecast and does
not arrive.
Gaming
The introduction of artificial intelligence
as opponents in computer games
(see section .). Sensors are built
into gaming environments where
characters interact with human
controllers, microprocessors determine
game outcomes and decisions, and
actuators are activated in controllers to
give haptic feedback, such as vibrations.
The depth of
gaming challenge
is increased
with computergenerated
opponents who
behave in a ‘human’
way.
Decreases real
social interactions
with other humans
and can create an
almost fictional life.
Lighting
Lighting control systems in a house
where routines can be preset based
on behaviours. Sensors can detect
ambient light levels, microprocessors
run routines based on human
requirements and actuators can
activate home equipment.
Systems can be
‘taught’ to react
to environmental
factors, such as
switching lights
on and off when
the conditions are
correct.
Systems can
become complex
as they are different
from traditional
switches. The
lightbulbs and
technology
also tend to be
expensive to
maintain.
Science
Automated laboratory experiments
that can be carried out continuously
over many days. Sensors detect
changes in environmental conditions,
microprocessors can calculate required
alterations to the experimental settings
and actuators can turn on heaters,
coolers or water supplies as required.
Many more
repetitions of
experiments and
reading of data can
take place than
when humans carry
out tests manually.
If something goes
wrong it can be
several hours before
this is discovered,
which could
ruin any results
collected.
ENRICHMENT
SB CS PP.indb 86
Disadvantages
A huge reduction
in road traffic
accidents and
injuries caused by
collisions.
Consolidate your
understanding by
completing Exercise 1,
page 58 in the Workbook.
86
Advantages
Driverless cars can transport goods
and passengers around a city based
on start and end point instructions.
Sensors detect the vehicle proximity
to other objects; microprocessors
control factors like speed and
direction, and actuators are used to
move the steering mechanism.
WB
Can you think of any
other situations where an
automated system has
replaced the work of a
human?
Scenario
Less traffic
congestion.
Potential for more
vehicles on the road
if the technology is
popular.
Automated cars are
very expensive.
Automated vehicles
are large and
Able to cover a large expensive.
distance in a short
Reduced job
amount of time.
opportunities for
humans.
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. Robotics
The term ‘robotics’ means the design, construction and operation of
robots that are used to enhance our working and personal lives.
The different types of robots include those used in factories
on production lines, domestic robots used in and around
the home and airborne robots such as drones.
To be classified as a robot, a system should have the
following characteristics:
• A mechanical structure or framework: a robot
should be a piece of machinery that usually has some
movable parts. It can be large or small.
• Electrical components: a robot should have a
combination of sensors, a microprocessor and actuators. The
robot should also be able to be programmed by a human to carry
out various tasks in a repetitive fashion until complete.
A drone is a popular
type of robot.
The use of robots is increasing all the time, and there are several scenarios where human jobs have
been replaced by robotic equivalents (Figure .).
Domestic
Robotic vacuum cleaners
and lawnmowers will
carry out the jobs with
no human input.
Entertainment
Robotic cameras are used to
position viewing angles.
Medicine
Use of robots to assist in
surgeries where human
hands are unable to
reach.
Industry
Manufacturing Robots
carrying out tasks like
welding.
Agriculture
Robots are used to apply
fertiliser and pesticides
to crops.
Figure . Robotics.
Transport
Robots used in space exploration,
for example the Mars rover.
ENRICHMENT
Can you think of any other
situations where a robot
has replaced the work of a
human?
Table . explores
some of the features
of robotics for different
industries and situations.
Rand the advantages
and disadvantages of
robots.
Robotic arms operating
in a car manufacturing
factory.
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Situation
LINK
Scenario
Advantages
Industry
Manufacturing robots on a
production line in a factory,
putting together cars.
Accuracy in production
is vital, and robots ensure
that every car is put
together the same way
and is identical to all of
the other cars produced.
Fewer job
opportunities as
humans are replaced
by machinery.
Transport
The introduction of robots
into the transport industry
may soon mean that we
have access to self-driving
cars. Space exploration
has increased by sending
robotic vehicles such as
the Mars Rover to other
planets.
Robotic vehicles can get
to places humans are
unable to.
The priority of the
algorithm could be
different in each car.
Some may prioritise
the safety of the driver,
some pay priorities the
safety of pedestrians etc.
This could cause ethical
issues. Automated
technology is expensive,
and could also replace
human jobs.
Agriculture
Crops can be given exact
amounts of fertiliser and
pesticide by robots. This is
particularly useful when the
chemicals are potentially
hazardous to humans.
Accuracy of delivery of
the chemicals is very
important to the success
of farming and crops.
Fewer job opportunities
as humans are
increasingly replaced by
machinery. The robots
can also be expensive.
Medicine
Robots can be used during
surgeries to perform complex
procedures with more
precision, flexibility and
control. They can also be
used to monitor vital life data,
in research and development
such as tissue engineering,
in the replacement of limbs
such as bionic prosthetics
and to simulate certain
medical environments and
tasks for training purposes.
Surgery can take less
time, which improves the
chances of recovery for
the patient.
This technology is
highly expensive
and has to be tested
extensively in research
before it is used on
humans.
Domestic
Traditional household
appliances like vacuum
cleaners and lawnmowers
are being replaced by
robotic versions.
Robots can quickly ‘learn’ This can encourage
the environment. They
a more sedentary
can be programmed to
lifestyle in humans.
work at convenient times.
Entertainment
Robots such as drones
can be used for film and
television programmes, for
example with aerial shots.
Film can be presented in
ways that a human would
not be able to normally see
due to robotic technology.
WB
Consolidate your
understanding by
completing Exercise 1,
page 61 in the Workbook.
REFLECT
Where have you come
across AI systems?
ENRICHMENT
Virtual reality (VR) is
another emerging
technology that is
changing the way we live
our lives. Have you ever
experienced a VR world?
Disadvantages
Fewer job opportunities
as humans are
increasingly replaced
by machinery.
. Artificial Intelligence
Artificial intelligence (AI) is a computer system that thinks like a human, or that simulates human
intelligence.
What sets AI apart from other forms of computer programming is that the system collects enormous
amounts of data from its environment. This data collection is based upon some very specific rules.
The system then uses this data alongside the rules and can reason with it, using ‘what-if’ questions.
An AI system can then learn and change their output by analysing the data constantly.
The two types of AI system you should be aware of are expert systems and machine learning.
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.. Expert Systems
IT applications and systems are sometimes designed with expert procedures and the expertise of
professionals in mind. The systems are designed to imitate a human expert on a specific topic, as if
that person was actually present. These applications often have to be reasonably portable to be used
in the field of expertise.
Chess games
As chess is a highly
strategic game, developers
have designed a system that
allows a human user to play
against a computer.
The computer 'learns' moves
and uses its database to play
against an opponent.
Medical diagnosis
As with patient data, medical
professionals often call on IT to
help diagnose difficult illnesses.
Systems will pose questions that
doctors can use to narrow down
symptoms and make a
diagnosis.
Mineral prospecting
A system which uses sensors
and probes in an area.
The system calculates the probability
of rocks and minerals being present
in the area being explored.
QUICK CHECK
An expert system is any
system that replicates
the decisions taken by
a human expert. Expert
systems have to be
bespoke to particular
circumstances.
Financial
planning
Primarily used by financial
advisors, planning systems can help
to project savings and investments
depending on circumstances.
The system can suggest ways
of saving money or calculate
expenses such as tax based on
information given.
Car engine
fault systems
Used if a car goes wrong
and the solution to fix it is not
immediately obvious.
A computer is plugged into a
special socket of a car and the
system will then use the fault
system to diagnose the
problem.
Plant and aminal
identification
Expert systems for classifying animals
and plants exist, based on a number
of questions that are mainly 'yes' and
'no' or factual answers.
Route scheduling for
delivery vehicles
This is a system used by delivery companies
to ensure its vehicles make the most efficient
journeys and ensure cost effectiveness.
The system will look at the number of parcels to
be delivered, the number of delivery points, the
size of the vehicle and time available, and will
calculate the optimum route.
WB
Table . describes the features of expert systems.
Expert System Feature
Characteristics
User interface
How a user communicates and interacts with the expert system. The
system will often ask questions that require an answer or a button press.
Inference engine
The part of the system that draws upon information from the
knowledge and rules base to produce possible solutions to a problem.
Knowledge base
A collection of information from subject experts.
Rules base
A set of rules that are unable to be broken during problem solving.
Explanation system
The logical reasoning behind the solutions and decisions offered.
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LINK
Consolidate your
understanding by
completing Exercise 1,
page 63 in the Workbook.
DEFINITION
Logical reasoning: a set of
reasonable conclusions
and explanations.
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WORD ALERT
Replicating: creating
as close to a copy of
something as possible.
REFLECT
Think of types of system
that work like a human
brain?
HELPFUL NOTES
The world chess
champion at the time
was Gary Kasparov
from Russia, and he did
manage to beat Deep
Blue eventually!
When an expert system is implemented and used, the user of the system would firstly interact with
the interface. This would be through the answering of questions that would form decisions leading
to further questions, a little bit like a tree diagram. Throughout this, the rules base would prevent the
user from breaking any rules of the system. This is important for safety. The system would use the
answers that were being given to utilise the inference engine. This would begin generating potential
solutions. If the answers generated do not automatically produce an obvious solution, the knowledge
base would enable the user to refer to related information from experts that may potentially provide
a solution. Once a suitable solution has been generated by the expert system, there would then be a
logical explanation to accompany the solution to enable the reasoning behind the results.
.. Machine Learning
Machine learning is a form of AI that allows a computer to perform tasks intelligently and efficiently
by learning from examples.
The system is programmed with an ability to learn or be trained. This happens by inputting data that
can be recalled by the system during development: the more data the system receives, the better it
will be at recognising things later.
Computer scientists program systems for machine learning by replicating some of the functions of
the human brain, such as the nervous system. By producing a system that is as close to a human
brain as possible, this ensures that it can begin to react, adapt and change its responses based on
the input it receives.
One of the most famous AI computers was called Deep Blue – a computer that could play games of
chess against humans. In , Deep Blue was the first computer system to beat the world champion
chess player, within the same time limits as a normal game. Although Deep Blue was not quite the
type of machine learning that we see today, due to restrictions on storage capacity, it paved the way
for much more complex systems as the technology evolved.
A current example of machine learning is where computers are able to suggest tagged names of
people on social media based on the amount of times their previously tagged photographs appear
in timelines. The same process happens with places too, and machine learning AI on social media
uses previously learned input to suggest place locations to add to photographs.
A supercomputer capable of machine learning has enormous processing power.
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Chapter 6
Let’s Map It
Microprocessor
Sensors
Decisions made
AUTOMATED
SYSTEMS
Processing
instructions sent
Automated system
Activaters
Movements
Science
Industry
Weather
Transport
Gaming
Agriculture
Lighting
ROBOTICS
COMPUTERS
THAT LEARN
• Industrial
• Transport
• Medicine
• Domestic
• Agriculture
• Entertainment
ARTIFICIAL
INTELLIGENCE
Chess your
move...
Expert system
Machine learning
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Let’s Review
1. What are the three components of an automated system?
2. What does an actuator do?
3. Apart from driverless cars, describe an example of an automated system that exists in the world
of transport.
4. A disadvantage of automated systems in gaming are that they can reduce social interactions
with other humans. Think of another disadvantage?
5. Name a type of robot.
6. What are the characteristics of a robot?
7. Robots are sometimes used for medical purposes during operations. Think of another example of
a robot used in medicine?
8. An advantage of a robot for domestic or home use is that they carry out jobs accurately. Think of
another advantage?
9. What do the letters AI stand for?
10. What are the two types of AI?
11. In your own words, and using the vocabulary knowledge base, rule base, inference engine and
interface, describe how translation software works.
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CHAPTER
7
Algorithm Design
and Problem Solving
COMPUTER SCIENCE WATCH
Scan the page to watch a clip on
algorithms.
Before watching discuss what you expect
to see or hear.
QUESTIONS
• How is a problem solved through
programming?
At the end of this chapter, you will be able to:
understand the different stages of the program development cycle,
including the tasks performed at each stage
• What stages does a problem go through to
become a solution?
• What are algorithms?
• How can algorithms help developers to
create programs?
explain the purpose of a given algorithm
understand how a linear search and a bubble sort are performed
understand how totalling, counting and finding values are performed
understand the importance of validation checks, including how a
range of different validation checks are used
understand the importance of verification checks, including visual
checks and double entry checks
understand how to choose suitable test data to test an algorithm
understand how to complete a trace table
write, amend and identify errors in an algorithm for a given problem
or scenario
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Chapter 7
WORD ALERT
Algorithm: a set of rules
or instructions for solving
a problem.
For the purposes of exemplification of coding, the programming language selected is Python.
There are a few examples where an alternative language has been used to give an example
and, where this is different from Python, this has been stated. The reasons for the differences is
that some of the examples in the IGCSE syllabus are not present within Python, so alternative
languages have been used to demonstrate these features. Python does not deal with arrays or
case statements and, in their place, the list and nested if functions are used instead.
In this chapter we are going to explore algorithms and how they are used by programmers – in
particular to solve problems. It is important to understand why algorithms are important, so that
they can be used for different ways of solving a problem, and also how to structure them correctly.
However, we must begin by looking at the program development life cycle and the process
programmers go through when creating a solution to a new problem.
. The Program Development Life Cycle
When creating any new program, developers follow a process called the program development life
cycle. This consists of four stages: analysis, design, coding and testing.
ENRICHMENT
Do you think critical
thinking skills are
important for asking the
client the right questions
and gathering maximum
details?
WORD ALERT
Perspective: a particular
way of thinking about
something.
UnPC: an exhaustive
discussion to solve
problems or generate
ideas.
Negotiations: a
discussion to produce a
settlement or agreement.
It is a cycle and not a linear process because after developing the software it is often necessary to go
back to the start of the process again if something has been discovered during development.
.. Analysis
Stage  Analysis
A system process begins with analysing or understanding requirements from the client’s
perspective. Here, the client can be an organisation or the end user. The analysis stage may include
several UnPC sessions, negotiations, data collection and information exchange. It is very important
to allocate time to this – without a thorough understanding of the client’s requirements the entire
process can become endless repetitions and corrections.
Stage  Requirements
Ideally, after the initial discussions an analyst will sketch out the requirements. This may not always
be practical if the program managers have limited resources and certain strengths and weaknesses
in their team. To make the tasks achievable and avoid any potential risks and doubts, it is always
good practice in the system process to conduct a feasibility study and create a feasibility study
report. This highlights problems and possible solutions.
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Chapter 7
Stage  Abstraction and Decomposition
The next stage of the analysis is to carry out abstraction and decomposition of the requirements.
These are of two of the key elements of computational thinking – breaking down a complicated
problem and developing a potential solution to it. Abstraction is the process of selecting the
information in a problem and focusing only on the important parts of that information. During
abstraction, any detail that is irrelevant to the problem is ignored.
Decomposition is breaking down a complex problem into small manageable pieces. A problem
becomes a series of small tasks that can be handled first individually and then collectively as part
of the bigger program.
DEFINITION
Computational thinking:
breaking down a problem
into smaller sub-problems
to solve them.
Worked Example
Abstraction
Problem: A person wishes to make a cup of tea.
Information obtained: teabags, milk, sugar, white mug, water, kettle, teapot.
Abstracted information: we can ignore the colour of the mug as this is not relevant to this
particular problem.
Worked Example
Decomposition
Problem: A person wishes to make a cup of tea.
This complex problem can be broken down into four smaller problems: water, combine,
personalise and serve.
Decomposed problem:
• Water: fill the kettle with water and heat it until it reaches boiling point.
• Combine: add the water to a teabag in either a teapot or mug and leave for a set time.
• Personalise: remove teabag from water, pour tea into a mug, and add the sugar and milk
to taste.
• Serve: stir the tea and drink it from the mug.
.. Design
In the design phase, the developers of the program will continue the decomposition phase from the
analysis and begin to draw up visuals of the end product. This will include structure diagrams that
help to visualise the end goal. The coding required to make the visual representations happen will
be started at this point.
The developers will create flowcharts that show how a program’s decomposed parts will run,
including any decisions or inputs that are needed. The programmers will then begin to develop
pseudocode that enables the complex problems and instructions to be read in plain English.
Pseudocode is an excellent way to check that the instructions make sense prior to the
coding process.
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WORD ALERT
Visualise: to be able to
see a prototype of an idea.
WB
LINK
Consolidate your
understanding by
completing Exercise 1,
page 66 in the Workbook.
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Worked Example
Flowcharts
Problem: Making a cup of tea – the water stage.
A flowchart for this particular decomposed problem might look like this.
NO
HELPFUL NOTES
A test plan includes:
• a list of the tests planned
YES
• the data to be used in
the test
• the expected outcomes
The steps are written out and the appropriate decisions are contained within the flow.
• the purpose of each test
• the type of tests to be
performed
WORD ALERT
Comprise: include, be
made up of.
.. Coding and iterative testing
This is sometimes known as the implementation stage. The programmers work on the design
modules, such as input, output and processes, and write the code to make each part of the program
functional. The programming is then linked together as a complete solution. A testing strategy is
planned by analysts and the test plan will comprise details of all the programs to be tested.
.. Testing
DEFINITION
Test strategy: test plans for
testing the system.
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Testing every part of the programming requires a test strategy. First, the entire system is divided into
small sections that are tested for input, output and validation rules. Test data is used for all of the tests
to be carried out. Testing each part of the code individually is known as unit testing, and integration
testing is used when this code is all combined to form a program. The testing team reports any errors
to the programmers and the testing is repeated until there are no errors found in the system.
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Chapter 7
. Computer Systems
LINK
As we learned in Chapter , all computer systems require an input, some processing and an output.
Also linked to this processing is storage, which enables data to be used as and when required.
All computer systems that operate are made up of subsystems, which can have further subsystems
within them. These are smaller processes that are vital for the bigger system.
We can apply what we know about systems to programs. Each problem to be solved by a program
can also be decomposed into its component parts. For every problem, the design stage must
consider the inputs required, the processing required and the resultant outputs.
Chapter 3: Hardware.
QUICK CHECK
What are the three ways
designers can plan a
solution to a problem?
Programmers can employ a combination of different methods to plan solutions to problems.
Pseudocode, structure diagrams and flowcharts are often used in combination to design
these solutions.
Flowchart
Pseudocode
Structure diagram
Pour the water into the kettle.
Plug the kettle in.
Switch the plug on at the wall.
Turn the kettle on.
Check to see if the water is boiling.
If the water isn’t boiling,
check the electricity.
If the water is boiling, wait for
a number of seconds.
If the water has not yet reached
boiling point, keep waiting.
If the water has reached boiling point,
turn off the kettle and pour the water.
NO
YES
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.. Flowcharts
In a flowchart, a set of standard symbols are used to identify different parts of the data flow. The most
common symbols are shown here.
Symbol example
ENRICHMENT
Draw a flowchart for a
simple procedure, for
example how to brush
your teeth?
Terminator
Use
This symbol represents the
start and end points of a
sequence of data.
This symbol represents an
instruction.
Process
This symbol represents a
decision, that is a yes or no
answer.
Decision
Input or output
This symbol represents an
input received or an output
sent by a system.
This symbol represents
connections between the
other symbols and the flow
of data around the system.
Flow direction
This symbol represents a
smaller procedure running
within the larger program.
Subroutine
DEFINITION
Pseudocode: a version
of programmable code
written in standard
English.
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.. Pseudocode
Another way that data flow can be represented at the design stage is by using pseudocode. This is
a useful way of designing solutions as it can be written in a way that doesn’t require exact use of the
same syntax as any particular programming language.
Pseudocode at this stage doesn’t rely on which language the program is to be written in and can be
structured in a way that anyone can understand the procedure or flow of data.
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Chapter 7
For example, writing some pseudocode for a procedure for starting a new game might look like this:
IF Lives = 0
REFLECT
THEN
Try writing some
pseudocode to describe
your decisions about
eating.
End Game
Output “Game Over!”
ELSE restart the level
ENDIF
WB
.. Structure Diagrams
Structure diagrams are another way of representing data flow in diagram form. They are different
from flowcharts as they display the different levels of detail within a set of decomposed problems.
LINK
Consolidate your
understanding by
completing Exercise 4,
page 74 in the Workbook.
The problems are sometimes broken down into smaller problems, or subsystems, and they are
represented in a tree diagram, with the big picture at the top.
In our tea making example, the structure diagram may look like this:
As all of these subsystems happen one after another, this diagram does not have a hierarchical
structure, however if these subsystems were decomposed even further, then there may be another
level or levels of structure.
Just like flow charts, there are a set of pre-defined symbols that go into a structure diagram.
Symbol example
Use
This symbol represents an
instruction and will need to be
programmed.
Process
This symbol represents that some
sort of iteration is occurring and
will need to be coded as such.
Loop
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Symbol example
Selection
Use
This symbol represents a
common procedure that is likely
to already exist in a programming
language’s library.
This symbol represents a
selection and that there will be
different outcomes.
REFLECT
Think about the last
algorithm you followed,
what was the end goal?
WORD ALERT
Pictorially: in the form of
a diagram.
Pre-defined function
. Algorithms
An algorithm is a set of instructions or rules to follow step-by-step to solve a problem. A flat-pack
piece of furniture usually comes with an instruction manual that details a set order on how to
assemble the item. This is a type of algorithm.
As we learned earlier in the chapter, an algorithm can be represented both pictorially and in textual
form. There are often multiple ways of solving a problem and exploring all of these at the design
stage is beneficial.
When designing an algorithm, have the end result in mind. A programmer needs to understand the
goal and look at the stages involved in achieving that goal.
• Inputs: What are the inputs to the problem?
• Outputs: What will the outputs look like?
• Order: In what order do things need to be carried out?
• Decisions: What decisions will be made while solving the problem?
• Repetition: Are any of the stages repeated?
HELPFUL NOTES
Worked Example
When designing an
algorithm, always consider
the extent of the problem
and the end result.
Algorithm design
An end user needs a program that calculates shipping costs for items sold, and different costs
apply depending on where things are being posted to. The end goal is the correct
posting costs.
The stages of the problem are as follows:
ENRICHMENT
It is important to
remember that flowcharts
and pseudocode have
to be used together to
design an algorithm.
Solutions can be unclear if
either are missing.
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• sizes of the items
• cost of preparing the item for posting
• location of posting destination
• cost of posting calculated: size + packaging + destination rate
A programmer would take all this information, abstract and decompose the problem, and then
create appropriate flow charts, pseudocode and structure diagrams to come up with the most
efficient solution based on the information gathered.
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Chapter 7
Activity
Design an algorithm that helps a bus or train system determine the correct fare to charge a
passenger. (Hint, passengers could be adults or concession fares, children or senior citizens).
Draw a flowchart and write some pseudocode to show your working.
WB
LINK
Consolidate your
understanding by
completing the Exercises
1-3 from pages 66-73 in
the Workbook.
. Solution Methods
The concept of algorithmic thinking has been around for a long time, since computers have
existed. So, there have been many algorithms designed that have become common in a variety of
programming languages. In particular, algorithms can search and sort data, find totals and count
data, and also carry out functional operations such as finding the maximum, minimum and
average values.
.. Linear Search
As its name suggests, this type of search means that all items of data in a set are looked at until
the program matches the piece of data it is looking for. Once this match is obtained, the search is
completed.
We can try to understand linear search by looking at this table of game scores.
Position









Scores









If a program was required to search for a specific score of , a linear search would begin at position
, and check the score. This score is  and is not a match, so the search moves on to position 
(no match), then position  (no match), position  (no match) and then reaches position , where a
match for  is found. The linear search then ends.
This type of search is not the most efficient method of finding a match of data, however it will work
on any data set.
.. Bubble Sort
A bubble sort is another standard solution algorithm, and this is used for turning a data set from an
unordered set into an ordered one.
A bubble sort is based upon the idea of swapping adjacent items in a data set until the set is in
the desired order. A bubble sort becomes increasingly slow as the number of items in the data set
increases, as it is based upon making comparisons.
Each time a comparison is run through the data set, this is known as a pass. The sort ends when a
pass is made through the data and no swaps are carried out.
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REFLECT
Linear searches are quite
inefficient in nature. Why
do you think this is the
case?
ENRICHMENT
A bubble sort is only
efficient with a small data
set. How would you sort a
larger data set?
WORD ALERT
Adjacent: the item next
to another item.
Comparisons: checking
one item against another
and looking for differences
or similarities.
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Worked Example
A bubble sort
A data set consists of the following unordered game scores, and an algorithm is required to
order this list from smallest to largest:
Position




Scores




Pass one
The value contained in position  () is smaller than position  (), so nothing changes at this
stage of the pass. The sort moves to the next adjacent position. This time the value in position
 () is larger than position  (), so these two items are swapped.
Position




Scores




The next position, position  is considered. The value here () is larger than the value in
position  (), and so these two items are swapped.
Position




Scores




This is the end of the first pass, but the order still may not be correct.
Pass two
A second pass now takes place. The value in item  () is larger than the value of item  () so
these are swapped.
Position




Scores




The value in position  () is larger than position  (), so these are also swapped.
Position




Scores




The value of position  is smaller than position , so no further swaps are made. This is the end
of pass two.
Pass three
The sort then begins a third pass. The value in position  () is larger than position  (), so
these items are swapped.
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Chapter 7
Position




Scores




QUICK CHECK
Position  is smaller than position , so no swap is made. Position  is smaller than position , so
again no swap is made. This is the end of pass three.
What is meant by a pass
when sorting?
Pass four
A fourth pass is then carried out, but no further swaps are required. This is the end of the sort,
and because no swaps occurred in the fourth pass, the algorithm now knows that the data set is
in the desired order.
As you can see in this example, a bubble sort on a large data set would take a comparatively
long time to carry out and would be highly inefficient.
Activity
How many passes would be required to sort the following data set from smallest to largest using a
bubble sort?
Position





Scores





.. Totalling and Counting
REFLECT
• Totalling: a common algorithm used to add one number to an existing stored number. For
example, you might wish to add up the number of different objects collected by a player in
a game.
Why is a final pass carried
out in a bubble sort even
when nothing changes?
• Counting: keeping a check on how many times a program has repeated a procedure in a loop.
For example, you might wish to count the number of attempts at a level in a game.
.. Standard methods of solution
There are also some common functions that can be performed as algorithms. This may be useful
during the problem-solving process.
HELPFUL NOTES
A count is a fairly standard
feature of most computer
games. Counting is used
for lives, levels and health.
• MAXIMUM: Within a specific data set, this standard algorithm can identify and return the largest
number in the set.
• MINIMUM: Within a specific data set, this standard algorithm can identify and return the smallest
number in the set.
• AVERAGE: Within a specific data set, this standard algorithm can take all the values in the data set
and return an average value of all data.
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ENRICHMENT
Can you find any other
common functions in
programming languages?
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HELPFUL NOTES
Data validation checks
include presence,
range, length, format,
consistency and type.
DEFINITION
Validation: the process
that helps the system
know the data entered
is correct.
Validation check: testing
for validations.
. Data Validation and Verification
When creating coding for a new system, it is important that a programmer considers all the input of
data that will be coming into the program. Validation checks on data are therefore essential to the
correct working of the program, and these checks ensure inputted data follow the rules. If the data
does not follow the rules set by the checks, the data will be rejected by the program.
.. Validation
There are several types of validation check that a programmer can implement into their code
where user input is required.
Type of
validation
Purpose
Example usage
Coded example
Range check
This checks for data
input that falls within
a range, and can
apply to numbers,
dates and characters.
A date of birth is
required and the
program requires a
user to be older than
age .
if age in range (0,12):
print( “you are not old enough
to continue”)
else:
print(“you may continue”)
Length
check
This checks whether
an input is too long
or too short.
A password or
passcode is required
and must be a
particular length.
pw = input(“Type your
password:”
if (len(pw)<5 or len(pw)>10):
print(“Your password is not
valid”)
else:
print(“Your password is the
correct length”)
Type check
This checks whether
an input is the
correct type of data,
such as text or a
number.
An age is required
in numbers and any
other type of data is
rejected.
type(object)
Presence
check
This checks whether
an input has been
made or not, and will
not allow a process
to continue until
something has been
entered.
The quantity of
items ordered was
required to make
a stock system
calculate a total.
quant = input(“Please enter
number of required items:”)
while len(quant) == 0:
quant = input(“Please
enter number of required
items:”)
Format
check
This checks to see
if data has been
entered in the
correct format for
the input.
A date is required
in DD/MM/YYYY
format.
day = input(“Please enter the
day of your date of birth:”)
if day in range (1,31)
print(“next”)
else:
print(“please re-enter the
day”)
repeat for month and year
Check digit
This checks for
the final digit in a
code of numbers
and is calculated
mathematically from
all of the other digits
in the code.
A number from a
barcode needs to be
stored.
num1 = input(“please enter
number 1:”)
num2 = input(“please enter
number 2:”)
num3 = input(“please enter
number 3:”)
sum = float(num1)+float(num2)
+float(num3)
print(“Digit is” (sum))
ENRICHMENT
Validation checks
sometimes display a
message known as a
prompt box to let the
user know the data
entered is not valid.
REFLECT
Different form fields can
have different validation
checks based on the
type of data entered. Can
you suggest a validation
check for entering an
appropriate password?
QUICK CHECK
List the different data
validation checks.
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.. Verification
REFLECT
It is one thing having a system validate data for input errors, but it is another thing checking to see if
the data entered is meaningful and correct. Even with a variety of the validation rules applied from
the table above, wrong data could still be entered.
There are two methods of verifying data that has been entered:
Visual checks have to be
carried out by humans,
and this increases the cost
of this part of verification
• Double entry: The same data is entered twice and the first entry is checked against the second
one. For example, a system requires a password and asks the user to enter it a second time to
ensure it is an absolute match.
• Visual check: A human check for erroneous data that has been entered into a system and trying
to spot obvious errors or mistyping.
. Testing
Testing every part of the program requires a test strategy. First, the entire program is divided into
procedures that are tested for input, output and validation rules. The testing analysts report any
errors to the programmers and the testing is repeated until there are no errors found in the system.
There are four types of testing data:
• normal data
• extreme data
• abnormal data
• boundary data
Consider the following scenario. The qualifying age for an exam is between  and  years.
The different types of testing values for this are shown in the table.
Type of testing data
Description
Example
Normal data
The data that is entered normally as
per the expected outcomes.
The values will be , , , , ,
, , .
Extreme data
This data includes the extreme
values of the normal range given.
The values will be , .
Abnormal data
This data is outside the limits of the
acceptable data given.
The values will be , , male,
female.
Boundary data
This data includes the extreme
values of the normal range given
and the corresponding smallest/
largest rejected value.
The values will be , , and the
rejected boundary data would be
 and .
. Trace Tables
Before coding can complete the testing phase, it is important to put algorithms through a ‘dry run’ to
ensure that they all work as intended.
This is carried out by producing a trace table, which enables a programmer to work through the
code on paper, line-by-line, to check where variables, selection, sequencing and iteration take place.
The trace table also allows a programmer to check the results of the processing and to see what
should be output at any given point in the code.
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Chapter 7
It is also important to try to list all of the possible user inputs into a program when designing a trace table.
Worked Example
A trace table
Consider the following simple program that iterates four times through an addition of  to a
starting number:
1
Number = 5
2
PRINT Number
3
FOR x FROM 1 TO 4
4
Number = Number + 3
5
PRINT Number
6
PRINT “Complete!”
The trace table for this program would look like this:
Line number
Number


x






















Output





Complete!
Each time the variables change, their values are listed in the table. The trace then iterates back
through the loop as many times as has been programmed.
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Chapter 7
Activity
Draw out a trace table for the following program:
1
Number = 18
2
PRINT Number
3
FOR y FROM 1 TO 5
4
Number = Number + 7
5
PRINT Number
6
LINK
See Chapter 8
Programming.
PRINT “Done”
Your table will require the following headings:
Line number
Number
y
Output
. Error Checking and Correction
Two of the most common errors that can occur when writing programs are syntax errors and
logic errors.
• Syntax error: some of the code goes against the rules of the language that has been written for
the program. This can be a misspelling of a common word, omitting brackets or trying to call a
variable before it has been declared.
• Logic error: a program behaves unexpectedly and produces unusual results. This type of error can
occur when logical or Boolean operators are not used in the correct manner, putting a program
accidentally into an infinite loop or using variable names wrongly.
The key difference is that with a syntax error the program will not run at all, whereas with a logic error
the program will run but it is likely to run incorrectly and not work as expected.
Most programming
languages will have
syntax correction built in
and will even identify the
line where an error has
been found.
Syntax errors
Each of these lines of code contains a syntax error:
STRAT
2
POINT(“hello world”)
3
INPUT(“What is your age: “
Boolean: where a variable
can have one of two
values, true or false.
HELPFUL NOTES
Worked Example
1
DEFINITION
• Start has been spelt incorrectly in the first line.
• Point should be print in line .
• Line  has had a bracket opened but not closed – a close bracket should be added at the end
of the question.
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Chapter 7
LINK
Logic errors
This program was written to determine whether a cheap travel fare can be applied for a young person.
WB
Consolidate your
understanding by
completing Exercise 5,
page 78 in the Workbook.
The program has been written in Python for the purposes of looking at the errors in detail.
1
Age = INPUT(“How old are you: “))
2
IF Age = 13:
3
PRINT(“child fare”)
4
ELSE
5
IF Age >=12:
6
PRINT(“child fare”)
This code will work when it runs, however there are several logic errors:
• In line , the program will respond if someone is exactly  and not  or under.
• In line , the program states that a child fare is payable if the passenger is greater than or
equal to  – this is incorrect and should be re-coded.
• The program also doesn’t enable an outcome for someone who isn’t a child passenger.
The program should look like this:
QUICK CHECK
What are the three types
of design documentation
needed to create an
algorithm?
1
age = int(input(“How old are you: “))
2
if age <= 13:
3
4
5
print(“child fare”)
else:
print(“adult fare”)
. Writing Algorithms
It is now your turn to create some algorithms. Work through the activities below. For each scenario,
create a flowchart and pseudocode, to solve the problem.
Activity
LINK
WB
Consolidate your
understanding by
completing the Exercises
1-3 from pages 66-73 in
the Workbook .
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Design, document and code a solution to the following three problems:
A A cinema is looking for a system which only allows customers to see films that are appropriate to
their age. Using a date of birth, a system must determine whether a customer can buy tickets for
a Universal (U) film, a Parental Guidance (PG) film, a  rated film, a  rated film or an  rated film.
B A game needs to store the top ten scores for a level to be able to run a monthly competition.
Once a month ends, the top score from each month must be added to a table that shows all of
the top monthly scores in a year.
C A car hire company wishes to only hire Category  vehicles to customers who are over the age
of , have a clean driving licence and have been driving for at least  years. They wish to hire
Category  vehicles to customers who are over , may not have a clean driving licence and have
been driving for at least  years. They wish to hire Category  vehicles to customers who are over
, may not have a clean licence and have been driving for at least  years. They do not wish to
hire any vehicles to customers below the age of , regardless of their driving licence status or
how many years driving of experience they have.
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Chapter 7
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Chapter 7
Let’s Review
1
2
3
4
What are the four stages of the program development life cycle?
What is abstraction?
What is decomposition?
In a flowchart, what is this symbol used to represent?
5
Pseudocode uses only the syntax from a programming language to design a solution to a
problem. True or false?
What is the difference between a flowchart and a structure diagram?
Why is a linear search an inefficient way of searching through data?
What is an unordered data set?
Describe how a bubble sort works.
Name three types of data validation.
Visual checking is one form of data verification. Name the other type.
Explain the purpose of testing a program.
What is extreme data when testing a program?
What is the purpose of a trace table?
What type of error would be present if a common word had been spelt incorrectly?
Write an example of a logic error in a line of code.
6
7
8
9
10
11
12
13
14
15
16
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CHAPTER
8
Programming
COMPUTER SCIENCE WATCH
Scan the page to watch a clip on Python
programming.
Before watching discuss what you expect
to see or hear.
QUESTIONS
• What are the key concepts of programming?
• What are the different types of data you
can work with when coding?
At the end of this chapter, you will be able to:
understand how to use variables and constants
• How can you write code to do mathematics?
• What sort of programming goes into
a game?
understand how to use different data types
understand how to use sequence, selection and iteration
understand how to use totalling and counting methods
understand how to use string handling methods
understand how to use procedures and functions
understand how to use a range of library routines
understand how to create maintainable programmes
understand how to use both D and D arrays
understand how to use file handling methods
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Chapter 8
In Chapter  we looked at the importance of algorithms when solving computer problems. Computers
put these algorithms into action while using a programming language. When programming a piece
of software, algorithms and instructions can be communicated to a computer’s hardware to carry out
the requirements of a user.
It is important to note that there are many programming languages and, just like different spoken languages
from around the world, each one has its own set of unique words and rules. Even though some ideas
seem the same between different languages, the way of achieving the outcome can be quite different.
For the purposes of exemplification of coding, the programming language selected is Python.
There are a few examples where an alternative language has been used to give an example
and, where this is different from Python, this has been stated. The reasons for the differences is
that some of the examples in the IGCSE syllabus are not present within Python, so alternative
languages have been used to demonstrate these features. Python does not deal with arrays or
case statements and, in their place, the list and nested if functions are used instead.
QUICK CHECK
How much programming
have you done? What
languages have you
programmed? How
confident are you
with this?
. Programming Concepts
.. Variables and Constants
Data can be constant or variable when used in a program. A variable piece of data can be changed
in some way, either by the user or the program. This data has to be declared by a programmer before
it can be used in code.
LINK
WB
Consolidate your
understanding by
completing the Exercises
1-2 from pages 91-92 in
the Workbook.
Declaring a constant or variable means that the type of data is defined, and an initial value for the
variable or constant is set. Variables do not have to have an initial value, but it is often useful. For
some programming languages, data types of constants and variables must be specifically declared
to be used in programming, however in others, such as Python and JavaScript, this is not the case.
Constants stay the same every time a program is run or executed. They do not change their value. A good
example of a declared constant might be an amount of time that something should take in a game.
Variables are items of data that are expected to change during the program’s operation, usually
because of a question that has been asked or activities within the program. A good example of a
variable would be the high score for a game. Variables are a location within the computer’s memory,
and the data associated with the variable is stored in this location. The variable therefore needs to be
given a name by which it can be found during the program’s execution.
.. Basic data types
There are five basic data types that programmers use when creating code. These are used to declare
variables or constants.
Data type
DEFINITION
Floating-point: a number
in programming that
contains a decimal point,
and the decimal point
can ‘float’ in different
places to help with
handling large numbers.
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Definition
Example
Integer
This is either a positive or negative whole number.

Real
This is a decimal number and can also be used
to store integers. It is also known as the float
(referring to floating-point).
.
Char
A data type used for holding a single character,
which could be a letter, number or symbol.
£
String
A combination of letters, numbers and symbols
held together as one piece of data.
PROGRAM
Boolean
A data type returning a True or False value, or  for
On and  for Off.
FALSE
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Chapter 8
.. Input and Output
Input and output are another two important programming concepts, and refer to communication
between a program and a human user.
Input
The input is used where some information is required by the program, often from a user. The input is
used to prompt the user to enter some data. This type of input also requires an instruction to tell the
user what sort of data they need to enter. Input can also come from within a program itself, although
this is often considered to be an inefficient way of coding. Another way of obtaining input is from an
external file that is linked to the program.
WORD ALERT
Inefficient: not the
best or fastest way of
achieving a goal.
Output
The output is where information is communicated back to the user as a result of the input. This is
usually done using the print function. This statement usually gives the user some information about
the result they are about to see, and then the results of any calculations carried out on the variables
or constants are displayed.
Worked Example
WB
LINK
Consolidate your
understanding by
completing Exercise 3,
page 94 in the Workbook.
Here is an example of some Python code for a program that calculates the area of a circle.
Mathematics and geometry show us we can calculate the area of a circle with this formula:
πr2
The symbol π (pi) is a constant and is equal to approximately . when rounded. To find the
area of a circle we first need to know its radius, r. Most programming languages have a pi
constant already built into their library of functions.
If we know that the radius of the circle is 5, we could write this Python code to calculate the area:
FROM math IMPORT pi
r = 5
PRINT (“The area of the circle with radius ” +
str(r) + “ is ” + str(pi * r**2))
The circle with a radius of  has been hard coded into this program and is stored as a constant.
However, it would be much more useful for the programming to be able to accept a user input
for the radius and store it as a variable, so that a circle of any radius could be calculated.
We could therefore consider the following adjustment to the Python code above:
FROM math IMPORT pi
r = float(input (“What is the radius of the circle : “))
PRINT (“The area of the circle with radius ” +
str(r) + “ is ” + str(pi * r**2))
This time the user is prompted to enter the radius, and the program uses that data to make the
calculation.
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Chapter 8
DEFINITION
Constructs: the building
blocks of programming.
.. Programming fundamentals
There are several constructs in programming and it is important to learn these so you can create
your own coding. All algorithms that are written for programming require some constructs in order
to work effectively.
... Sequencing
An algorithm contains instructions that are carried out one after another, and the sequence
determines the order that these instructions are carried out. For example, a basic algorithm for making
a cup of tea might look like this:
. Boil the kettle.
. Pour water into the mug.
. Stir.
. Put a teabag in a mug.
. Add sugar and milk.
. Drink the tea.
The numbers indicate the order of the steps, and these steps have been sequenced. Imagine if the
algorithm had been written like this:
. Put a teabag in a mug.
. Boil the kettle.
. Pour water into the mug.
. Stir.
. Add sugar and milk.
. Drink the tea.
REFLECT
Can you write an
algorithm for an everyday
procedure?
The Stir step is now in an incorrect place, and the drink would not taste as expected, however a
teabag could still be stirred at that point. This is a good example of a computer doing as it is told,
whereas humans would recognise that this sequence is wrong. It is therefore important that
programmers get the sequence of their programming right to produce the desired result.
... Selection
Another fundamental construct in programming is the ability for the code to make a decision or ask
a question, usually when there are several possible options.
Selection can be written into programs by using either an IF statement or a CASE statement.
Selection using IF statements allow a program to take different paths depending on the answer to a
question, and take the form of IF, THEN, ELSE instructions. For example, an algorithm could show a user
the most appropriate directions to a destination based on their mode of transport. The steps might be:
. Find out if you are in a car or on public transport.
. If driving a car, show a map using roads.
. Otherwise show a map with bus and train routes.
When preparing this algorithm for programming, we might consider the following:
. Are you driving a car or using public transport?
. IF you are driving a car, THEN look at this road map for directions.
. ELSE look at this map that contains bus and train routes.
Depending on the answer that is given at Step , the program can follow two different paths: one for
someone driving themselves, and another for someone using public transport.
Another form of selection is by using a CASE statement. This is where a set of options are
programmed for a question that has many different potential outcomes. For example, a program
may look up the answer to a question based on some similar variables, and output a word or phrase
based on the answer. Look at the following code from the Java programming language:
ENRICHMENT
Write an algorithm in
standard English that
contains an if, then,
else scenario.
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CASE clothing of:
Shirt: OUTPUT “Monday”
BREAK;
Jacket: OUTPUT “Tuesday”
BREAK;
Shoes: OUTPUT ‘Wednesday”
BREAK;
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Chapter 8
Jumper: OUTPUT “Thursday”
BREAK;
Shorts: OUTPUT “Friday”
BREAK;
DEFAULT: “I don’t know this clothing”
The selection will go directly to the appropriate line of code based on the input or condition that is
being tested, in this case an item of clothing that is associated with each day of the working week. If
the condition is not recognised, the program will go straight to the DEFAULT output.
... Iteration
Iteration takes place in an algorithm where the rules determine that a step or steps should be
repeated until a condition is met or until told to stop. Iteration is therefore the process of repeating
the steps in a program.
A straightforward algorithm for eating toast might be as follows:
Make the toast.
Put toast on the plate.
Put butter on the toast.
Cut toast in half.
Eat slice of toast.
Repeat step  until all of the toast is eaten.
Wash the plate.
By inserting the line ‘Repeat step  until all of the toast is eaten’ the program is able to be simplified
by giving a repeat command until a condition is met, in this case when the toast is eaten.
Another word for iteration in programming is loop. In effect, the program is looping Step  until the
set condition is met.
There are different types of loop in iterative programming.
Type of loop
HELPFUL NOTES
It is important to note
that the CASE structure is
not built into the Python
programming language.
HELPFUL NOTES
Iterating is the process of
repeating an instruction
as many times as the
program requires.
Description
Count-controlled loop The number of loops or iterations is already decided. A counter is used
to record how many times the iteration has occurred. This type of loop is
known as a FOR loop. (Example A)
Pre-condition loop
This is where a condition must be true before the loop or operation takes
place. This type of loop is known as a WHILE loop. (Example B)
Post-condition loop
This is where a condition must be true after a loop or operation has
taken place. In the C programming language, post-condition loops are
implemented using a DO-WHILE loop. (Example C)
Another type of post-condition loop is a REPEAT ... UNTIL loop. This
repeats what is within the loop until the condition defined at the end is
met. A pseudo-code example of this would be
count = 0
REFLECT
Can you write an
algorithm in standard
English for something
that requires repeat
actions?
REPEAT
count = count + 1
OUTPUT count
UNTIL count == 10
This will output a count from  to .
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Chapter 8
Worked Example
Example A: Count-controlled loop (FOR)
If a program was written to add three lives to a total number of lives, the Python code could
read like this:
ADD Life
ADD Life
ADD Life
More efficient code would be::
REPEAT (ADD Life) 3 times
We would therefore write the actual code like this:
FOR count IN range(1,4):
PRINT(“Add Lives: “ + str (count))
This code would repeat the add lives command three times.
Example B: Pre-condition loop (WHILE)
This is a loop carried out while a question or a condition is true or false. If a program was
written to check that a door was open before switching on a light, the algorithm might look
like this:
Is the door open?
QUICK CHECK
What are the three types
of iteration? Can you
confidently explain the
differences?
Give the light electricity while the door is open
A piece of Python code might look like this:
Light = INPUT(“Type shut when you go out: “)
WHILE Light!= “shut”:
PRINT (Light)
Light = INPUT(“Type shut when you go out: ”)
This code would keep on asking the user to confirm the door was shut in order to end the
pre-condition loop and would carry on checking while the program was iterating.
Example C – Post-condition loop (DO-WHILE)
This is a loop that would be carried out after a condition is checked for either a true or false
answer to a question. Therefore, a do-while loop would always run once, even if the condition
checked is false, and would stop after the single iteration. If the condition was true, the loop
would iterate again.
It is important to note that the DO-WHILE iteration is not built into the Python programming
language. Consider this algorithm:
Are there  litres of water in the bucket?
Turn the tap off when there are  litres of water.
A piece of code from the Java programming language might look like this:
LINK
WB
Consolidate your
understanding by
completing Exercise 5,
page 96 in the Workbook.
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SB CS PP.indb 116
COUNT = 1
DO
PRINT(count)
count+=1
WHILE count <5
This type of loop would repeat until the while line returned a false value. It would then stop
the program.
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Chapter 8
... Totalling and Counting
We now know that programs can use a counter when using a FOR loop. Counting keeps a check on
how many iterations a program has performed in a loop. For example, you might wish to count a
number of attempts at a level in a game. We might write a counter into Python code like this:
count = 0
WORD ALERT
count = count + 1
It is possible to insert the counter into an iterative loop to increment by  each time the loop is
carried out.
Increment: to increase
by a set number.
Totalling is used to add one number to an existing stored number, usually contained in two different
variables. For example, you might wish to add the number of different objects collected by a player
in a game. We might write a total in code like this:
total = total + items
Total and items are two different variables, and data would be stored in both.
REFLECT
... String Handling
Strings are a data type used to hold combinations of letters and numbers, or alphanumeric
characters. Strings are variables that can be assigned names and can be handled in several different
ways within programming.
Have you ever played a
game where a feature
included a counter?
A string might look like this in Python code:
Name = “Greg”
HELPFUL NOTES
The variable ‘name’ contains the combination of letters ‘Greg’. The contents could also include
numbers and symbols.
We are now going to look at the different ways strings can be handled.
Strings can contain letters,
numbers and symbols.
Length
Coding can be used to discover the length of a string by using the syntax LEN. For example:
LEN(Name)
This Python code would return the answer ‘g’, as this letter is in the third position of the string ‘Greg’.
Character position
Another feature of string handling is determining the content of a character position in a string. For
example, we may wish the coding to look up the character at position  in the string:
Name[3]
This Python code would return the answer ‘g’, as this letter is in the third position of the string ‘Greg’.
The reason ‘g’ is returned and not ‘e’ is because here the first character is in position []. However, in
some programming languages the first character of a string is denoted by position [].
Substring
WB
LINK
Consolidate your
understanding by
completing Exercise 7,
page 104 in the
Workbook.
Another form of string handling is asking a program to look up a substring, or a set of characters
from within a string.
Name = “Greg”
OUTPUT substring(1, 2, name)
This Python code routine would return the characters ‘re’ from this code. The routine instructs the
program to create a substring from the variable ‘name’, starting at character position  (‘r’) and ending
at character position  (‘e’).
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Chapter 8
Upper and lower
QUICK CHECK
Why does position [3] in
the example output the
letter ‘g’?
This form of string handling turns all the lowercase letters in a string into uppercase (upper) or all the
uppercase letters in a string into lowercase (lower), and then returns it. For example:
Name = “Greg”
Print(Name.UPPER())
This Python code would return the output of GREG, as the ‘reg’ part of the string has been converted
to uppercase.
Name = “Greg”
PRINT(name.LOWER())
ENRICHMENT
Can you think why it
would be useful to output
a portion of a string?
REFLECT
Many popular games
use this coding feature
to personalise a game.
A user is asked to enter
their name, and it then
appears throughout the
gameplay.
This Python code would return the output of greg, as the ‘G’ part of the string has been converted
to lowercase.
... Arithmetic, Logical and Boolean Operators
An important feature of programming is the ability to carry out mathematical operations. The tables
below show the different types of operations that can be carried out within programming languages
and some example syntax.
Arithmetic Operators
These operators are used to carry out arithmetic calculations.
Operator
Purpose
Syntax
+
Carrying out an addition
Lives = Lives + 1
−
Carrying out a subtraction
Lives = Lives - 1
*
Carrying out a multiplication
Lives = Lives * 2
HELPFUL NOTES
/
Carrying out a real division
Lives = Lives / 2
Many of these operations
are identical to
mathematics.
^
Raised to the power of
MOD
DIV
Lives = Lives^2
Finding a remainder from the
division of two numbers
Lives = Lives MOD 3
Carrying out an integer division
Lives = Lives DIV 3
The difference between a real division and an integer division is that an integer division can only be
carried out where the two pieces of data being divided are both integers. Where one of the pieces
of data is not an integer, and instead may be a floating-point piece of data, a real division should be
programmed instead.
Logical Operators
These operators are used to carry out comparisons and are often found in iterations.
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Chapter 8
Operator
Purpose
Syntax
=
Assigning a value to a variable (assignment)
Lives = 10
<
Less than
IF Lives < 10
<=
Less than or equal to
IF Lives <= 10
>
Greater than
IF Lives > 10
>=
Greater than or equal to
IF Lives >= 10
<>
Does not equal
IF Lives <> 10
Boolean Operators
These operators are used to help a program make more complex decisions.
Operator
Purpose
Syntax
LINK
If something and something else are true
or false
IF Lives > 5 AND
Health >=10
OR
If something or something else is true
or false
IF Lives > 5 OR
Health > 10
NOT
If something is NOT true or false
WHILE NOT Lives
AND
Chapter 10.
.. Nested Statements
We have already learned about the programming constructs of selection and iteration. Sometimes
it is necessary to execute one IF statement, followed by another, followed by another. This would
form a subroutine, whereby the results of the first selection would execute the inner selection, which
in turn would execute the innermost selection. The same would happen with an iterative process,
whereby the results of the first loop would execute the inner loop, which in turn would execute the
innermost loop.
We refer to this type of iteration as nesting, and both selection and iteration is capable of these
constructs.
Nested Selection
This type of programming usually involves several decision points within a process. For example, if
Film A was rated at , and Film B was rated at , some Python code could be written for making a
decision on whether someone could view one of the films.
Age = int(input(“What is your age? “)
IF Age >= 12 THEN
OUTPUT(“You are able to watch Film A”)
ELSE
IF Age >= 15 THEN
OUTPUT(“You are able to watch Film B”)
ELSE
OUTPUT(“You cannot watch any of the films”)
ENDIF
ENDIF
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Chapter 8
Nested Iteration
In the same way as a selection can be nested, a loop can be nested inside another loop. In this example,
the inner (nested) loop would output ‘ to ’ four times because of the iterations specified in the outer loop.
FOR Lives = 1 to 4
FOR Health = 1 to 5
PRINT(Health)
NEXT Health
NEXT Lives
You would need to be able to create nests of up to three levels of statements in your programming,
either as nested selection or nested iteration.
.. Procedures, Functions and Parameters
ENRICHMENT
Can you think of
a procedure or a
function that could be
used regularly? Hint:
think of formulaes in
mathematics.
Within a computer program there are different sections of coding that do different jobs. Some of
these sections are procedures, and others are functions. These can be run at set times within the
programming. Often, procedures and functions are run several times within a program, and so they
tend to be pre-stored within a programming language ready to be called when required. This saves
time as the programmer does not have to type out common functions and procedures repeatedly.
Programming languages come with functions and procedures that are pre-defined. However,
programmers will often write their own functions and procedures that are relevant to the program.
A function can be called by a procedure, but a procedure cannot be called by a function.
Worked Example
A procedure
If a program needs to create several equilateral triangles of the same size, the algorithm to
create one triangle might look something like this:
Repeat  times
Draw a line length 
QUICK CHECK
What is the difference
between a procedure and
a function?
Turn right  degrees
This procedure could then be named triangle and at any point the programmer could run or
‘call’ the triangle procedure to run this code.
A function
If a program was required to find the perimeter of a triangle, the Python code might look like this:
Perimeter_Triangle = (Line * 3)
RETURN Perimeter_Triangle
This function would be able to be used at any point to return a perimeter of a triangle where
the line length variable had been previously defined. This calculation would be stored as
Perimeter_Calculate, and this could then be returned and used in the program
whenever needed.
WORD ALERT
Function: a block of
organised, reusable code
used to perform a single,
related action.
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To carry out processes, a function or procedure sometimes requires additional information or
instructions from the programmer. These instructions are called parameters and are the names of
information required.
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Chapter 8
Our triangle procedure in the worked example had a preset line. This could easily be swapped for
a variable instead, which for example could be called Linelength. This parameter could then be
inserted into the procedure, and a line length could be added to the calling of the procedure instead
of the length being hard coded into the procedure. This makes for more efficient coding:
Triangle(100)
This line, with a parameter built into the triangle procedure, would then draw a triangle with sides
of length . The number is called the argument; procedures and functions can have multiple
arguments, separated by commas, as long as there are parameters built into the code that are
waiting to accept those arguments.
REFLECT
There are also differences in the variables that can be used by functions and procedures:
• A global variable is declared outside of functions and procedures and can be used within any
function or procedure in the program.
• A local variable is declared inside a function or procedure and can only be used by the function
or procedure that it is contained within.
.. Library Routines
Library routines are small blocks of pre-written code that are stored within the library (a type of
database) of a programming language. These are perfectly programmed routines that can be called
upon at any time with no pre-programming required and are designed to handle some of the most
common problems when writing any software.
Here are some common library routines:
What parameters might
you be able to attach to
a procedure that draws
a circle?
WB
LINK
Consolidate your
understanding by
completing Exercise 4,
page 95 in the Workbook.
• MOD: Short for modulo, this routine is used for finding a remainder from a division.
• DIV: Short for division, this routine is used for carrying out a division of two integers.
• ROUND: This function returns the output of the nearest integer to a floating-point number that is
passed to it.
• RANDOM: This function returns a randomly selected integer from a given range of integers.
.. A Maintainable Program
It is important for programmers to create tidy, well-explained and efficient code. It is highly likely that
at various points in the coding process the code that has been written will be passed on to another
programmer to work on, complete or test. If the coding is messy, inefficient or lacks sufficient
explanation, this can make the process of handing over very difficult or even impossible.
Meaningful Identifiers
It is very important that the variable names used within code are related to the data contained inside
that variable. For example, the variable name ‘item’ does not describe what that variable contains
or is used for. The same goes for constants, arrays and procedures – all identifiers should be easily
recognisable by programmers to ensure the code can be easily read.
Commenting
Adding commentary to lines of code is a feature in all programming environments. These are lines
of description that are added next to actual code. Comments are not executed by the program and
are separated from the coding using a special symbol. These symbols are different depending on the
language being used. Commentary can show what a programmer or developer was thinking at the
time of writing a particular line or set of lines of code, and any programmer working in a team would
be able to access other people’s coding much more easily.
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ENRICHMENT
Look for some other
common library routines
in the programming
language that you use.
HELPFUL NOTES
Line numbers in
programming are vital.
You can use them to
quickly identify errors
in coding.
REFLECT
Think about your own
programming. Would your
comments be able to be
understood by someone
who had no knowledge of
your program?
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Procedures and Functions
Many common procedures and functions that are stored in the library (see .. Library Routines)
have set names that are common across most high-level programming languages. When a
programmer is writing their own procedures and functions, it is important that the names they give
are not likely to cross over with anything else, as this would cause an error in the programming.
For example, if writing a procedure to draw a circle, the procedure could not be called Round
because this is already in use within the library. A better name would be Circle as this would not
ordinarily be used by another function or procedure.
LINK
WB
Consolidate your
understanding by
completing Exercise 8,
page 106 in the
Workbook.
. Arrays
In .. we learned that variables are memory locations that can store a piece of data. An array is a
series of these memory locations, where all of the data that is stored are related in some way – the
same data type. Each location can still only store one piece of data, but locations can be grouped
together. In Python, arrays are created using the LIST functionality.
Worked Example
A program may be required to store five colours. The code could be written like this:
Colour_0
Colour_1
Colour_2
Colour_3
Colour_4
While this would work for storing the five colours, an easier way to store the data is in an array:
Colour(4)
REFLECT
Imagine a table like this, called colours:
What is the difference
between a one- and
two-dimensional array?
Colours





Red
Green
Blue
Purple
Orange
The number in brackets defines the index and determines how many pieces of data can be
stored in the array – in this example, the number  would allow five items to be stored. As we
learned in Section ..., computers begin counting at the number , however some languages
do begin counting at number .
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Arrays can be both one- and two-dimensional. The colours example above is a one-dimensional
array: one row and multiple columns. A two-dimensional array has multiple columns and multiple
rows of data, all with the same data type – this looks a bit like a grid. One example of a twodimensional array is where a program needs to map out a game world of a fixed size, with each
square of the game world containing data to define the type of land in a square.
World [20][20]
The code above would allow a programmer to define a flat world in a game that is  squares wide
by  squares in length using a two-dimensional array. More complicated game environments use
three-dimensional arrays.
ENRICHMENT
Think of a game where
the world appears to be
three-dimensional. Try to
imagine the size of array
that exists to code just
the world without any
characters in it.
Data can be read from and written into arrays depending on the functionality of the programming.
If the program was required to read the third value from the colours array in our example above, the
following code could be used:
Colours[2]
This would give an output of Blue, the third colour in the array.
It is also possible to change or write to an array, for example in the code below, which would change
the data in array position  from green to pink.
Colours[1]=”Pink”
It is also possible to create, write to and read from arrays using iteration. Creating an array using this
method could be done using a nested FOR loop:
World= [[0 FOR x IN range (5)] FOR y IN range (5)]
This code would create a two-dimensional  ×  array.
REFLECT
Can you think of a
scenario in a game where
data in an array might
need to be changed by
a program?
The array could then have data written into each position, which is similar to grid references on
a map:
World[0][0] = ‘Red’
World[0][1] = ‘Blue’
World[0][2] = ‘Orange’
World[0][3] = ‘Orange’
World[1][0] = ‘Green’
[0]
[1]
[2]
[3]
[0]
Red
Blue
Orange
Orange
[1]
Green
[4]
WB
Consolidate your
understanding by
completing Exercises 1
and 2, pages 107-110 in
the Workbook.
[2]
[3]
[4]
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LINK
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Chapter 8
. File Handling
HELPFUL NOTES
Files that are handled by
programming languages
tend to be text files, such
as those viewable in a
program like Notepad.
We have seen that programming involves the input of a lot of data, whether as variables and
constants or output of results of operations. It is therefore often important to store program data
in external files so that it is not lost when a program has finished running. Programming can often
take weeks and months to create, and to be constantly restoring data to code would be hugely
time-consuming.
To enable greater efficiency, programming languages have the ability to handle external files of data.
The files can be both read from and written to. When reading from a file, a program can be instructed
to open it, read from it and close it again. When writing to a file, a program can be instructed to open
it, write data to it, save it and close it.
.. Reading from a File
When reading from a file, a program will read records one line at a time. Data held in a file can be
read into a variable or into an array.
Here is an example of Python code for reading a single line from a file called colours.txt that
has only got one line of information:
FILE = openRead(“colours.txt”)
Colour = myFile.readLine()
FILE.CLOSE()
This Python code would open the colours.txt file, read the contents of the file into a variable,
create a single record from this data and then close the file. If a file has multiple lines of data, this
would have to be read into an array and would create multiple records.
.. Writing to a File
A program can also be set up to write the contents of a variable or an array to a file – the reverse
of the reading operation. Data is written into a file one line at a time. An example of this is shown in
the Python code below, where the contents of the colours array can be stored in a file called
colours.txt.
LINK
WB
Consolidate your
understanding by
completing Exercise 1,
page 111 in the
Workbook.
FILE = openWrite(“colours.txt”)
FOR x = 0 TO 5
file.writeLine(colours[x])
next x
FILE.CLOSE()
This Python code would write the data stored in the colours array to the colours.txt file line
by line.
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Chapter 8
Let’s Map It
Sequence
Logical order
Selection
Constants
If something is true THEN
do this ELSE do that
Don’t change
Iteration
Variables
Looping until
something happens
Can be changed
INPUT
PROGRAMMING
OUTPUT
Procedures and
Functions
Data types
Integer
0, 1, 2, 3
Real
1.3, 2.6, 3.7
Char
£, $, ¥
String
hello
Boolean
True/False
Pre-named and
Pre-defined
LIBRARY
Files
Arithmetic
Arrays
+ - * / = ><
Tables of data
Boolean
AND OR NOT
Read from
Write to
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Chapter 8
Let’s Review
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
What is a variable?
Name two data types used in programming.
Explain what the programming construct of sequence means.
CASE statements are one form of selection – name another.
Name the three types of iteration loops.
What is the purpose of counting in programming?
When handling strings, name two ways in which they can be changed.
Addition and multiplication are two arithmetic operators. Give another three.
What is the meaning of the logical operator <>?
Boolean operators are used for complex decisions. Explain the three common operators, AND,
OR, NOT.
What does it mean to use a nested statement?
What is a parameter?
What is the difference between a local and a global variable?
Name two library routines in a programming language.
Why is it important to use meaningful names to identify variables and constants?
What is the commenting feature of a programming environment?
What type of item is stored in an array?
True or false: data can only be read from an array.
Why do programming languages use external files for data storage?
True or false: a program reads all of the lines from a file in one go.
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CHAPTER
9
Databases
COMPUTER SCIENCE WATCH
Scan the page to watch a clip on database
management systems.
Before watching discuss what you expect to
see or hear.
QUESTIONS
At the end of this chapter, you will be able to:
understand what is meant by a database, including features such as tables,
fields and records
• How are records maintained in
organisations like your school or any
other place?
• Ask your elders and understand the
different methods of record keeping in
earlier times.
be able to suggest suitable basic data types for fields
identify the purpose of a primary key in a database
understand structured query language (SQL) and how to use it to
create queries
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Chapter 9
QUICK CHECK
What is the difference
between data and
information?
. Understanding Databases
Let us first understand what data is. Data can be
anything that can be stored on a computer, like
numbers, letters, characters, images and so on.
Have you seen the computer-generated bills from a
supermarket, or a shop (Figure .)? What information
do you get from the bill? Had there been no mention
about the item ID or name, would it be easy to
understand the purchases made? When the data
is presented in a meaningful way, what you get is
information.
A database is an organised collection of data. In a
database, you can organise data in a table format.
It also allows the user to work on data in the
following ways (Figure .).
Ad or remove
data
HELPFUL NOTES
Microsoft Access is one
of the most popular tools
for working on databases.
Since it comes along
with the Microsoft Office
Suite, the interface is very
similar to other Microsoft
applications.
Figure . A sample shopping bill.
Database
Manipulate or
change data
Access or
analyse data
Avoid data
duplication
Maintain data
accuracy and
consistency
Share data
Store data
Figure . Uses of a database.
REFLECT
Can you think of more
places where a large
amount of data is stored
using a database?
Databases are used in different places to store and manage information about almost everything.
Some common applications of databases are:
Student and examination records at schools and universities
Book records at libraries or book stores
Patient records at hospitals (Figure .)
Customer records at banks
ENRICHMENT
Find out how a country’s
population data is stored.
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Booking and reservation records at railways and airports
Employee records at offices
Online registration records for websites and social media
Figure . Accessing medical records.
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Chapter 9
.. Important Terms related to Databases
Table: In a database, data is entered in a tabular format, that is, organised as rows and columns to
provide meaningful information. This structured entry of data helps the user to access and manage
the information easily.
A column in a database table is referred to as a field. A field is like a title given to every single piece
of data. Each row is called a record, which is a collection of fields in the table for a specific person,
item or any other entity.
Let us look at an example of a database table showing records of students appearing for their final
examination. Here the field names are given by Student ID, First Name, Second Name, Date of Birth,
Contact number.
A column or a field
WORD ALERT
Entity: object or thing.
QUICK CHECK
What is a field?
A row or
a record
Figure . Student record table.
Query: Sometimes you need to work with a very large database. In such cases, it may be difficult
to find specific data required by the user. A query allows the user to find full records or records with
specific fields in a database using certain criteria. For example, in the student record database
(Figure .), you can run a query to find the information of students from roll numbers  to . You will
learn more about how to use a query for practical purposes later in this chapter.
WORD ALERT
Criteria: conditions or
questions.
Data types: A field in a database table can have its own attribute or property. For example, you
can enter data as text, number, date/time, currency and so on. These attributes are defined as data
types. A data type helps the computer to identify similar data for the purpose of sorting, searching
and calculation. Mostly data types may be defined differently in various database systems. Some
common data types are as given in Table ..
Table . Some common data types.
Data type
Text/Alphanumeric
Character/Char
Integer
Number/Numeric
Real
Attribute description
Example of field name
Sample data
Used for data which
is text or number or a
combination of both.
Student name, phone
number, address
David,
Used for defining data
with a fixed-length string
that may contain letters,
numbers and/or special
characters.
Name, address, title
Mr,
Used for data which is a
whole number.
Roll number, ID, number
of items
Manisha
WORD ALERT
String: a set of characters
that can also contain
spaces and numbers.
Mrs,
Miss
,

Used for numbers greater Height, weight, score
than zero and may require
calculations. It can also
have a value in decimals
or percentages.
.,
Used for data in a
computer program which
are decimal numbers.
., .
Weight, height,
temperature
.,
.%
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Chapter 9
Data type
Attribute description
Example of field name
Sample data
Date/Time
Used for date or time.
Different formats of
date such as DD/MM/
YY and time such as
hours:minutes:seconds
can be selected.
Schedule, last date, first
date, time of action
//,
Used for data that include
currencies of different
regions around the world.
Item price, cost, tax paid,
amount credited
£.,
AutoNumber
Used for data which
can include randomly
generated numbers when
a record is added. This
field cannot be changed.
Registration number,
product ID, student roll
number


Boolean
Used for data which has a
value of / such as True/
False, Yes/No, On/Off.
Answer (true/false), active
(yes/no), display (on/off )
Yes,
Currency
::
$.
no,
true,
false
DEFINITION
Primary key: A primary
key is a unique field that
allows the user to identify
a record.
Foreign key: A foreign key
is a field or combination
of fields that are related
to the primary key of
another table.
. Types of Databases
You can use different software applications like Microsoft Access, Oracle, MySQL, LibreOffice Base
to create a database. These applications are also called Database Management System (DBMS)
applications as they act as an interface between the user and the database. A database can be of
two types — Flat-file (single-table) database and Relational Database (Table .). Different
DBMS applications work on any one type or both types of database according to how they are
programmed. For example, Microsoft Access can work on both flat-file and relational databases.
Thus, Access is also a Relational Database Management System (RDBMS).
Table . Types of databases.
HELPFUL NOTES
A primary key cannot
have a duplicate value
in a database. Also, this
field cannot be left blank.
WORD ALERT
Data duplication: a
process of creating an
exact copy of data.
Data redundacy: the
storing of the same data
in multiple locations.
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. Flat-File Database (singletable database)
A flat-file database stores
simple data formats. They store
only a single table of data. The
information given by a record is
complete with a fixed number
of fields. This database is not
related to any other table or
database. An example is shown
in Figure .a.
This method of storing data is
not efficient and may lead to
problems like data duplication,
data redundacy and input errors.
. Relational database
When a database can have mutiple related tables, it is referred to as
a relational database. When the tables are linked, the user can work
on complex data structures having multiple tables (Figure .b).
For example, in a student database, you can create a Student
Information table and a Student Examination table.
In the Student Information table, Student ID will be unique for
each student record. It thus defines the record of each student. This
special field is defined as the Primary key for that table. Now, when
you link the Student Information table and Student Examination
table, the two tables can have a common field, that is Student IDs.
A relational database does not allow data duplication. Also, it is
more effiecient and consistent than a flat-file database.
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Chapter 9
WB
(a) Flat-file or single-table database
Consolidate your
understanding by
completing Exercise 1,
page 115 in the
Workbook.
(b) Relational database
Figure . Example of databases.
Activity
1
2
LINK
An organisation keeps a record of its employees in separate tables like Employee Joining Details,
Employee Payroll Record, etc. Suggest a common link which can help to retrieve all the records
of a particular employee. Which type of database must be created?
Fill in the blanks.
a) A database is an organised collection of __________.
b) A flat-file database is also referred to as __________.
c) A ________ key is a unique field that allows the user to identify a record.
d) The full form of DBMS is __________________________________.
. Creating a Database
.. Creating a New Database with the Given
Information
Let us look at the given information.
In an inter-school annual sports meet, registration forms were collected with the following
information. You are asked to enter the information from the forms into the student database.
Given below is the information collected from different schools.
•
•
•
•
•
•
•
•
Registration Number
School Name
Student ID
Student Name
Age
Gender
Contact
Sport Selected
HELPFUL NOTES
If the application is open
then you can create a new
file using the File tab in the
open document.
You can create a table using any database application. Here, you will be looking at Access .
To create a database in Access, follow these steps.
Step 1: Open the Access  application.  Step 2. In the Backstage view click on the Blank
database option (Figure .).  Step 3. A dialogue box opens (Figure .)  Type the name of the
database as Annual Sports Meet.  Step 4. Click Create.  Access  window will open.
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SB CS PP.indb 131
To create a new database
file, you can either select
the Blank database option
or a built-in template.
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Figure . Backstage view of Access 2016.
Figure . Creating a new database file.
.. Creating a Table
Access has two views to work with data: Design View and Datasheet View. These two views can
be toggled with the help of the View option under Home tab (Figure .).
Figure . View option.
Although both the views allow the user to create and define the table structure, the Design View is
easier to work with.
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When you switch to the Design View, you will be prompted to save the table. Enter the table name
as Student Participation Table and click OK (Figure .).
Figure . Saving a table.
The Access window will show the Design View. Now, you can add the Field names for a record,
define its data-type and mention the Field Properties. You can also set the Validation Rules from
the Properties pane (Figure .).
Figure . Entering table fields and defining data types in Design View.
By default, the first field is marked as a primary key (shown by a key icon). You can change the
primary key by right-clicking on the desired Field name and selecting the Primary key option or
just select the Field and click on the Primary key option under the Design tab.
.. Data Validation
You have learned that data can be a name, date of birth, address, currency, date/time, and so on.
There are certain rules that are followed when data is typed into a database system called the data
validation rules. For example, a phone number does not contain a character or an alphabet. These
rules help in accepting the data which are as per the set format.
The data entered into a database can sometimes be entered incorrectly. It can be invalid,
inconsistent or incomplete. To avoid any such issue, the user may apply different validation checks.
Some of these are given in Table ..
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DEFINITION
Data validation rules: these
are some rules which help
the user to know that the
data being entered in a
database is correct.
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Table . Types of data validation checks.
Validation
technique
Purpose
Example
Presence check
To check the missing data in the
field. The system does not move
further if this data is not filled.
A primary key in a database is
mandatory.
Range check
To check if data is within the set
range.
Days of a week must be between 
and .
Length check
To check the desired length of data
characters is met or not.
If the format of time is hrs:min:sec,
the system will require  digits to be
entered, anything less than  digits
will not be considered valid.
Format check
To check if data is in the desired
format.
The date format followed in a form
can be mm/dd/yyyy.
Consistency check
To check that data is consistent as
per any previous entry.
The date of expiry of an item cannot
be before the manufacturing date.
Type check
To check the data type.
A phone number field cannot allow
characters.
You can add a validation rule to a field using the Field Properties Pane (Figure .). Once the data is
entered, a validation check can also be performed. To do so, select the Design View  Design tab 
Click on Test Validation Rules.
Figure . Creating validation rule for Student Participation Table.
.. Entering Data in a Table
When a form is designed, save the table and switch to the Datasheet view to enter the data values
(Figure .).
Figure . Annual sports meet database.
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. Using Queries
HELPFUL NOTES
Queries are used for working with data in a database. You can search data by certain criteria such as
“searching the records in which the students have participated before”. You will get the matching
records in the database.
You can create queries
by choosing one or more
search criteria.
Structured Query Language (SQL) is mainly used for creating and running a query in order to
search, sort or manipulate data.
However, some DBMS systems like Access also allow the user to create a query using a Graphical
User Interface (GUI). This is sometimes referred to as query-by-example.
.. Using Query-by-Example
WB
Using the Student Participation Table created earlier, let us create and run a query to search the
records of all students playing the sport ‘Baseball’.
To do so, follow the steps given.
Step 1. Open the database - Annual Sports Meet.  Step 2. Click on Create tab  Query
Design option.  Step 3. A new tab opens in the Access window called Query 1. 
Step 4. Select the table name from the pop-up window and click on Add. Click Close to close the
pop-up window.  Step 5. A list of all fields in the table appears in the top pane of the Query 1
window. You can create a query and set a criterion or multiple criteria to search the database by
filling up the options in the lower pane of the Query 1 window (Figure .).  Step 6. Run the
query by clicking on the Run option
in the Design tab. The required data will appear (Figure .).
LINK
Consolidate your
understanding by
completing Exercise 2,
page 116 in the
Workbook.
Figure . Creating a query.
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Chapter 9
Figure . Results of a query.
.. Using SQL Programming
SQL is mainly used for relational databases. It contains statements which are used to retrieve or
modify data from the database.
Access also allows you to use SQL to create queries. Let us again take the example of the Annual
sports meet database.
To create a query using SQL, follow the given steps.
Step 1. Open the Query 1 tab  Once this tab is opened you will notice one more view in the
View tab called SQL view (Figure .). Select the SQL view. The Query 1 window will change to
the programming environment for SQL.  Step 2. Type the SQL queries and Select Run from the
Design tab.
Creating the SQL query to retrieve data from the
database
The syntax used for Data Query Language is:
SELECT [Field Name] FROM [Table Name];
Now, let us understand the application using Student
Participation Table.
. Using * for the field name
This will retrieve all properties (fields) of a table
Example
SELECT *
FROM [Student Participation Table];
Figure . View tab with SQL View option.
HELPFUL NOTES
Some more operators you
can use with WHERE clause
< Less than
> Greater than
= Equal to
!= Not equal to
<= Less than and
equal to
>= Greater than and
equal to
BETWEEN Within a defined
range of data
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Figure . Output for SQL query using.
Output: You will get the complete table information
including all Field names.
. Using WHERE clause
WHERE clause is added to specify a condition. When
this clause is added to a SQL query you will get only
those records for which the condition is true.
Example
Figure . Output for SQL query using
WHERE clause.
SELECT [Registration Number], [Student ID], [Student First Name]
FROM [Student Participation Table]
WHERE Age<=;
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. Using ORDER BY clause
ORDER BY clause is used along with the
SELECT statement to retrieve information
in ascending order. In case you require
information to be arranged in descending
order, DESC is used along with the ORDER BY
clause.
Syntax
For Ascending order (Output Figure .)
SELECT [Registration Number], [Student ID],
[Age]
FROM [Student Participation Table]
ORDER BY Age;
Figure . Output for ORDER BY ascending order.
For descending order (Output Figure .)
SELECT [Registration Number], [Student ID],
[Age]
FROM [Student Participation Table]
ORDER BY Age DESC;
You will also learn about two more functions,
COUNT and SUM. These are aggregate functions
which are used for performing mathematical
operations – counting and addition,
respectively on the data values of a given field.
COUNT function – It is used for counting the
number of rows in a field. You can add a
condition using WHERE clause.
Figure . Output for ORDER BY in descending order.
Example
SELECT COUNT (Age)
FROM [Student Participation Table]
WHERE Age = ; Output is shown in Figure ..
SUM function – It is used for adding the values in
a given field.
Figure . Output using COUNT
function.
You can use the SUM function to add the values
in the field, Reg_Amount (Figure .) using the
SQL query.
Figure . Reg_Amount field of Student Participation Table.
SELECT SUM (Reg_Amount)
FROM [Student Participation Table]; Output is
shown in Figure ..
Figure . Output using SUM function.
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Chapter 9
Activity
Answer the following.
 Name any DBMS application that allows creating a query using Query-by-example and
SQL, or both.
 The full form of SQL is _________.
 Which SQL function allows you to arrange data in ascending order?
 Write the syntax for a WHERE clause.
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Let’s Map It
Applications of a database
• Storing/sharing data
• Accessing data
• Manipulating data
• Adding/Removing data
• Avoiding data duplications
• Maintaining data accuracy/
consistency
Understanding databases
• Important terms related to databases
• Table
• Query
• Field
• Record
• Data types
• Primary key
Datatypes
• Text/Alphanumeric
• Character/Char
• Integer
• Numeric
• Real
Types of databases
• Flat-file database
• Relational database
• Date/Time
• Currency
• Autonumber
• Boolean
DATABASES
Creating a database
• Creating a new database
with the given information
• Creating a table
• Data validation
• Entering data in a table
SQL commands:
• SELECT
Using queries
• Using Query-by-example
• Using SQL programming
• FROM
• WHERE
• ORDER BY
• SUM
• COUNT
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Let’s Review







Define a database.
Explain the difference between flat-file and relational database.
Name some statements that can be used to retrieve data using SQL queries.
Define data types. State three data types.
Assuming you need to plan a health camp for your school, create a sample student database
assuming students between age group – will participate.
Explain validation. Why is it required? Give the names of any two types of validation checks.
In a hospital a patient database is to be created with the given fields
Patient First
ID
Name

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Second Contact Blood Date of
Name
Details Group Birth
Age
Doctor
Consulted
Date of
Visit
Fee
Paid
Assuming you have to maintain the patient database, create a database with at least ten records
and define the following.
a) Primary key
b) Data type for each field
In the above table create SQL queries for:
a) Selecting the patients who consulted a specific doctor
b) Getting a total sum of fee paid
c) Arranging the records in ascending order of Age
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CHAPTER
10
Logic Gates
and Circuits
QUESTIONS
• How could logic gates be used in everyday
life?
At the end of this chapter, you will be able to:
understand the different symbols that are used for logic gates
understand the function of a range of different logic gates
• How are logic gates and micro controllers
used in all computer systems such as
games consoles?
• What are digital circuits in computer
systems and how do they use binary values
1s and 0s?
use logic gates to create a logic circuit
complete a truth table
write a logic expression
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DEFINITION
Logic gates: the basic
units of a digit circuit
that control the flow of
electronic signals.
. Logic Gates
Logic gates are the basic building units of any digital circuit. Today, these circuits are used in almost
every computer system. From elevators to washing machines, logic gates are used all around you.
Digital circuit used to open electronic door.
WORD ALERT
This chapter will explore the types and functions of common logic gates.
Combination: a joining
of different parts or
qualities.
There are a number of different types of logic gate, with different logic rules. The combination
of several logic gates forms a circuit, which allows for the design and performance in modern
computers. The gates receive binary data, apply a Boolean operation and then output a binary result.
Arithmetic: use of
numbers to calculate an
outcome.
Boolean Operations
Equivalent: the same or
equal meaning.
HELPFUL NOTES
Be careful not to confuse
the Boolean operator ‘+’
with ‘+’ , which means
‘plus’ in normal maths.
The word ‘Boolean’ comes from Boolean algebra, which is the basis of computer arithmetic and
especially logic gates. There are only two Boolean values: true and false. They have equivalents in
normal language and in binary notation.
Boolean expressions can compare data of any type as long as both parts of the expression have the
same data. In computer science, Boolean expressions can be used in programming and produce
Boolean values when evaluated. Boolean values are either true or false:
Boolean value
Binary value
Synonyms
True

On
Yes
Positive
False

Off
No
Negative
There are also three logical operators: NOT, AND and OR. The Boolean operators for these are AND ‘•’,
OR ‘+’, and NOT ‘ ’, which is written above the letter.
Ā means NOT A.
A • B means A AND B.
A + B means A OR B.
Logic gates use both Boolean values and operators.
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Worked Example
We use Boolean logic all the time. Look at this situation using Boolean operators:
You have decided that you will do extra study if you are falling behind at school. You also decide
that you will do extra study even when you are not behind if your friend asks you to study
together. Express this using Boolean operators.
Solution
To express this formally and logically we need two pieces of information to make our decision
and another piece to represent the result of the decision. We can name our information like this:
WORD ALERT
Formally: officially /
explicitly.
Information needed to make decision
(behind at school) = TRUE if fall behind. If not, FALSE.
(friend asks you to study) = TRUE if friend asks you to study. If not, FALSE.
Result
(do extra study) = TRUE if we decide to do extra study. If not, FALSE.
Our logical expression is then:
(do extra study) = (behind at school) OR (NOT (behind at school)) AND (friend asks you to study)
This expression uses the three Boolean operators: NOT, AND, OR.
Activity
1
2
Write a logical expression like the example above for this given scenario.
There are two methods of getting to your part time job on time. You can get the bus but only if
you wake up before .am. If you wake up after this time, you will need to ask your parents to
take you in the car. If you wake up before .am but your parents offer to take you, then you will
always say yes as it is easier.
Draw the Boolean algebra symbols for the following:
a) A NOT B
b) A AND B
c) A OR B
HELPFUL NOTES
Types of Logic Gate
There are three basic types of logic gate that will be examined in this chapter: NOT, AND and OR.
NOT
AND
OR
WORD ALERT
The left side of the logic gate is referred to as the input and the right side as the output.
We can use a truth table to show the function of the logic gate. Each of the logic gates has a different
truth table. These truth tables display all possible input combinations and the correct output.
Logic Gates and Circuits
SB CS PP.indb 143
In all logic gates except
the NOT gate, there are
two inputs. The inputs or
outputs have two possible
states: a value of 1 or a
value of 0.
Referred: denoted /
identified.
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NOT Gate
A
DEFINITION
Truth tables: used to
represent the Boolean
expression of a logic gate
or logic circuit.
X
The NOT gate takes a single input, A in the diagram above, and always produces the opposite of that
input in a single output, X.
Here is the truth table for the NOT gate above. It displays all possible combinations of inputs and the
corresponding outputs for the NOT gate. There are only two possible outputs for a NOT gate:  and .
Input
Output
A
X




Besides constructing truth tables, we can describe each gate using logic notation and
Boolean algebra. In this case the output is as follows:
Logic notation: X = NOT A
Boolean algebra: X = Ā
ENRICHMENT
The total number of
possible combinations
can be obtained from
the formula C = 2n, where
C is the number of total
possible combinations
and n is the number
of inputs.
AND Gate
A
X
B
The AND gate takes the inputs A and B and produces the output, X. If both inputs are , then the
output will be , but otherwise the output will be .
Here is the truth table for the AND gate above.
For example, if there
are three inputs, A, B
and C, the total possible
combination of inputs is
C = 23 = 8.
Inputs
Output
A
B
X












Logic notation: X = A AND B
Boolean algebra: X = A·B
A and B show all possible combinations of inputs, so there are a total of four possible output states.
OR Gate
A
B
X
The OR gate takes two inputs, A and B, and produces output X. If either or both inputs is , the
output will be .
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Chapter 10
Here is the truth table for the OR gate above:
Inputs
A




REFLECT
Output
B




If someone asks you, ‘Do
you want a soda or some
water?’, you can’t answer
‘Both, please’. If you could
have both that would be
an inclusive use of OR. Is
the OR gate inclusive or
exclusive?
X




Logic notation: X = A OR B
Boolean algebra: X = A + B
Out of the four possible output states, the only time output X will be  is when both the inputs
A and B are .
An inclusive OR is what is shown in the truth table if either A or B is True, or if both are True, then the
statement value is True.
An exclusive OR only returns True when A OR B is True only.
Worked Example
A security light outside a house comes on after .pm or if it is dark. Make a table showing
the operation in normal language with corresponding Boolean and binary values. Make the
resulting truth table and choose the logic gate that will make this happen.
Solution
We have to state the conditions under which the light will come on:
if it is after .pm
if it is dark
WORD ALERT
Condition: the state of
something in relation to
its appearance, quality or
working order.
Then we convert these into the Boolean values ‘True’ and ‘False’:
it is after .pm = Yes/True/Positive
if it is dark = Yes/True/Positive
QUICK CHECK
Next we add the binary values:
it is after .pm
it is dark
Yes
Yes
True
True
Positive
Positive


In all logic gates except
the NOT gate, there are
two inputs. The inputs or
outputs have two possible
states. What are they?
Logic Gates and Circuits
145
Then we make the truth table. The inputs are ‘it is after .pm and ‘it is dark’:
Inputs
it is after .pm
it is dark
The light coming on is the output:
Inputs
it is after .pm
Output
it is dark
the light comes on
Remember that the light will come on if either of the conditions is true:
Inputs
it is after .pm
No
No
Yes
Yes
SB CS PP.indb 145
Output
it is dark
No
Yes
No
Yes
the light comes on
No
Yes
Yes
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Chapter 10
Finally, we can replace the normal language with binary and the inputs and output with letters:
Inputs
Output
A
B
X












This is the truth table for the OR gate.
Activity
1
2
Now do the same for these situations. You can skip some steps if you don't need them.
• To save electricity and be ecological, an ‘up’ escalator will start moving when a pedestrian
steps near the bottom and breaks a sensor beam. Tip: there is only one input.
• A car park barrier will rise when a car approaches and the driver puts the ticket they have paid
for in a slot.
Name the logic gates represented by these truth tables:
a
Input
Output
A
X




b
QUICK CHECK
Write the Boolean algebra
expression for NOT, AND,
OR gates.
HELPFUL NOTES
These three additional
logic gates look very
similar to 'AND', 'OR', 'NOT'
with some slight changes.
Knowing the appearance
of the basic gates will
make remembering them
easier.
Inputs
Output
A
B
X












c
Inputs
Output
A
B
X












Additional Logic Gates
In addition to the three logic gates shown above, there are also different versions of them: NAND, NOR
and XOR.
NAND
NOR
XOR
Figure . NAND, NOR and XOR logic gate symbols
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Chapter 10
The NAND Logic Gate
A
X
B
You can see that the NAND gate has a small circle after an AND gate symbol. This means that it is like an
AND gate plus a NOT gate. The NAND gate functions like an AND gate but with the opposite output.
The NAND gate takes the input A and B and gives output, X. It will only give an output of  if both
inputs A and B are .
Here is the truth table for the NAND gate above:
Inputs
Output
A
B
X












Logic notation: X = A NAND B
Boolean algebra: X = A·B
This means that the output X is always , unless both inputs A and B are  and then the output X is .
The NOR Logic Gate
A
X
B
Like the NAND gate, you can see that the NOR gate has a small circle after an OR gate symbol.
This means that it is like an OR gate plus a NOT gate.
The NOR gate takes the input A and B and produces an output of  if both inputs A and B are .
Here is the truth table for the NOR gate above.
Inputs
Output
A
B
X












Logic notation: X = A NOR B
Boolean algebra: X = A+B
The output X is always , unless both inputs A and B are  and then the output X is .
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Chapter 10
The XOR Gate
A
X
B
The XOR gate (which means ‘exclusive OR gate’) is similar to the OR gate, except that if both inputs
are  then the output is . The XOR gate has a different logic outcome to the OR gate: the output X is
 when either (but not both) of the A or B inputs is .
Here is the truth table for the XOR gate above:
HELPFUL NOTES
In Boolean algebra, the
symbol for ‘exclusive OR’ is
a ‘+’ inside a circle:
ENRICHMENT
You have now looked at
six logic gates. There are
actually seven – can you
find the other one?
Inputs
Output
A
B
X












Logic notation: X = A XOR B
Boolean algebra: X = A B or X = (A·B)+(A·B)
This also means that the output is  when both inputs A and B are  or .
Worked Example
Two people are walking towards each other along a corridor wide enough for two people to
pass. On one side of the corridor there are windows and on the other there is a blank wall.
Find the gate that describes the conditions where they can pass without bumping into
each other.
QUICK CHECK
Draw the logic gates for
NAND, NOR, XOR.
Solution
The inputs are:
Person  = A
Person  = B
And the values are:
Near the window = True
Not near the windows (near the wall) = False
Result
If both walk near the wall obviously, they can’t pass.
If A walks near the window and B near the blank wall, they can pass.
If B walks near the window and A near the blank wall, they can pass.
If both walk near the windows, they can’t pass.
REFLECT
What would happen if we
used an inclusive OR gate
to describe this situation?
Why do we need different
symbols for inclusive and
exclusive OR?
The truth table looks like this:
Inputs
A




Output
B




X




This is the table for the XOR gate. The XOR gate is an exclusive OR gate. If both inputs are true
then the output is false.
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Chapter 10
Activity
1
2
Now do the same for this situation. You can skip some steps if you don’t need them.
Tip: the circuits are normally on so something needs to happen if they go off.
• An alarm makes no warning sound if the door is closed and the window is closed. There are
hidden switches on the door and window through which a current is constantly passing. If
someone opens the door or window, the alarm sounds.
Name the logic gates represented by these truth tables:
Inputs
a
B



X






Inputs
WB
Output
A



B



X






LINK
Consolidate your
understanding by
completing the Exercises
1-2 from pages 123-129
in the Workbook.
Logic Gates and Circuits
SB CS PP.indb 149
Write the Boolean algebra
expression for NAND,
NOR, XOR.
Output
A



b
QUICK CHECK
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Chapter 10
. Combining Logic Gates
WORD ALERT
Complex: more difficult
/ more components
involved.
Basic logic gates can be combined together in a certain way to get different outputs. These allow for
complex operations to be carried out, for example, controlling a processing unit.
The combination of two or more logic gates forms a logic circuit.
Just as individual gates have truth tables, logic circuits have their own, more complex, truth tables.
Logic Circuits
Worked Example
REFLECT
Examine the truth table for this logic circuit, below.
Create your own logic
circuits using the AND, OR
and NOT gates.
B
P
X
A
Draw the corresponding
truth tables.
Input
A




Intermediate output
Output
P = A AND B




X = NOT (A AND B)




B




Solution
A
P
X
B
HELPFUL NOTES
When combining logic
circuits it is often easier
to break them down into
smaller sections.
Part 
Part 
We can see that Part  of the circuit is an AND gate. The intermediate output is at P. Part  of the
circuit is a NOT gate, and therefore X = NOT P.
The truth table can then be constructed as follows:
Input
LINK
WB
Consolidate your
understanding by
completing Exercise 2 in
the Workbook, page 127.
A




B




Intermediate output
Output
P = A AND B




X = NOT P




If we look at only the initial inputs A and B and the final output X, the truth table becomes:
Inputs
A




Output
B




X




This is also known as a NAND gate, which was discussed above.
150
SB CS PP.indb 150
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14.5.21. 14:16
Chapter 10
Activity
ENRICHMENT
Make this logic circuit into a table that shows the intermediate outputs and the final outputs and
that has the same function as the NOR gate.
A
B
Gate?
P
Create revision cards on
the rules for each of the
six logic gates we have
discussed.
X
Part 
Part 
Inputs
Intermediate output
Output
A
B
P
X


?



?



?



?

Logic Circuits with More Than Two Inputs
A logic circuit with three inputs is known as a two-level logic circuit.
The more inputs in the logic circuits, the more possible combinations there are. For example, if there
are three inputs and each one can take two values ( or ), then  ×  ×  =  rows will be required.
A
P
B
X
Q
C
REFLECT
Do you think it is cheaper
to use simple logic
circuits like this AND
gate and NOT gate or to
find a single gate that
will perform the same
function, such as a NAND
gate?
Break down the logic circuit into sections.
1 Work out P by completing the OR gate:
P = A OR B
This can then be added to the P column in the truth table below.
A
P
B
Logic Gates and Circuits
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Chapter 10
2 Work out Q by completing the NOT gate.
Q = NOT C
HELPFUL NOTES
If is often the case that
intermediate outputs do
not continue as
D, E, etc., but begin a new
sequence as shown here.
This can then be added to the Q column in the truth table below.
Input
This does not change the
logic behind each gate or
logic circuit.
ENRICHMENT
Can you write the output
in Boolean algebra?
WORD ALERT
Q
C
Intermediate outputs
Output
A
B
C
P = (A OR B)
Q = (NOT C)
X = (A OR B) AND (NOT C)
















































Worked Example
We already have a fire alarm that sounds in the building when the circuit detects heat and
smoke. However, we need a special alarm that will directly alert the fire service if there is no-one
in the building. This system uses three inputs to a logic circuit. The alarm X will sound if inputs A
(smoke) and C (heat) are both on, and where input B (motion detector) is off.
Detects: identifies.
Design a logic circuit and make a truth table to show when the fire alarm will sound;
i.e. where X = .
Solution
To show the conditions where X =  we must write the logic statements that represent
this situation.
X= , if (A =  AND B = ) AND (C =  AND B = )
To explain this a little further:
(A =  AND B = ) means A is ON and B is OFF
(C =  AND B = ) means C is ON and B is OFF
In Boolean algebra, we can write this as X = (A·B)·(C·B).
The logic circuit can be made up of Part  (A·B), which is (A =  AND B = ) as follows:
A
B
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Logic Gates and Circuits
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Chapter 10
Part  (C·B), which is (C =  AND B = ):
B
C
If we combine Parts  and , we get the circuit below:
A
B
REFLECT
C
Draw a combined
logic gate circuit which
includes a NAND gate and
create the corresponding
completed truth table.
To complete the circuit, we combine Parts  and  with the AND gate:
P
A
R
B
X
C
Q
The truth table can be constructed as follows:
Inputs
Intermediate outputs
Output
A
B
C
R
P
Q
X
























































Logic Gates and Circuits
SB CS PP.indb 153
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Chapter 10
Activity
Draw a truth table for this logic circuit:
P
A
HELPFUL NOTES
Add all possible input
combinations into
the truth table first.
Then decompose each
problem into smaller
sections to help complete
the intermediate outputs.
R
B
X
C
Q
Writing Logic Circuit Statements
You will need to be confident in writing and understanding logic statements. This logic circuit is for
an AND gate.
B
X
A
The AND gate logic circuit statement is written as X = A AND B. You can use these statements to
draw the corresponding logic circuits.
Logic gates can be combined to make more complicated circuits, such as this one below:
Worked Example
A
P
B
X
Work out the logic statement for this circuit.
Solution
154
SB CS PP.indb 154
Start at the final output, X. The X output depends on its inputs.
X = NOT P
P is an intermediate output, so we have to break it down into a mini
problem and put that into brackets. The P output depends on its
inputs.
P = (A OR B)
Now our logic statement only has the final output and the first inputs,
so we know it is complete.
X = NOT (A OR B)
Logic Gates and Circuits
14.5.21. 14:16
Chapter 10
Activity
Work out the logic statement for this circuit:
A
B
P
X
Q
C
D
Figure 7.2 Combined logic circuit with four inputs.
f
Start at the final output. The output of X depends on its inputs.
P is an intermediate output. Break it down and put it in
brackets. The P output depends on its inputs.
Q is also an intermediate output. Break it down and put it in
brackets. The Q output depends on its inputs.
Final output and the initial inputs
Drawing Combined Logic Circuits using Statements
You can draw a logic circuit directly from a logic statement. You may need to go back and revisit the
logic gate symbols first. For example, the logic circuit for the statement X = (A OR B) AND C is as follows:
A
P
B
C
X
This is possible by breaking down the statement and working through each stage.
X = P AND C
f
P = (A OR B)
X = (A OR B) AND C
HELPFUL NOTES
When converting a
circuit into a statement,
always start from the
final output and work
backwards . Convert each
intermediate output
into its inputs. When you
have only the first input
on the left and the final
output on the right in
your statement, you have
completed the table.
Remember to check you
have the right gates and
the correct number of
inputs.
Worked Example
We can also produce a circuit from a statement. For example, a car’s wipers will operate only
when the engine is on, the car is moving and the windscreen sensor is sensing rain.
There are three input conditions:
• the engine is on
• the car is moving
• the windscreen sensor is sensing rain
Solution
Let’s call them A, B and C.
The output is that the car’s wipers operate. This is X. We have to reduce three inputs to X for the
final gate. We do this by combining two inputs into one, like this:
X = A AND (B AND C)
Logic Gates and Circuits
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Chapter 10
The resulting logic circuit is this:
LINK
Consolidate your
understanding by
completing the Exercises
3-4 from pages 129-133
in the Workbook.
A
B
X
C
The truth table is this:
Inputs
Intermediate outputs
Output
A
B
C
B AND C
X








































Activity
A photocopier has two options for putting in paper to print: a place to slide in a single sheet of paper
and a multifeed drawer for a stack of paper. If there is paper in either of these places and we press
the start button then the photocopier will work. Make the logic statements to describe this scenario
and then draw the resulting logic circuit and truth table for the entire circuit.
ENRICHMENT
Can you think of other
logic circuits in use?
Logic Circuits in Use
In practice, logic gates are often built up using a combination of NAND gates.
NOT
A
AND
A
B
X
X
A
X
OR
B
156
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14.5.21. 14:16
Chapter 10
A
X
NOR
B
A
XOR
X
B
Worked Example
REFLECT
Show that the circuit below is logically equivalent to the NOT gate.
A
Why do you think the
NAND gate is often called
the ‘universal’ NAND Gate?
X
Solution
ENRICHMENT
Inputs
What careers/job roles do
you think require the use
of logic circuits?
Output
A
A
X






From the results given in the truth table, we can see that the truth table is logically equivalent to
the NOT gate, and the output X is the inverse of the two inputs of A.
Explain examples of
when these job roles
would have to use
this knowledge when
carrying out their work.
Activity
Show that the circuit below is logically equivalent to the AND gate.
A
B
X
In your home and in everyday life, there are many electrical items and appliances that rely on logic
circuits in order to function.
Consider the following scenario.
• In order for an elevator to travel to the correct floor, someone must have pressed a floor number
button inside the elevator and the doors must be closed.
• The total weight in the elevator must also be under the limit (false, , negative).
• The elevator moving = X (positive, , true).
Logic Gates and Circuits
SB CS PP.indb 157
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Chapter 10
The logic circuit for the scenario would look like this:
A
B
P
X
Q
C
And the logic statement would be:
X = (A AND B) AND (NOT C)
And the truth table would be as follows::
Inputs
A








B








Intermediate outputs
C








P= (A AND B)








Q = (NOT C)








Output
X








Writing logical expressions from Truth Tables
You can use a Truth Table to create the logical expression and create the logic circuit.
Using the Truth Table below where X is the output, we can see that both A and B need to be ON for
the output X to be ON. This tells us that the logic gate it is representing is the AND gate.
Look at each row and where the output (X) is ON () you look at the inputs (A and B).
• If the input is ON () then the input is written as the letter: A
• If the input is OFF () then the input is written as the letter with a line above it: A
158
SB CS PP.indb 158
A
B
X












AB
Logic Gates and Circuits
14.5.21. 14:16
Chapter 10
In the example above the output is ON () on the last row and both inputs are ON ().
• The logical expression would be written as X = A AND B
Notice that everything is in capitals, this is expected when writing logical expressions.
We can then draw the logic gate to represent the truth table and logical expression.
A
X
B
More than  inputs
Looking at the example below we can see the Truth Table shows an A, B and C input and an output X.
Inputs
A
B
C
X
































Look down the X column and circle where the output is ON ().
On each row where the output is ON (), use the method to note down which inputs are ON () and
OFF ()
The first row would be written as A B C
Inputs
A
B
C
X
































.
A B- - C
ABC
ABC
Logic Gates and Circuits
SB CS PP.indb 159
159
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Chapter 10
LINK
WB
Consolidate your
understanding by
completing Exercise 5,
page 133 in the
Workbook.
Row
Notes on inputs
Logical expression for row

ABC
NOT A AND NOT B AND NOT C

ABC
A AND NOT B AND NOT C

ABC
A AND B AND NOT C
Each part is placed within brackets and placed together with OR written between each.
The logical expression for the Truth Table would be:
X = (NOT A AND NOT B AND NOT C) OR (A AND NOT B AND NOT C) OR (A AND B AND NOT C)
160
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Chapter 10
7
Let’s Map It
Truth tables
Logic gates
have logic
states given by:
LOGIC
GATES
Boolean values
which are used
in truth tables:
Boolean
value
Binary
value
Synonyms
True

On
Yes
Positive
False

Off
No
Negative
Truth tables are used to represent
the Boolean expression of a logic
gate or logic circuit.
A
X
B
A




Inputs
B




Output
X




and in the different types of logic gates:
COMBINING
LOGIC
GATES
Types of gates
NOT
Input
A


Using Boolean
algebra:
AND
Output
X


A




Inputs
B




OR
Output
X




A




Inputs
B




Output
X




Boolean algebra
A
NOT A
A+B
A NAND B
A+B
A and B
A+B
A NOR B
A+B
A OR B
A
B
A XOR B
XOR
A




and by
combining
different logic
gates:
Inputs
B




NAND
Output
X




A




Inputs
B




NOR
Output
X




A




Inputs
B




Output
X




All have 2 inputs except for 'NOT' gate
Combining logic gates
B
P
X
A
Inputs
A




B




Intermediate
output
P




Output
X




Examples of logic circuits
used in the real world
-Security alarms
-Elevators
-Eletrical circuits
eg light switches
We can write
logic statements
for logic circuits:
-Bank vaults
Logic statements
Break down the
statements always
A
start with the
output
B
X = (A AND B) OR C
AND
P
OR
X
Logic
LogicGates
gates and
and Circuits
circuits
SB CS PP.indb 161
161
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14.5.21. 14:16
Chapter 10
Let’s Review

What logic gate matches these truth tables?
A
B
X
A
B
X

























Label the following logic gates:


Draw the logic circuit for the following statement X = (A AND B) AND (NOT C).
Complete a combined truth table including any intermediate outputs for the following: <?>
A
P
AND
B
OR
X
C

Draw the correct logic gate circuit and truth tables to match these Boolean algebra expressions:

A˙B
A+B
Ā
Draw the logic circuit diagram and corresponding truth table represented by the below Boolean algebra epressions.
Consider the logic statement:
X =  If [(A is NOT  OR B = ) NAND C is ] NOR [(A is  AND C is ) NAND B is ]
A
X
B
C
162
SB CS PP.indb 162
A
B
C
























Working space
X
Logic gates and circuits
14.5.21. 14:16
Answers
Answers to Let’s Review Sections
Chapter 
 Binary is a base- number system ( digits); Denary is
a base- number system ( dgits); Hexadecimal is a
base- number system ( digits)
 Accept either  or 
 
 Right to left
 Accept any correct method of working where the
answer runs as follows:
 -  – F
 Accept any correct method of working where the
answer runs as follows:
D –  – 
 Both methods enable the full use of bandwidth in
communication
 Data cannot be sent simultaneously
 Universal Serial Bus
 Any three sensible answers, including mouse, printer,
keyboard, hard disk drives, mobile devices
 Some packets of data could be lost, or some digits
could be changed
 Odd or Even
 False
 A check digit is calculated using all of the other digits
in a barcode and, if the code is correct, the check digit
should match
 Any three from: MAC addresses, error codes, HTML
colour codes and IPv addresses
 A timeout is where a receiving device is waiting for
a response and, once the timeout occurs, a repeat
request is made for the acknowledgement of the
expected data
 Accept either  or  =  (Denary)
 False
 Accept either  or  =  (Denary)
 The decimal part of the number is discarded
 Encryption is important to stop unauthorised users
intercepting and accessing sensitive data when it is
being transmitted across a network
 The use of two’s complement
Chapter 
 
 Architecture is the components that make up a
computer system
 The ‘most significant bit’
 
 American Standard Code for Information Interchange,
a character set used most commonly by computer
systems –  characters
 A kilobyte represents  bytes, a kibibyte represents
 bytes – a kibibyte is calculated by powers, whereas
a kilobyte is calculated by multiplying whole numbers
together
 Accept .Kb or .Kb
 Lossless compression – file sizes are reduced but there
is no loss of data, duplications are removed instead
Lossy compression – data is permanently removed
from a file to reduce its size, such as bits of music or
images
Chapter 
 A small chunk of data designed to be sent around a
network
 Packet header, payload and trailer
 The trailer tells the receiving device that it has reached
the end of the transmission. It is a validation check
 This is where a transmission of packets travels along a
network and takes different routes. Data is transmitted
by the most suitable route
 Serial transmission is where one bit at a time is sent
between devices, parallel transmission sends multiple
bits of data through multiple channels
 The CPU processes the instructions and data given by a
user through the input devices
 The Memory Address Register; Memory Data Register;
Accumulator; Program Counter; Current Instruction
Register
 The von Neumann architecture is based upon an
input device feeding data into a CPU, with a memory
unit reading data in and out of the CPU. The result of
processing is then sent to an output device
 Fetch – Decode – Execute
 Buses are connections that carry data around a
computer
 Cache memory sits within a CPU and holds instructions
and data that are needed regularly. Cache memory
allows quicker access to these instructions and data
leading to faster processing
 Dual-core
 Hertz, also accept gigahertz
 Any sensible example: dishwasher, GPS, sat-nav, central
heating, calculator, vending machine, lighting system,
CCTV
 A capacitive touchscreen allows multiple touch
sensing, a resistive touchscreen only allows one touch
due to using the pressure change, and infra-red works
on the basis of breaking a beam of light and is much
more sensitive
Answers
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 Either a moisture or level sensor would be acceptable
answers
 Cloud storage is when a user purchases some space on
an external server, accesses it via the world wide web
and can download from and upload to the space when
required
 A MAC address is a unique identifier for a piece of
equipment connected to the internet, the IP address
is the location identifier that enables devices to
communicate with one another
 These are issued by a router using a service called
DHCP, and are not specific to a device
 A router is a device that enables a home or business to
connect devices to the internet
Chapter 
 Any two of: the BIOS, utility software and the operating
system
 Any three of: managing peripherals, drivers, files,
multitasking, memory or handling interrupts
 Small applications which enable a computer to start all
of its devices
 An intervention from a user
 Software and hardware interrupts
 Either a division by zero or a process attempting to use
the same memory location
 Low level programming language is machine or binary
code. High level programming languages use words
that we use as humans
 It is easier for programmers to debug high level code
 Assembly language is similar to machine code but
it uses mnemonics for instructions and commands
alongside numbers
 A compiler and an interpreter
 A compiler will run an entire block of code and
produce a list of errors and is best used at the end of a
programming project. An interpreter will execute code
line by line
 It is better for debugging and finding problems as the
interpreter will stop when it finds an error
 Integrated Development Environment
 Any two functions from: code editing, auto-completion
of syntax, auto-correction of common errors, code
formatting, translation of code, error diagnosis and
simulation in a run-time environment
Chapter 
 The internet is the network of computers connected
together as a set of small networks to enable
communication to occur. The world wide web is the
collection of websites and web pages stored on servers
that are accessed through the internet
 Uniform Resource Locator
 Secure hypertext transfer protocol
 Any three from: displaying websites, bookmarks and
favourites, recording user history, multiple browsing
tabs, storing cookies, navigation tools and an address
bar
 Domain Name System
 The DNS Query uses the URL that has been entered by
the user and looks up the matching IP address. The IP
address then connects the user’s browser to the web
server that hosts the site and retrieves the required
website for the user to view
 Session and persistent cookies
 Any two of: cookies can store items in a shopping
basket for later, store preferences about how a website
loads, store login details or allow targeted adverts to
appear
 Any two of: Ethereum, Tether or Litecoin
 Blockchain is a database containing digital records of all
cryptocurrency transactions
 Any three of: brute-force attack, data interception,
DDoS attack, hacking, malware, pharming, phishing,
 Malicious software that causes damage to a computer
system
 Pharming is where a user is sent toa fake website that
looks genuine; phishing is where an email is received
that looks genuine but contains links to malicious
websites
 Where users are manipulated into behaving in a way
that they would not normally do
 This allows security loopholes to be closed and security
databases for anti-virus software to be kept up to date
 It enables browsing of the world wide web while
keeping an IP address secret
Chapter 
 Sensors, a microprocessor and actuators
 Actuators turn electrical signals into physical
movements
 Any sensible answer, for example automated motorway
signs that control the flow of traffic
 A danger of creating a fictional life where a user spends
more time rather than their real life
 A factory robot on a production line, a domestic robot
that operates in the home or an airborne robot like a
drone
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Answers
14.5.21. 14:16
 A mechanical structure or framework, and electrical
components, like sensors, microprocessor and
actuators
 Any sensible example, such as a scanner in a CT
scanning machine
 A trace table enables a programmer to work through
the code on paper, line by line, to check where
variables, selection, sequencing and iteration take
place
 A syntax error
 They can carry out jobs without humans needing to be
present
 Any reasonable error, such as incorrect use of an
arithmetic or Boolean operator
 Artificial Intelligence
Chapter 
 Expert Systems and Machine Learning
 A variable piece of data can be changed in some way,
either by the user or the program
 Any reasonable explanation, such as: A user would
type a word into the user interface and select the
language of translation. The software would use the
inference engine to determine what was required and
would then draw upon its knowledge base to provide
a solution. The translation may also utilise the rules
base and explanation system to also provide possible
alternatives to the translated word, based on similar
searches previously carried out by other users
 Any two from: integer, real, char, string or Boolean
 The sequence determines the order that a set of
instructions are carried out
 An IF statement
 Count-controlled, pre-condition and post-condition
loops
Chapter 
 A counter is used to know how many times the
iteration has occurred
 Analysis – Design – Coding – Testing
 Changing them into upper or lower case
 Abstraction is the process of selecting the information
in a problem and focusing only on the important parts
of that information. During abstraction, any detail that
is irrelevant to the problem is ignored
 Any three from: subtraction, division, raise a power,
MOD or DIV
 Decomposition is breaking down a complex problem
into small manageable pieces. It is where a problem
becomes a series of small tasks that can be handled first
individually and then collectively as part of the bigger
program
 A decision, usually a yes/no answer
 False
 Structure diagrams are different from flowcharts in that
they display the different levels of detail within a set of
decomposed problems
 All items of data in a set are looked at until the program
matches the piece of data it is looking for. Once this
match is obtained, the search is completed. In a large
data set this would take a long time
 A data set that has not yet been sorted into a particular
order
 A bubble sort is based upon the idea of swapping
adjacent items in a data set until the set is in a desired
order
 Any three answers from: range check, length check,
presence check, format check, check digit
 Double-entry checking
 The process of testing reports any errors to the
programmers and the testing is repeated until there are
no errors found in the system
 Does not equal
 AND - If something and something else are true or
false; OR - If something or something else is true or
false; NOT - If something is NOT true or false
 Where it is necessary to execute one IF statement,
followed by another, followed by another. This would
form a subroutine, with each routine nested inside
another
 Where a function or procedure sometimes requires a
programmer to give them additional information to
carry out their processes
 A global variable is generally declared at the start of
a program and can be used anywhere throughout a
program. A local variable is declared within a function
and can only be used within the function
 Any two from: MOD, DIV, ROUND, RANDOM
 All identifiers should be easily recognisable by
programmers to ensure the code can be easily read
and understood
 Commentary can be very helpful to know what a
programmer or developer was thinking at the time
of writing a particular line or set of lines of code, and
any programmer working in a team would be able to
access other people’s coding much more easily. They
are not executed
 A set of related data that are all of the same data type
 False
 This data includes the extreme values of the normal
range given, as the highest possible and lowest
possible data in a set
Answers
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 It is often important to store program data in external
files so that it is not lost when a program has finished
running. Programming can often take weeks and
months to create, and to be constantly restoring data
to code would be hugely time consuming
 False
 Practical task - answers may vary
 Practical task - answers may vary
Chapter 

Chapter 
OR gate
 A database is an organised collection of data. It is
electronically stored and accessed in a computer
system

NAND gate
Flat-file database
Relational database
A flat-file database stores
simple data formats. They
store only a single table of
data.
The information given by a
record is complete with a
fixed number of fields.
Thus, the database is not
related to any other table or
database.
This method of storing data
is not efficient and may
lead to problems like data
duplication, data redundancy
and input errors.
A relational database can have
multiple related tables.
When the tables are linked,
the user can work on complex
data structures having
multiple tables.
A relational database does not
allow data duplication. Also, it
is more efficient and
consistent than a flat-file
database.

NAND gate
NOR gate
XOR gate
 The logic circuit for the scenario would look like this:
 Queries are used for working with data in a database.
These are requests that help in arranging, retrieving or
modifying information from a database.
Example of statement that can be used to retrieve data
using SQL queries:
SELECT [Field Name] FROM [Table Name]
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SB CS PP.indb 166
 X = P OR C
P = A AND B
 A data type is an attribute or property of a field
in a database which helps in helps the computer
to identify similar data for the purpose of sorting,
searching and calculation. For example, Text, Char,
Integer, Number, etc.
X = (A AND B) OR C
A
B
 Practical task - answers may vary
0
0
 Validation refers to checking and confirming the
accuracy of data or information in the computer
system. There are certain rules that are followed when
data is typed into a database system called the data
validation rules. For example, a phone number does
not contain a character or an alphabet. These rules help
in accepting the data which are as per the set format.
The data entered into a database can sometimes be
entered incorrectly. It can be invalid, inconsistent or
incomplete. To avoid any such issue, the user may apply
different validation checks. Some validation checks are:
Presence check, Range check, Length check and so on.
0
0
The truth table is:
Input
Intermediate outputs
Output
C
A AND B
X
0
0
0
0
1
0
1
1
0
0
0
0
1
1
0
1
1
0
0
0
0
1
0
1
0
1
1
1
0
1
1
1
1
1
1
1
Answers
14.5.21. 14:16
 A . B represents AND gate, that is, A AND B
 The corresponding circuit diagram is:
The corresponding Logic gate and circuits are:
The truth table is:
Input
A + B represents OR gate, that is, A OR B
The corresponding Logic gate and circuits are:
Intermediate outputs
Output
A
B
C
P=Ā
Q=P
OR B
R=Q
NAND C
S=A
AND C
T=B
NAND S
X=R
NOR T
0
0
0
1
1
1
0
1
0
0
0
1
1
1
0
0
1
0
0
1
0
1
1
1
0
1
0
0
1
1
1
1
0
0
1
0
1
0
0
0
0
1
0
1
0
1
0
1
0
0
1
1
1
0
1
1
0
0
1
1
0
1
0
1
1
1
0
1
0
1
0
1
represents NOT gate, that is, NOT A
The corresponding Logic gate and circuits are:
Answers
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Index
A
abstraction 95
Access 132–133
access levels 74
accumulator 36
actuators 48, 84, 85
address bar 29, 68, 69, 70
address bus 36, 37
adware 73
AI (artificial intelligence) 88–90
algorithms 28, 94, 100–101, 114
flowcharts 97–98
iteration in 115
pseudocode 98–99
solution methods 101–103
structure diagrams 99–100
trace tables 105–107
writing 108
ALU (arithmetic logic unit) 35, 37
analogue signals 14, 44
AND gate 143, 144
AND operator 119
application software 60
running sequence 61
arithmetic operators 118
ARQ (automatic repeat requests) 28
arrays 122–123
ASCII code 13
assembly language 63
authentication 75–78
biometric 77
electronic tokens 78
magnetic stripes 77
passwords 75–76
physical tokens 78
smart cards 77
spyware 76
zero login 77
auto-completion 64
auto-correction 64
automated systems 84–86
automating software updates 78
AutoNumber 130
AVERAGE 103
B
barcode
check digits 28
reader 44
binary numbers 2–3
adding two binary numbers 7–8
converting to denary 4
dividing 10
multiplying 9
overflow errors 8–9
binary shifting 9
with 8-bit binary numbers 10–11
168
SB CS PP.indb 168
biometric authentication 77
BIOS (Basic Input Output System) 60
bit (binary digit) 15
bit depth 15
bit rate 15
Blu-ray discs 53
bookmarks 70
Boolean algebra 142–143, 144, 145,
147, 148
Boolean data 112, 130
Boolean operators 107, 119, 142
boundary data 105
browsers 70
brute-force attack 72
bubble sort 101–103
buses 36
bytes 5, 15, 16
C
cache memory 38
cameras 43
capacitive touchscreens 43
capacitors 52
CASE statements 114–115
CD (compact disc) drives 53
Character/Char, data type 112, 129
check digits 28–29, 104
checksum 28
clock speed 38
cloud storage 54
code editor 64
comments, in computer programs
121
compilers 63–64
computer architecture 34–36
computer systems 60, 97–100
embedded 39
OS (operating system) 60
constants 112
control bus 36
control unit 35
cookies 70, 71
COUNT function 137
count-controlled loop 115, 116
counting 103, 117
CPU (central processing unit) 34
processing cores 38
cryptocurrency 72
currency, data type 130
current instruction registers 36
cyber security 72–80
brute-force attack 72
data interception 72
DDoS (Distributed Denial of Service) attack 73
hacking 73
malware 73
pharming 74
phishing 74
social engineering 74
solutions 74–80
D
data 128
abnormal 105
corruption 27
types 112, 129
data bits 3
data bus 36
data compression 18
data entry, validation and verification
104–105
data interception 72
data storage 15–17, 50–53
data transmission 22–27
full-duplex 25–26
half-duplex 25
methods of 23–26
parallel 24
serial 23–24
simplex 24
vis USB 26–27
databases 128–130
creating 131–134
data types 129
data validation 133–134
entering data 134
queries 129, 135–137
tables 129, 132–133, 134
types of 130–131
uses 128
date/time, data type 130
DBMS (Database Management
System) 130
decomposition 95
DEFAULT output 115
denary (base-10) numbers 2
converting to binary 3–4
converting to hexadecimal 5
dictation software 44
digital currency 72
digital light processing (DLP)
projector 46
Distributed Denial of Service (DDoS)
attack 73
DIV (division) 118, 121
Domain Name System (DNS) Query
71
double entry 105
DO-WHILE iteration 116
dual-core processor 38
DVD (digital versatile disc) drives 53
Index
14.5.21. 14:16
E
echo check 28
electronic tokens 78
embedded systems 39
encryption 29–30
asymmetric 30
symmetric 30
error detection 27–29
and correction 107–108
error diagnostics 64
executable files 63
expert systems 89
extreme data 105
F
favourites 70
fetch-decode-execute cycle 37
fields, in a database 129
file handling 123–124
files
reading from 124
writing to 124
firewalls 79–80
flash drives 52–53
flat-file (single-table) databases 130
flowcharts 97–98
FOR loop 116
foreign key 130
format check 104
fragmentation 51
full-duplex data transmission 25–26
functions 120, 121
G
gaming controllers 41
global variables 121
H
hacking 73
half-duplex data transmission 25
hardware interrupts 62
HDMI (high-definition multimedia
interface) 46
hertz 15
hexadecimal numbers 3
converting to denary 6
uses in data representation 6–7
HTML (hypertext markup language)
70
HTTP (hypertext transfer protocol) 69
https (secure hypertext transfer
protocol) 69
I
IDE (Integrated Development
Environment) 64
IF, THEN, ELSE 114
IF statements 114
image files, calculating the file size
of 16
image representation 15
information 128
infra-red screens 43
inkjet printers 47
input 113
input devices 40–45
instruction sets 38–39
integers 112, 129
internet 68–71
interpreters 63–64
interrupt service routine 61
interrupts 61–62
IP (Internet Protocol) address 22,
55–56
ISBN numbers, check digits 28
iteration 115–116, 120
J
JavaScript 63
jpeg files 18
K
keyboard 40
kibibytes (KiB) 16
L
LAN (local area network) 56
laser printers 47
LCD (liquid crystal display) monitors
45
LCD (liquid crystal display) projectors
46
LED (light emitting diode) screens 45
length, of a string 117
length checks 104
library routines 121
linear search 101
local variables 121
logic circuits 150–158
drawing 155–156
with more than two inputs
151–154
using 156–158
writing statements 154–155
logic errors 107
logic gates 142–149
combining 150–158
types of 143–149
logical operators 118–119
lossless data compression 18
lossy data compression 18
LOWER 118
M
MAC (media access control)
addresses 55
machine code 62
machine learning 90
magnetic hard disk drives 51–52
magnetic stripe cards 77
malware (malicious code software) 73
anti-malware software 74–75
MAR (memory address register) 36
MAXIMUM 103
MDR (memory data register) 36
measurement units 16
memory 50
memory unit 36
microphones 44
microprocessors 49, 84, 85
MINIMUM 103
MOD (modulo) 121
modems 56
monitors 45
mouse 41
mp3 files 18
N
NAND (NOT AND) logic gate 52, 146,
147
nested statements 119–120
iteration 120
selection 119
network hardware 54–56
nibbles 15
non-volatile storage 51
NOR (NOT OR) logic gate 52, 146, 147
normal data 105
NOT Boolean operator 119
NOT logic gate 143, 144
number systems 2–3
numbers/numeric data 129
numeric keypads 40
O
opcodes (operation codes) 38
operands 39
optical character recognition 43
optical disc drive 53
OR Boolean operator 119
OR logic gate 143, 144–146
ORDER BY clause 137
OS (operating system) 60–61
output 113
output devices 45–48
overflow errors 8–9
P
packet switching 22–23
packets, structure 22
parallel data transmission 24
parity check 27–28
passwords 75–76
pen drives 52–53
pharming 74
phishing 74, 79
pixels 15
pointing devices 41–42
portable magnetic hard drives 52
portable solid state hard drives (SSDs)
52
post-condition loops 115, 116
pre-condition loops 115, 116
Index
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14.5.21. 14:16
presence checks 104
prettyprint 64
primary key 130, 133
primary storage 50
printers 47–48
privacy settings 80
procedures 120–121
processing core 38
program counter 36
program development life cycle 94–96
analysis 94–95
coding and iterative testing 96
designing 95–96
testing 96
programming
concepts 112–122
creating programs 121–122
fundamentals 114–119
programming languages 62–64
high-level and low-level 62
proxy servers 80
pseudocode 97, 98–99
Python 63, 94, 108, 112, 113
arrays 122
functions 120
iteration 116
nested selection 119
reading from a file 124
string handling 117–118
totalling and counting 117
writing to a file 124
Q
QR (quick response) scanner 45
quarantine 75
queries, database 129, 135–138
query-by-example 135–136
R
RAM (random access memory) 36,
50, 53
RANDOM 121
range checks 104
ransomware 73
reading from a file 124
real numbers 112, 129
records 129
registers 35–36
relational databases 130
resistive screens 42
robotics 87–88
ROM (read only memory) 50
ROUND 121
routers 56
run length encoding (RLE) 18
run-time environment 64
170
SB CS PP.indb 170
S
sample rates 15
SATA (serial advanced technology
attachment) cable 51
scanners 43
secondary storage 50, 51–53
SELECT statement 137
selection 114
sensors 49, 84, 85
sequencing 114
serial data transmission 23–24
simplex data transmission 24
smart cards 77
social engineering 74
software 60–62
application 60, 61
automating updates 78
OS (operating system) 60–61
software interrupts 62
solution methods 101–103
sound files, calculating the file size of 17
sound representation 14–15
speakers 48
spelling errors, in phishing emails 79
spyware 73, 76
anti-spyware software 74–75, 76
SQL (Structured Query Language) 135,
136–137
SSD (solid state hard drives) 52
SSL (secure sockets layer security
protocol) 80
standard solution methods 103
strings 112, 117–118
structure diagrams 97, 99–100
stylus pens 41
substring 117
SUM function 137
symmetric encryption 30
syntax errors 107
system security 61
system software 60
T
tables, in a database 129
testing programs 105
text representation 13–14
text/alphanumeric data 129
three-dimensional (3D) printers 48
tokens 78
totalling 103, 117
touch screens 42, 46
touchpads 41
trace tables 105–107
trackballs 41
transistors 3, 52
translators 63, 64
trojan horse 73
truth tables 143
two’s complement 11–13
type checks 104
U
Unicode 14
units of measurement 16
UPPER 118
URL (Uniform Resource Locator)
68–69, 79
USB (Universal Serial Bus) 26–27
user history 70
utility software 60
V
validation checks
for data in databases 133–134
for programs 104
variables 112
in computer programs 121
global 121
local 121
verification 105
video conferences 43
virtual memory 53
viruses 73
anti-virus software 74–75
visual checks 105
von Neumann, John 35
W
web address see URL (Uniform
Resource Locator)
web browsers 70
web pages 71
webcam (web camera) 43–44
WHERE clause 136
WHILE loop 116
world wide web 68
worms 73
writing to a file 124
X
XOR gate 146, 148
Z
Zero login 77
Index
14.5.21. 14:16
Computer Science Glossary
Adjacent (page 101): the item next to another item
Algorithm (page 94): a set of rules or instructions for
solving a problem
Alphanumeric (page 76 ): text on page simply reads
‘letters and numbers’
Ambient (page 49): the immediate Surroundings
Amplitude (page 14): the strength of a sound wave,
measured at the highest level
Analogue (page 14): using signals or information
represented by a continuously variable physical
quantity
Combination (page 142): a joining of different parts
or qualities
Comparisons (page 101): checking one item against
another and looking for differences or similarities
Complex (page 150): more difficult / more
components involved
Comprise (page 96): include, be made up of
Components (page 85): pieces of equipment in a
system
Compromise (page 74): become vulnerable or
function less effectively
Analogue signals (page 44): continuous signals that
cannot be processed by a computer until they
Condition (page 145): the state of something in
relation to its appearance, quality or working order
are converted into digital data.
Conductive (page 43): heat and electricity can pass
through an object
Array (page 45): a data structure that holds related
data.
Architecture (page 34): how a computer system is
designed, including the rules and methods that the
system should follow
Control bus (page 37): a bus that carries instructions
from the CPU to control the actions of the computer
Computational thinking (page 95): breaking down a
problem into smaller sub-problems to solve them
Arithmetic (page 142): use of numbers to calculate
an outcome
Corruption (page 27): where something is altered or
changed without a user knowing
Automated (page 84): machines carrying out a job
that would otherwise have been done by humans
Constructs (page 114): the building blocks of
programming
Bandwidth (page 18): the transmission capacity of a
computer network
Criteria (page 129): conditions or questions
Barcode (page 28): a machine readable code in
the form of numbers and a pattern of parallel lines
of varying widths, printed on a physical item. This
pattern identifies it from other barcodes
Data duplication (page 130): a process of creating an
exact copy of data
Data redundancy (page 130): the storing of the
same data in multiple locations
Binary (page 2): a number system that contains just
2 numbers, 0 and 1, and the number system that a
computer uses to process data
Data validation rules (page 133): these are some
rules which help the user to know that the data
being entered in a database is correct
Bluetooth (page 40): a form of wireless connection
for connecting devices together when they are
Debugging (page 64): finding errors or mistakes in
code
near each other
Decipher (page 30): converting code into normal
language
Boolean (page 107): where a variable can have one
of two values, true or false
Degrades (page 53): breaks down or deteriorates
Brainstorming (page 94]: an exhaustive discussion to
solve problems or generate ideas
Capacitor (page 52): a small electronics device that
stores an electrical charge
Detects (page 152): identifies
Dictation (page 44): the process of reading words
into a microphone so that they can be converted
from analogue signals to digital words on a screen
Computer Science Glossary
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Division by zero (Page 62): a mathematical
calculation that has no answer, and one that is
automatically rejected by a computer for this reason
Efficiently (page 2): to perform something in a wellorganised and competent way
Electrodes (page 43): a conductor where electricity
enters or leaves an object
Electromagnetic (page 51): the electrical and
magnetic forces or effects produced by an electric
current.
Entity (page 129): object or thing
Equivalent (page 142): the same or equal meaning
Address (Page 22): a unique string of numbers
separated by full stops that identifies each computer
using the protocol to communicate over a network
Intervention (page 61): an action taken by someone
to make something different happen
Intricate (page 34): very complicated or detailed
Inverted (page 12): reversed or transformed into its
corresponding opposite
ISBN number (page 28): International Standard Book
Number, a global system for identifying individual
books. ISBN numbers have 13 digits
Firmware (page 60): small applications which enable
a computer to start all of its devices
Hertz (page 15): frequency of samples, measured in
cycles per second
Floating-point (page 112): a number in
programming that contains a decimal point, and the
decimal point can ‘float’ in different places to help
with handling large numbers
Interrupt service routine (page 61): a software
routine that hardware invokes in response to an
interrupt
Formally (page 143): officially / explicitly
Function (page 120): a block of organised, reusable
code used to perform a single, related action
HDMI (page 45): high-definition multimedia
interface technology displays high-definition
images and sound through a single cable. HDMI is a
standard connection port for audio/visual devices in
computers
Hexadecimal (Page 55): a number system that uses
16 characters instead of the 10 characters used in
the decimal system or the two used in binary
Hypertext transfer protocol (page 69): the agreed set
of rules that all computers use for transmitting files
(data) over the world wide web
Impaired (page 15): weakened or damaged
Increment (page 117): to increase by a set number
Inefficient (page 113): not the best or fastest way of
achieving a goal
Infinitely (page 85): continues forever, until stopped
SB CS PP.indb 172
Internet Protocol (IP)
Executable (page 63): a file that launches and runs a
series of code when opened
Foreign key (page 130): A foreign key is a fi eld or
combination of fi elds that are related to the primary
key of another table
172
Interface (page 47): a device or program used to
communicate with a computer
jpeg (page 18): Joint Photographic Experts Group:
the organisation that created the file type
Lightning connection (page 52): a high-speed
connection that was developed by Apple for the
purpose of connecting multiple external devices to
their computers
Logic gates (page 142): the basic units of a digit
circuit that control the flow of electronic signals
Logical reasoning (page 89): a set of reasonable
conclusions and explanations
Microprocessor (page 49): Microprocessors are
integrated circuits that contains all the functions of
a CPU of a computer
mp3 (page 18): MPEG (Moving Picture Experts
Group: the organisation that created the file type)
Layer 3
Negotiations (page 94): a discussion to produce a
settlement or agreement
Nibble (page 5): a set of four binary bits
Originator (page 22): the sending Device
Operating system (page 41): a piece of software that
communicates with the hardware and allows other
programs to run
Computer Science Glossary
14.5.21. 14:16
Overflow (page 9): the generation of a number or
other data item that is too large for the assigned
location or memory space
Parity (page 23): ensuring that something is the
same
Parity check (page 27): is a bit added to a string of
binary code as the simplest form of error detecting
code
Perspective (page 94): a particular way of thinking
about something
Pictorially (page 100): in the form of a Diagram
Pixel (page 15): a tiny area of illumination on a
display screen
Platter (page 51): a circular magnetic plate that is
used for storing data in a hard disk.
Portability (page 53): the ability to carry or move
something
Powers (page 2): the product obtained when a
number is multiplied by itself a certain number of
times
Pressure (page 49): continuous physical force
exerted on an object
Primary key (page 130): A primary key is a unique
field that allows the user to identify a record
Protocol (page 27): a set of rules that are applied to
the transfer of data
Pseudocode (page 98): a version of programmable
code written in standard English
Quarantine (page 75): to place into isolation
Referred: (page 143) denoted / identified
Remainder (page 3): the number left over in a
division in which one quantity does not exactly
divide another
Replicating (page 90): creating as close to a copy of
something as possible
Search engine (page 70): a web-based tool that is
used to find web pages based on a given topic or
keyword entered by the user. It then returns a list of
relevant web pages and their respective URLs
Serial advanced technology attachment (SATA)
( page 51): a type of cable usually found inside
computers. It connects a hard drive with the
motherboard
Shift (page 9): movement either to the left or right
Simulate (page 64): run a test version of an
application
Simultaneously (page 25): at the same time
Sophisticated (page 75): more complex
Sound card (page 48): an internal device of a
computer that provides a method of input and
output of audio signals for use with multimedia
applications
Spoof (page 74): something that is fake but pretends
to be genuine
String (page 129): a set of characters that can also
contain spaces and numbers
Stylus (page 41]: a pen that can be used either
directly onto a screen or a pad connected to a
computer
Substitute (page 76): exchange for something
different
Syntax (page 64): the structure of not just
statements but also symbols, punctuation, etc., in a
computing language
Test strategy (page 96): test plans for testing the
system
Transaction (page 29): the process of buying or
selling something
Translated (page 63): changed into a different
language
Transistor (page 3): a small electronics device that
carries, switches and amplifies an electrical current
Truth tables (page 144): used to represent the
Boolean expression of a logic gate or logic circuit
Ubiquitous (page 26): located everywhere
Universal serial bus (USB) (page 40): a standard
connector found on many different types of
computer and used to connect external devices
Utility (page 60): a small piece of software that
controls specific parts of the hardware
Validation (page 104): the process that helps the
system know the data entered is correct
Validation check (page 104): testing for validations
Computer Science Glossary
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Video conference (page 43): a form of visual
communication where users in different places can
see, hear and speak to each other using a variety of
equipment, including web cameras, monitors and
microphones
174
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Visualise (page 95): to be able to see a prototype of
an idea
Volatile (page 50): loses its contents when there is
no electrical charge
Computer Science Glossary
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14.5.21. 14:16
Cambridge IGCSETM
Computer Science
For over 60 years Marshall Cavendish Education has been
empowering educators and students in over 80 countries with
high-quality, research-based, Pre-K-12 educational solutions.
We nurture world-ready global citizens by equipping students
with crucial 21st century skills through our resources for schools
and education centres worldwide, including Cambridge schools,
catering to national and international curricula.
The Marshall Cavendish Education Cambridge IGCSETM Computer Science series
is designed for students studying for the Cambridge IGCSE and IGCSE (9–1)
Computer Science syllabuses (0478/0984). The series focuses on developing
important computer science skills relevant to real-world applications.
SB
The Student’s Book:
• Encourages active and inquiry-based learning through hands on activities and discussions
• Supports subject literacy with concise language, language support and bite-sized concepts
• Caters to the international landscape with multicultural photographs, visuals and other references
• Promotes visual learning through concept infographics and clear illustrations
• Includes mind maps and links that build learners’ understanding of the relationships between concepts
• Nurtures life-long learning in building digital literacy skills which students can use beyond their course
• Helps students develop 21st century competencies, so that they become future-ready
✓ Supports the full Cambridge IGCSE and IGCSE
(9–1) Computer Science syllabuses (0478/0984) for
examination from 2023.
✓ Has passed Cambridge International’s rigorous
TM
Computer Science
STUDENT’S
BOOK
STUDENT'S BOOK
This resource is endorsed by
Cambridge Assessment International Education
Cambridge
IGCSE
Series architecture
• Student’s Book
• Workbook
• Teacher’s Guide
• e-book
quality-assurance process
✓ Developed by subject experts
✓ For Cambridge schools worldwide
ISBN 978-981-4941-59-4
Greg Shilton
Megha Goel
9 789814 941594
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