Computer Science 1
Computer systems
SarahLawrey
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EDUCATION
LEARN MORE
Software and software development
Software ................................................... ‎‫ ااا‬9
Applications generation .................................. ES12
Software development .................................... e 14
Types of programming language....................... e 16
Exchanging data
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Compression ................................................
Encryption .................................................2 a 24
Hashing ..................................................2 ‎‫ ل ل ع ل ا‬42
AI, o 25
Networks .................................................... ES 28
The internet 2 ES 31
Data types, data structures and Boolean algebra
Data types ................................................... ES 36
Data structures .............................................. ES 40
Boolean algebra .......................................... o 42
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Computer systems
The central processing unit (CPU)...................... e 3
Types of processor ....................................... o 4
Input, output, storage and memory.................... o 5
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Contents
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Computer law and ethical, moral and social issues
Computer law ............................................. ‎‫ ل‬ES 46
Ethical, moral and social issues ......................... AN46
This workbook will help you to prepare for the
Computer Science Computer Systems exam.
Youstill need to read your textbook and refer to your
Your exam will include a range of questions
requiring short and long responses. You will also
have extended response questions.
Content specific to A level only is indicated by a red
line in the margin.
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For each topic of the exam there are:
revision guides and lesson notes.
Marks available are indicated for all questions so
that you can gauge the level of detail required in your
stimulus materials including key terms and
concepts
answers.
style questions
space for you to write or plan your answers.
Timings are given for the exam-style questions to
make yourpractice as realistic as possible.
short-answer questions that build up to exam-
Answering the questions will help you to build
your skills and meet the assessment objectives AO1
(Demonstrate knowledge and understanding), AO2
(Apply knowledge and understanding), AO3 (Design,
program and evaluate computer systems).
Answers are available at:
www.hoddereducation.co.uk/workbookanswers
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Computer systems
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The central processing unit (CPU)
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The central processing unit (CPU) is a fundamental part of a computer system.It is responsible for fetching every
instruction given to the computer, decodingit and executingit. It is a very active componentthat is capable of
processingbillions of instructions per second.
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The CPU has a numberofdifferent componentsthatit uses to processinstructions. A single cycle of processing an
instruction is called the fetch-decode-execute cycle. Three main factors can affect the performance of a CPU: clock
speed, numberof cores and cache size.
A CPU will have a particular structure, such as the von Neumann or Harvard architecture. The CPU is small in size
but has a very big role to play.
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Pipelining
Most CPUs makeuse of pipelining. This allows the CPU to processan instruction whilst fetching the next instruction.
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Types of processor
There are different types of processor: two of these are CISC and RISC.
CISC processors often contain a large set of instructions for both simple and complex procedures. CISC processors
have separate instructions for each task that the processor could be required to do.
RISC processors use a highly optimisedset of instructions that are designed to require fewer cycles per execution of the
instruction. RISC processors often contain a smaller set of instructions comprised of those that are the mostfrequently
used. Unlike CISC processors, RISC processors normally have several tasks condensed into a single instruction.
The speed of the processor can be increased usingparallel processing. This is when a processor can carry out
multiple tasks simultaneously. Two types of parallel processing are SIMD and MIMD.In SIMD processing, the
sameoperation is performed on multiple data simultaneously. This is useful for improving the performance
of the processor with multimedia. In MIMD processing, different instructions are performed on different data
simultaneously. A processor needs to be multicore to allow MIMDprocessing.
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Graphics processing unit (GPU)
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GPUsare designed to processcalculations for graphics. They have aninstruction set specifically designed for
this. GPUs will often use SIMD processing. The capabilities of GPUs are sometimes used for more than processing
graphics. GPUs are now usedfor tasks such as crypto-currency mining, cracking passwords and machine
learning.
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Input, output, storage and memory
Many computer systems have input, output and storage. Computer systems often have RAM and ROM storage.
RAM is volatile; this means the contents are lost when power is disconnected. ROM is non-volatile; this means the
contents are retained when poweris disconnected. RAM is used to store the programs and data that are currently
in use, while ROM is usedto store the boot-up instructions.
There are three maintype of storage: magnetic, flash and optical. Magnetic storage devices use magnets to record
data on rotating magnetic plates. An example is a hard disk drive. Flash storage devices use positive and negative
charges to record data onto cells that are made up of transistors. Unlike magnetic storage devices,flash storage
devices do not have any moving parts. An example is a solid-state drive. Optical storage uses a beam oflight and a
lens to record data onto a disk. Data is stored in pits and lands on the surface of the disk. An exampleis a CD.
Another wayofstoring data is using virtual storage. Virtual storage is when data is stored in a cloud-based system
and accessed using an internet connection. The alternative would bestoring data locally on the computer. Virtual
storageis only virtual in name;it is still physical storage and is normally owned and managedbya third party.
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0 Tina has a computer system that has a dual core, 2 GHz processor. She wants to upgrade her
processoras she has a new job that requires her to use her computer for high-quality video
editing.
Explain the upgrades she can make to the processor and what effect it will have on
the performance.
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The operating system is software that gets loaded by the computer after it has booted up. The boot-up routineis
normally carried out by the BIOS. The BIOS will usually carry out the POST test and oncethis is complete it will
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boot the computer. The operating system is then loaded into memory.
The operating system is software that is designed to control and manage the hardware in and connectedto the
computer, and all other software. It is responsible for tasks such as file management, memory management,
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operating system, it would be very difficult, if not impossible, to use a computer system. Operating systems are
usually required to communicate with several different devices. These devices are often manufactured by different
companies. This can cause communication issues. To allow communication to occur between the different devices
and the computer system, software called drivers are used.
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Different types of operating system
There are a several different types of operating system. These includedistributed, embedded, multi-tasking,
multi-user and real time.
A distributed operating system involves a group of computers working together on a single task. Each computer
is responsible for part of the task. A distributed operating system is used to co-ordinate the computers to enable
them to complete the task. An embedded computer, such as a washing machine, may have an embeddedoperating
system. This kind of operating system is more specifically tailored for the embedded computer,to increaseefficiency.
A multi-tasking operating system is one that can run several programs simultaneously. This is the most common
type of operating system found on the computers we usein ourdaily lives. It allows us to do tasks suchaslisten to
music whilst typing into a document, occasionally checking oursocial media.
A multi-user operating system is one that allows multiple users to be using the computer's resources
simultaneously. This type of operating system often exists on a mainframe computer, where many users may be
accessing the data at a given time.
A real-time operating system is one that has a rapid responsetime. It completes the action requested within a
fraction of a second.
It is possible for a computer to have more than one type of operating system. For example, the computers we use
on a daily basis will most likely be both multi-tasking and real time.
O A washing machine uses an embedded operating system. Identify three other devices
that would use an embedded operating system.
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Memory management
One responsibility of the operating system is memory management. This includes how the memory resources
available in the computer are shared. One type of memory management that a computer can useis paging. Paging
is when a computer retrieves data stored in secondary storage and bringsit into RAM. In paging, the memoryis
divided into physical units of the same size. Each of these units is known as a page. Another type of memory
management is segmentation. In segmentation, the memory is divided into logical units of varying size. Each of
these units is known as a segment. Each segmentwill normally be a logical grouping of code, such as a procedure.
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Interrupts
An interrupt does exactly whatis soundslike it should,it interrupts! This service is needed because a computer needs
to know whento giveits attention to a different task. A device sends a signal to the CPU;this signal is known as an
interrupt. Each interrupthasa level of urgency and the operating system manages whichinterruptsignals will be dealt
withfirst. The operating system has a function called an interrupt service routine that carries out this responsibility.
Scheduling
An operating system that is multi-tasking needs to make sure that tasks are run simultaneously.It is important
to understandthat they aren't actually run simultaneously; the computer switches between them during fractions
of seconds to make them appearto be run simultaneously. For this to occur an operating system needs to have
a scheduler. A scheduler managesthe timeallocated to the different tasks a CPU is currently processing.It can
use several different algorithmsto do this, these include roundrobin,first comefirst served, multi-level feedback
queues, shortestjob first and shortest remaining time.
Virtual machines
A virtual machineis effectively creating a computer within a computer. It is a piece of software that is run ona
computer, but is designed to behavelike a different computer. A commonapplication ofthis is to have multiple
operating systems on a single computer. Each operating system will be a virtual machine.
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Applications generation
Applications are the programs that we use daily to complete our everyday tasks. Some examples of application
software are a word processor, a spreadsheet package, a web browser and utility software.
Utility software normally has a small, dedicated purpose, for example defragmenting the hard drive, scanning for
viruses, compressing files or creating backups. Utility software is designed to maintain a computer system.
Applications can be open source or closed source. When software is open source, the source codeforit is freely
accessible to anyone. This means that users can modify the code to changethe functionality of the software.
When software is closed source, the source codeis not accessible to anyone but the creator. There are benefits
and drawbacksof both open source and closed source software. One benefit of open source softwareis thatit is
mostly free (without cost). One drawback of open source software is that it may not have been tested properly if the
resources are not available to do this. One benefit of closed source softwareis that it has been thoroughly tested
before release. However, one drawback of closed source softwareis that it can be expensive.
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Assemblers, compilers and interpreters
When a programmercreatesan application, a translator is needed to convert the program to machine code. This
is because processors only understand machine code. Depending on the language the programmerhas used, an
interpreter, a compiler or an assemblerwill be used.
If the programmerhas written the program in assembly code, an assembler will be used. If the programmer has
written the program in a high-level language, an interpreter or a compiler will be used.
Aninterpreter converts and runs eachline of code at a time. If it hits an error, it will stop running the code and
notify the user there is an error in the program.
A compiler converts the whole program at once before runningit. It will not run if an error is found and will
produceanerrorreport. An executablefile is created by the compiler.
A compiler operates by going through several stages of compilation. These are lexical analysis, syntax analysis,
code generation and optimisation.
Libraries
Whenwriting a program, a programmermayuselibraries. A library is a pre-programmed routine that can be
used to perform a specific task in the program. If libraries have been used in a program,a linkeror a loader
will be required after the code has been optimised. A static linker brings all the code for the library into the
program asit is compiled. A dynamiclinker loads and linksthe libraries at run time. A loaderis also used thatis
responsible for loading the program into memory.It is often thought that a dynamic linkeris a type of loaderalso.
13
Software development
Building software can be challenging, time consuming and expensive. It often requires a certain approach
depending on the amount of time and fundsavailable. There are several different models that can be followed
when building software: the waterfall model, agile programming, extreme programming, the spiral model and
rapid application development.
Methodologies
The waterfall model is a well-known, but rather outdated model. It consists of several stages of development
that are completed one after the other. These include analysis, design, development, testing, implementation
and maintenance. Agile methodologies are when software is produced through aniterative process. An
example of an agile methodology is extreme programming. This relies on very short development cycles.
The spiral model is more risk-driven. It is also an iterative process that passes through four main stages
repeatedly: determining objectives, identifying and resolving risks, development andtesting, and planning the
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Rapid application developmentrevolves around the useof prototypes. A prototype is produced, feedback is sought
and this then informs the developmentof the next prototype.
Each software development model has benefits and drawbacks. The waterfall model is simple and easy to
managebut requires a lot of time. Agile methodologies can produce software in a muchshortertime than the
waterfall model. The spiral model is very goodfor larger projects that may have a greaterlevel of risk. Rapid
application works effectively for projects that don’t have clear requirementsas it allows them to evolve as the
prototypesarebuilt.
. © Draw a diagram to represent the waterfall model.
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for the company to use. Justify your choice.
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Types of programming language
Programmers can use several different programming paradigms to create computer programs. Each programming
paradigm hasa different approach to how to create the program.
One programming paradigm is procedural programming. This programming paradigm is based around the
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22) Explain what is meant by the procedural programming paradigm.
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There are several alternative programming paradigms. These include declarative, imperative, functional and
object-oriented. Declarative programmingis abouttelling the program whatit should be achieving, whereas
imperative programming should tell the program howto achieveit. Functional programmingis a declarative
approachthatis focused around building a collection of functions. Object-oriented programming focuses on the
developmentof objects rather than actions. It focuses on incorporating both data and processes, rather than
treating them as separate elements.
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creation of subroutines that can be called at any point in the program.
Object-oriented programming
Object-oriented programming involves the use of classes, objects, methods,attributes, inheritance, encapsulation
and polymorphism.
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Inheritance is a fundamental aspect of object-oriented programming. Often, a system will require multiple
classes. This could involve a parent class that contains the information thatis applicable to all objects, then
child classes are created that contain more specific information. On most occasions, a child class will inherit the
attributes and methods from the parent class. This means that if an object is created based on a child class,it will
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programmingthatfall into the definition of polymorphism. One example would be a methodthatis defined in a
parent class but overridden in a child class, dependenton certain circumstances.
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account’ and ‘savings account’. Expand and adapt yourclass diagram to include
the child classes.
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State what this is an example of.
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Assembly language (Little Man Computer)
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One language that computer programsare written in is assembly language. All processors will convert any
computer program to binary to be processed. Assembly language is a low-level computer language that can be
converted very quickly.
A simulation called Little Man Computer can be used to see how the CPU processes assembly code. There are
several versions of the simulation available via the internet. Each instruction in LMC has an opcode and an
operand. The opcodeis the mnemonic that defines that action that takes place, for example LDA, and the operand
is the part that the action is performed on, for example, Num1.
Mnemonic
Instruction
ADD
Add
SUB
Subtract
STA
Store
LDA
Load
BRA
Branch always
BRZ
Branchif zero
BRP
Branchif zero or positive
INP
Input
OUT
Output
HLT
End program
DAT
Data location
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Table 1 The opcodes that can be used in LMC
TENA
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32 Write a program for LMC that will loop five times, outputting a value each time thatis
stored in a location named B. After it has looped five times, it outputs a value stored
in a location named andstops.
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Memory addressing
=
_
When we need to access memory locations in assembly code we can use several different methods. These include
direct, indirect, immediate and indexed addressing.
In direct addressing, the assembly coderefers directly to a location in memory that we wantto put the data. For
example:
INP
STA 5
HLT
The instruction to store the inputdirectly points to addresslocation5.
In indirect addressing, the assembly coderefers indirectly to an address in memory of data that is required.
Therefore, STA 5 would now mean that whatever value is stored in address 5 would be the address ofthe value
that needs loading into the accumulator. For example, if 12 was stored in address 5, then the value stored in
address 12 would be loaded into the accumulator.
In immediate addressing, the operand value is the actual value that we require in the accumulator. Therefore,
In indexed addressing, the index register is used. The value stored in the index register is the address required.
The index register can be incremented to changethe value for the address required.
Exam-style questions
Ç
€) Write an algorithm to explain how datais retrieved from virtual memory.
34 Explain how an interrupt service routine operates.
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STA 5 would now mean that we want 5 in the accumulator.
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State which translator Luke should use. Justify your choice.
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36[ Nancy uses an interpreter to create code for her school project. Explain why Nancy
would use an interpreter rather than a compiler while creating the code.
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€ Luke has a program that he wants to send to his friend Alice. He wants Alice to just
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E Nancy has finished creating the code and now wants to compile it. She has used
libraries when creating her code. Explain how Nancy's code is compiled.
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21
(38) Many companies now prefer agile software development methods rather than the
classic waterfall lifecycle. Discuss why this change has occurred.
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nn ‎‫ ا‬nn nn nn nn nn nm nn nnsses
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DOOR
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)04 Write an assembly code program for a guessing game.
The program must:
= allow the numberto be guessed to be input
allow the numberbeing guessed to be input
allow a userfive tries to guess the number
output the number1 if the numberis guessed correctly and terminate the program
output the number0 if after five tries the numberis not guessed correctly and terminate the
program
Writeyour answer on a separate sheetofpaper.
Exchanging data
Compression
When data is exchanged between different systems we often need to compress it to make the process more
efficient. There are two methods of compression that can be used, lossy and lossless.
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In lossy compression, the size ofthe file is reduced by permanently removing some of the data. The data thatis
targeted for removal is data that is thought to be the least important detail. This will reduce the quality ofthefile,
but possibly not in a way that most people would notice.
In lossless compression, the size ofthe file is reduced by temporarily changing the data it contains, but not
removing any ofit. The original data can be restored whenthefile is decompressed. Two methodsoflossless
compression are run-length encoding and dictionary encoding.
Run-length encoding is used whenrepeating values occur consecutively. These values can be compressed by
recording the numberofrepetitions.
Dictionary encoding is when repeating values are encoded using a dictionary. Each character or wordis given an
index in the dictionary.
pone minimise
| @ state what is meant by compression.
o
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mark
OnO
:
2521317111 100 TS ec pr
6 Identify the two types of compression that can be used.
COn
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marks)
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©) Explain whylossy compressionis not suitable fora textfile.
Em
AO
Ann
(E) Considerthe phrase: 'Every day,in every way, | am getting better and better.
a
marks)
Encode the messageusing run-length encoding.
A
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210111011010111 111111100011111 11 ‎10101010111111111‫[ [ [ [|[زازا‬1# +1 1 01011111111111 ‫لل‬
23
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Encode the messageusing dictionary encoding.
c
Explain which encoding methodis better and why.
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Encryption
Whendata is exchanged betweendifferent systems we often need to encryptit. This meansthatif the data is
stolen, it will be meaningless to the perpetrator. Before data is encrypted it is knownasplain text. Data that has
been encrypted is known as cypher text. A key is used to encryptdata that is a form of encryption algorithm.
There are different types of encryption that can be used: these include symmetric and asymmetric.
In symmetric encryption, a single key is used. The same keyis used to both encrypt and decryptthe data.
In asymmetric encryption, two different keys are used. One key is knownas a public key and the othera private
key. The public key is used to encrypt the data. To decrypt the data, the public key mustbe applied with the
private key.
Hashing
Hashingis like encryption,in that data is effectively encrypted, but data cannotbe directly decrypted in hashing.
It is basically a one-way process. An example of a use for hashing could befor the storage of passwords. A
company may need to store users’ passwordsfor their accounts. The company probably does not wantto
store the actual password string, becauseif it was hacked, it would be very easyfor the hackerto steal all the
passwords. Therefore, a hash function (also knowna hash algorithm) could be applied to the password before
it is stored. This would meanthatall that is stored is the hash version of the password. Whena userenters their
password, the hash function is applied again to see if the outcome matchesthe version stored.
‫ظ‬
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|
|
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© State what is meant by an encryption key.
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A databaseis a collection of data thatis related. A flat-file database has a single table and a relational database
has multiple tables with a relationship linking them together. A primary key is a uniquefield in a database and a
foreign key is a primary key in one table that appears in anothertable to create a link. There are several methods
that can be used to access data in a database. This includes serial and sequential access.
In serial access, each record will be looked at until the record requiredis found.If the record requiredis close to
the top of the table, then accesswill be relatively quick, butif it is near the bottom of a large table, access will be
slow.
In sequential access, a similar process to serial occurs in that each record is lookedat; it is just that the records
have been organised into a certain orderto aid the process. Sequential access can makeuse of an index. For
example, if customers are put into alphabetic order, an index of A, B, C etc. can be used. If a customer has a
namebeginning with D, each index can be lookedat until D is found, then all D records can be lookedat until the
customeris found.
١ © State what is meant bya flat-file database.
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| 02 Explain what a primary key is and whyit is needed.
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D Describe how Mrs Alice Jones would be found using serial access.
marks)
8
Normalisation
A process called normalisation can be used to separate the data, to avoid the issue of data redundancy. Data that
is unnormalised (UNF/ONF) has repeated entries of data and it may also have datathat is not atomic.
The first stage of normalisationis first normal form 1NF. For 1NF, the following rules are applied:
= The table will not have any repeating entries of data, or repeatingfields.
8 All the fields in the database will be atomic.
# Each record in the database will be unique and have a uniqueidentifier.
The second stage of normalisation is second normal form 2NF. For 2NF, the following rules are applied:
= Data must be in INF.
= Any data that is not dependent on the primarykey of a table will be separated into a different table.
Thethird stage of normalisation is third normal form 3NF. For 3NF, the following rules are applied:
= Data must be in 2NF.
m Anyfields that are not directly related to each other are given further separation.
Once a databaseis normalised, relationships can be created betweeneachtable in the database, using the
primary key andlinking it to the foreign key in anothertable.
Rs
Data integrity is a very important issue in a database and measuresthat can be taken to maintain data integrity
are imperative. One way of maintaining data integrity is referential integrity. This is where a processis applied to
stop actions performed on a database creating inconsistent data. The process of normalisation naturally improves
data integrity, because it uses referential integrity.
(E) State what is meant by normalising a database.
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: @) Consider the following database.
‎١
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marks
Artist/Band
Contact details
Booking
date
Venue
Fee
Manager/Agent
PopRUs
poprusQus.com
07777777771
01/01/2019
The Arena,Play St,
London, LN1 1LN
2000
Mandy’s Music
|
Guitar
077777177772
playthatguitar@us.com
02/01/2019
The Hall, Sing St,
3500
Jenna Jackson
‎‫ا‬
Jonesy Jones
jonesyjones@us.com
02/01/2019
The Arena,Play St,
3000
Jenna Jackson
.
The Sing
Songers
singsongers@us.com
07777777774
03/01/2019
The Academy, Guitar St,
Birmingham, B1 1BB
2500
Billy Bob
Up The Charts
upthecharts@us.com
07777777775
03/01/2019
The Hall, Sing St,
Manchester, M1 1MM
2500
StarsRUs
ThrashOut
thrashout@us.com
07777777776
04/01/2019
The Arena,Play St,
London, LN1 1LN
2000
Billy Bob
|Jonesy Jones
jonesyjones@us.com
07777777773
05/01/2019
The Hall, Sing St,
Manchester, M1 1MM
2500
Jenna Jackson
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PopRUs
poprus@us.com
07777777771
05/01/2019
The Academy, Guitar St,
Birmingham, B1 1BB
2500
Mandy's Music
_
Up The Charts
upthecharts@us.com
07777777775
06/01/2019
The Academy, Guitar St,
Birmingham, B1 1BB
3000
StarsRUs
1
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Normalise the database to 1NF.
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b Normalise the database to 2NF.
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Normalise the database to 3NF.
Writeyour answers on a separate sheetofpaper.
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Structured query language (SQL)
To search a database, a language called SQL can be used. There are several SQL commands that you need to be
able to use.
SELECT
Used to say what data will be selected, often the name of a field.
FROM
Used to say where the data will be selected from, often the name ofa table.
WHERE
Used for a condition that needs to be applied.
LIKE
Used to further refine a condition, for example a wildcard.
AND
An operator used with multiple conditions.
OR
An operator used with multiple conditions.
DELETE
Used to remove data.
INSERT
Used to add data.
DROP
Used to remove whole sections of data, for example a table.
JOIN
Used to combine data.
Table 2 SQL commands
These commands can be combined to create an SQL search.
An example of an SQL search would be:
SELECT “CustomerForename”,
“CustomerSurname”
FROM “tblCustomers” WHERE
“MailingList” = “Yes” AND “NewsLetterSent” = “No”
This search is designed to return the namesofall customers whoare signed upto the mailing list but haven’t
been sent a newsletter.
2/
ACID rules
When any additions or amends are made to a database, thisis called a transaction. To protect the integrity of the
data in a database, transactions should conform to certain rules. These rules should uphold the ACID properties:
atomicity, consistency, isolation and durability.
Networks
Many organisations and individuals make use of a network. There are several different types of network, these
include private networks,virtual networks, LANs and WANs. Networks can have manydifferent models: two of
these are client-server and peer-to-peer.
A client-server network has two main types of computer, a client and a server. The serveris the centre of the
network and providesservices and data for the clients on the network.
A peer-to-peer network doesnot have a central system to manage the network. The managementof the networkis
the responsibility of each individual peer.
Each network can also havea different structure, including bus, ring, star and mesh.
Protocols
For communicationto be effective using a network,there are several protocols and standards that need to be
upheld. Protocols are rules that govern how a networkoperates. They makeit possible for manydifferent devices
to communicate using a network. Protocols are normally made upof layers. This is an inbuilt form of abstraction.
Each layerin the protocol hasa different responsibility. One protocol that is commonly used is the TCP/IP protocol.
This is used in communication across the internet. The TCP/IP protocol has fourlayers.
Layer
Responsibility
Application layer
To collect and distribute data, making sure it suitable for transmission.
Transportlayer
To establish and terminate connections between devices. To perform error detection
Internet layer
To establish a route from the sender to the receiver.
Network/Link layer
To makes sure the transmission media is in place.
and establish the speed datais sent.
Table 3 TCP/IP layers
Someprotocols and systems can have as manyas sevenlayers, for example the OSI model.
Data can be exchanged across a network using packet switch or circuit switching. When we send data across a
network, we divide it into packets. In circuit switching, packets are sent across a set route. In packet switching,
packets are sent across any routethatis available.
0 State what is meant by a network.
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20) Draw a diagram to represent how datais sent in a packet-switching network.
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Network security
One of the issues with networksis that they are often subjected to manydifferent threats. These include
malware, brute-force attacks, denial-of-service attacks and theft of data. There are several ways a network
can beprotected, such as a firewall or a proxy server. Data being transmitted across the network can also be
protected through encryption. This would make the data meaninglessif it was stolen. Each methodof protection
cannot guarantee an attack will not occur, but it can makethe possibility far more difficult.
Hardware
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A network can contain several different components. These include a network interface card, a router, a switch,
wireless access points, transmission media and possibly a domain nameserver.
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22 Describe the role of a router in a network.
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_ @) Describe the role of a domain name serverin the internet.
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The internet
Web authoring tools
HTMLis the most basic language used to author web pages. There are several HTML tags you need to be able to
use. CSSis a formatting method that is used to create a consistent style for web pages. There are a number of CSS
properties that you need to be able to use.
JavaScript is a programming language that is used to add interactivity to web pages. You need to be able to create
inputs and outputs using JavaScript commands.
; 24 Complete the table to describe the use of each of the HTML tagslisted.
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<link>
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<p>
<li>
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<ol>
<ul>
<script>
ْ 125) State what a ‘#' is used for in CSS.
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that has a width of 5 pixels, and all text must be Arial, point size 16 and black.
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= Information boxes must have a background colourof pale blue and a black border
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Search engines
Search engines search the world wide web for web pages that match the keywords entered into the search bar.
To do this they use a complex search algorithm. Search engines build up large indexes of web pages to make the
searching process moreefficient. Organisations add meta data to the headerof their website. This meta data
contains keywords that the search engine can easily find.
It is important that a search engine can quickly provide the user with a list of useful web pages that match
their search criteria. One of the most successful tools in providing this service is the Pagerank algorithm. This
algorithm looks at more than the content of the web page. It also assesses how many other web pages are linked
to a web page and givesit a higher ranking based onthis.
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The processing of data that is exchanged overthe internet can be carried out in two ways, at either the client side
or the server side. When data is processed at the client side, it reduces the load on the server. However, when data
is processed at the server side, data can be kept more secure.
_ @) State whatis meantby a search engine index.
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€{) Describe how asymmetric encryptionis used to send data securely.
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ED Consider the following database.
The table is called Customer.
Cust no
Title
Forename
Surname
House no
Street
1001
Mr
Benny
Jones
1
New Street
1002
Mrs
Emily
Rose
1
1003
Miss
Victoria
Bloom
2
1004
Mr
Luke
1005
Mrs
1006
Mr
a
Town
Postcode
Order no
New
NST INT
001
Old Street
Old Town
OS1 10S
002
New Street
New
Town
NST INT
003
Miles
Old Street
Old Town
|OS1 10S
|004
Alice
Jones
New Street
New
NST INT
005
John
Smith
Old Town
OS1 10S
006
3
Old Street
Town
Town
Write an SQL statement that would return the forenameof all customers wholive in Old
Town.
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Pr ‎‫ ا ا ا ا ا ا ا ا ل ل ل‬rr rr rs sr rr rr rr rr ‎‫ ا ا ا ا ا ا ا ا ا‬rr ‎‫ ل ل ا ا ا ا ل ا ا ل‬rr
b
Write an SQL statement that would return the full names and titles of all customers wholive
in New Town.
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SRE EE‫ممممم ةنم ء من ةر ور ريج وترم رن مر رم برج مر وك و ومو ووم ه مرل م ء رو مومه نمم مره وكيا ل لمم وو مرو هموعنو فلم ممم م في م مورو مر مو مر رو م ررم مر او ووم م رم عبر اماع اام اماما ااا اا ااا ااا اا ااا عاو اا ‏‬
©
Write an SQL statement that would return the titles and surnames of all customers who live
in Old Town and have an order number greater than 003.
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rr rs rr rs a rr sr rr ss rr rr
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(32) Describe how a firewall can be used to improve the security of a network.
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€) Give two benefits and one drawback of using a network.
EZ) Explain the role of the transport layer in the TCP/IP protocol.
€) State two reasons why a company would chooseto haveclient-side processing.
35
Data types, data structures and
Boolean algebra
Data types
Data can be of many different types. These include string, character, integer, real and Boolean. We need to assign a
suitable data type to any data westore to make sure that we can useit in the most efficient way.
Representing positive integers
All data needs to be converted to binary in order to be processed by a computer system. It is important to know
how to represent a positive integer as binary.
It is useful to be able to convert positive integers tohexadecimal. Hexadecimalis often used instead of binary as
it is a shorter method of representation and can be easier to read. To convert a positive integer to hexadecimal, a
simple method is to divide the numberby 16, this will be the number of the unit 16 needed, and then the remainder
is the number of 1s needed.
In hexadecimal notation,numbers 1 to 9 are the same, but 10 to 15 are represented by the characters A to F.
Therefore, 178 in hexadecimal notation is B2. If 16 of the unit 16 need to be used, then the next unit is required,
which is 256.
© Convert the denary value 101 to binary.
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nn nn nn nn nn nn nn nn nn nn nn nn nn nn nn nn nn nn nn nn nn nn nn nn sm nn nn nn nn nn ne non ns nn son nn nn nn nn nn nn nn nm mn nn nn nn nn nn nn nn ns nn mn nn nn nm nn nm nn nn mn mn nn nn ns nn nn mn nn nn nn nn nn nn nn nn nm nn nn nn nn nn nn mn n nm nn msn msn nm sen nnnnnnmnsess
Representing negative integers in binary
There are two waysto represent negative integers in binary, these are sign and magnitude and two’s complement.
For sign and magnitude,this is simply using a bit to signify if the numberis positive or negative. The bit is placed
at the start of the binary number. The namegivento this bit is the mostsignificant bit (MSB). If the numberis
negative, this bit will be 1. If it is positive, this bit will be 0.
In two’s complement the MSBis changed to be a negative number. For example, 128 becomes -128. Therefore, we
start with a value of -128 and addto this value to represent our negative number. Two's complement is the method
used by most computers to represent negative numbers. Another way we can find the two’s complementof a
number is by taking its positive binary values,flipping them, then adding1.
it
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Adding in binary
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To add two binary numbersthere are four rules to remember:
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1+ 1+ 1 = 11 (the binary valuefor 3)
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010101 10
we get the binary value 01010110.
We must carry numbers just like we do in normal addition of numbers. The small numbers underneath are the
numbersthat have been carried. We can add two’s complement binary numbers using the same method. If we end
up with an extra carry at the end,this is called an overflow.
@ Add together the binary values 00011100 and 10000001.
ama
@ Add togetherthe binary values 10010101 and 11001001.
marks
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Subtracting in binary
To subtract binary numbers, we use the normal rules of subtraction, but with an additional extra rule. When we
borrow from the next column, we place a value of 2 as the carry. This is because we have borrowed two lots of that
unit. For example, if we borrow from the ‘8’ unit column, weplace 2 in the ‘4’ unit column as we have borrowed
two lots of 4, hence 8. If we cannot borrow from the next column, we have to go to the columnafter and borrow
from thatfirst.
3/
For example:
221
SARA 2
0011420 0 00011110
00011010
© Subtract the two binary values 11001100 and 01010101.
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Subtracting using two’s complement numbers
To subtract using two's complement there are several stages that we need to go through. For example,let's take
the calculation 48 - 22:
We convertthefirst value to binary: 48 as binary is 00110000.
Weconvert the second valueto the two’s complement binary: 22 as binary is 00010110. The two’s complementof
this is 11101010.
Wethen add the two values:
00110000
1110101 0+
111
00011010
We discard the last carry, so we are left with the value 00011010, which is the correct denary value of26.
0 Subtract the two binary values 11001100 and 01010101 using two's complement.
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Representing real numbers in binary
So far, we have only been lookingat representing integer values in binary. We also need to know how to represent
real values in binary. Real numbers in binary have two parts to them, the mantissa and the exponent. The
mantissa is a value that will have a floating point and the exponentis the numberof places the floating point has
‘floated’ to the left. The floating point is placed just after the MSB.
For example: 111101111 110 has a mantissa of 1.11101111 and an exponentof110.
This meansthat the floating point has been movedsix placesto theleft.
If we movethefloating point back six places to the right, we have 1111011.11.
If we convert the valuesto theleft of the floating point, we get 123.
The values after the floating point have fractional values starting with Y. After the floating point there are the
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values Y. and Ys. These values are added together to make % or .75.
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This meansthat the real number represented by the mantissa and exponentis 123.75.
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We can also normalise real values to make sure that we are able to store the largest value possible with the bit
allocation that we have.
©.
| © Show how the value 101.25is represented as a floating point number with a 6-bit
[
exponent and a 10-bit mantissa.
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= It has a 10-bit mantissa and a 6-bit exponent.
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Bitwise manipulation of binary values
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We also need to know how to perform bitwise manipulation and use masks on binary values.
In bitwise manipulation, binary values are shifted to the left or to the right. Any empty spaces after the shift are
filled with zeros.
Each bit shift to the left is like multiplying the numberby two. Each bit shift to the right is like dividing the number
by 2.
We can also use masks with our binary values to perform logical operations.
If we take the binary value 10101010 and the mask 11001100, each operation would give us:
AND
1
0
1
0
1
0
1
1
0
0
1
1
1
0
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1
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0
XOR
1
1
0
1
1
0
0
1
0
We can use these logical operations to check for different patterns in binary values.
39
Ea o
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@ Perform a bitwise left shift of three places on the binary value 01100001.
ON
0 Perform a bitwise right shift of four places on the binary value 11111101.
nn nn nn nn nn nn nn nn men nn mn ne nn nn en mn sn nn nn nn nn nan en nn nn nn nn nement nn nn men nn nn nn en mn mn nn nn nn nn nn nn nm nn nn nn EE REE EEE EERE EE EE REE HEHEHE HEE EROS ERE EE EEE EERE EERE EES EE EEE HEHE SEER EEE EOD
® Perform an AND logical operation on the binary value 11011001 with the
mask 00010111.
Representing text
As all data needsto be converted to binary to be processed by the computer, text also needs to be converted. Text
is converted to binary using a character set. Two commoncharacter sets are ASCII and UNICODE. In a character
set, each letter has an equivalent binary value, for example the binaryvaluefor the capital letter A in the ASCII
characterset is 01000001.
Data structures
Arrays
A one-dimensional array allows us to store onetype of data, e.g. a set of test scores. For example:
12
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| 56
| 64
| 27
| 43
| 12
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96|
Arrays normally start at an index of 0, so index[3] stored number64.
A two-dimensional array allowsusto store two different types of data, e.g. student’s name andthreetest scores.
For example:
Benny
11
13
47
Billy
13
17
33
Boris
45
33
55
Jane
9
32
44
Joanne
54
55
39
Jenna
9
48
31
A two-dimensional array is indexed on both the x and y co-ordinates. Index[0,4] stores Joanne and [2,2] stores 33.
A three-dimensional array allows us to store three different type of data, e.g. student's name, three test scores and
two resit scores for each test. Imagine the table above as a three-dimensional shape with two entries behind each
test score for the resit values.
20) Define an array in pseudocode that would store 10 students' names andsix test scores
for each student.
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(3) Define an array in pseudocode that would store 30 students’ names,five test scores
and three resit scores for each test.
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Records, lists and tuples
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Lists are like a one-dimensionalarray, but with somedifferences. Lists are a dynamicstructure, they are mutable
and slower to access.
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Records and tuples are practically the same thing. The main differenceis that in tuples just the value is stored; in
4
records, a variable name for each valueis stored also. They are a collection of data that is grouped together. Once
they are created they are immutable. You could imagine them asbeinglike a row in a database.
| 22 ROR BSED ARETE RS IE AREABI SEES ANUNREDARAGON a AEW USIE
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Stacks and queues
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Data can be stored in several different structures. Two structures that can be used are stacks and queues.
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A stack can be described as a Last In First Out (LIFO) structure. Data is added to the top of the stack and removed
from the top of the stack.
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A queue can be describedasa First In First Out (FIFO) structure. Data is added to the end of the queue but removed
from the front of the queue. Queues can becircular structures.
| 24 The following data is stored in a stack: 25, 36, 75, 33, 29, 40.
:
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The value 25 is the bottom of the stack. Show what the stack would look like after
the following operations have been carried out.
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POP
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PUSH 13
POP
nn nn nn nn nn nn nn nn nn nm nn nn nn nn nn nn nn nn nn nn nn ne ns nn nn non mn nn nn sn nn nn nn mens nn nn ns nn nn nn nn nn nn nn nn ne nn n nn nn ns nn mme nn nn nn sn nn nn nn nes nn n nes nn nn nn nn sun msn sms sense ‎‫ال ع ع ع ا ا ا ا‬
)1( Thefollowing data is stored in a circular queue: 25, 36, 75, 33,29, 40.
The value 33 is the start of the queue and the value 75is the end of the queue. Show
what the queue would looklike after the following operations have been carried out.
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41
Linked lists, graphs, binary trees and hash tables
A linkedlist is an ordered set of data, each of which contains a pointer to the next item of data (and sometimes
the preceding item of data). Linked lists have two advantagesoveranarray in that they are dynamic anditis
easier to add and removedata. Data is added to a linked list using the free space pointer. The pointer from the
preceding data item will need to be updated to point to the newly added item. To remove an item from a linked
list, the pointer from the preceding item to the one being removed, is changedto point to the new nextitem of
data. A traverse of a linkedlist will start at the beginning and look at each item in turn until the item required is
found.
A graphis a collection of data nodes and the connections between them. There are two approachesto traversing
a graph andthese are depth-first and breadth-first.
A binary tree is made up of parent and child nodes. A parent node can have two child nodes,a left and a right
child.
Hashtables are used to allow direct access to records than are stored in an array. An address of a record in the
array is calculated from the key value of a record. This processis called hashing.
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| y The following data is stored as a linkedlist:
‎‫ظ‬
Option A, Option B, Option C, Option D
Option B will no longer be available, so it needs to be removed from thelist.
Explain how option B is removed from the linked list.
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128) Explain the difference between traversing a graph using depth-first and breadth-first
traversal.
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Boolean algebra
Karnaugh maps
Boolean algebra is a complex topic. You need to be able to simplify Boolean expressions using a Karnaugh map. In
order to simplify a Boolean expression using a Karnaugh map the expression needs to be in sum-of-products form.
There are several rules that need to be applied when creating a Karnaugh map. Groups:
‫ "ا‬can only be created in multiples of 2
Ñ cannot contain cells with 0/blank
m cannotbe diagonal
Ñ should be as large as possible‫‏‬
Ñ can overlap‫‏‬
# can ‘wrap around’ the map‫‏‬
There are several stages that you can follow to create a Karnaugh map:
y
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Map each term in the Boolean expression with a 1 (or a dot).
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Simplification rules
Boolean expressions can also be simplified using the rules of simplification. Thefirst rules that you need to
understand are often referred to as the rules of double negation, or identity.
AAA=A
AVA=A
- (- À) = À
AAA=0
(False)
AvV-=A=1
(True)
Law
AND
OR
Commutative
|AAB=BaA
AVB=BvA
Associate
(AAB)AC=Aa(BAC)
(Av B)vC=Av(BvC)
Distributive
AA(BVC)=AABVAAC
Av(BAC)=AVBAAVC
Table 4 Further rules of simplification
You need to be able to apply these rules to simplify a Boolean expression.
Thereis a final set of rules that you needto be able to apply. These are called De Morgan’s rules. The rules
of De Morgan’s are:
=(AVB)=-AA-B
=(AAB)=-AV-B
43
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Logic gates
Logic gates are the foundation of logic processes in a computer. You need to understand the logic of several logic
gates, including how to create truth tables for them. Thelogic gates that you need to understand are AND, OR,
NOT, NAND, NOR and XOR. You need to be able to combine these logic gates to create a logic diagram.
Adder circuits
You also need to understand the logic of half and full adders and flip flops.
A fundamental operation in computersis the addition of binary values. A simple circuit that can be used for
binary addition is a half adder.
The half addercircuit takes in two inputs and outputs a sum bit and a carrybit.
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0
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The logic of a half adder can be shownin a truth table as:
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A full adder circuit has three inputs, including the previouscarry bit.
The logic of a full adder can be shownin a truth table as:
A
|B
|Carryin
Sum
|Carry out
0
10
|0
0
0
0
10
|1
1
0
0
|1
[0
1
0
0
11
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0
1
1
[0
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1
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10
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Flip-flop circuits
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The logic of flip-flop circuit can be shownin a truth
table as:
‎‫ده‬
A flip-flop circuit is one of the most fundamentallogic
circuits in digital technology. A simple flip-flop circuit
would be:
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6 Using the laws of simplification, simplify the following Boolean expression.
Exam-style questions
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mask 00010111.
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marks)
ELM, APPLE, OAK, BEECH, BIRCH,FIR, MAPLE, ASH, PINE, BAY
Writeyour answer on a separate sheet ofpaper.
69 Simplify the following Boolean expression using a Karnaugh map.
BaCA=AvVBA=CrgAvAr-BrCvaBACAHAvVAA-BAC
Writeyour answer on a separate sheet ofpaper.
€) Using the lawsofsimplification, simplify the following Boolean expression.
B À - B À (A 4 B) v (AAC)
nn
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45
Computer law and ethical, moral
and social issues
Computer law
There are four main legislative Acts that you need to understand:
= Data Protection Act (1998)
#8 Copyright Design andPatents Act (1988)
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Computer Misuse Act (1990)
Regulation of Investigatory Powers Act (2000)
Each Act regulates a different element of the use of data or technology. Computercrimeis an increasing issue and
governments andlegislation are struggling to keep up with advancements in computercrime. A relatively new
law that also regulates the use of data is the General Data Protection Regulation (GDPR). This is an EU law that
regulates the processing of personal data within the EU. It was designed to make the regulations muchclearerfor
both people and businesses.
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Ethical, moral and social issues
The developmentof technology and how weuseit has brought about several moral andethical issues. The
introduction of computers into society has created issues in various areasof society. The introduction of computers
in the workplace has brought about a fear of job loss and also unease about computers performing certain tasks.
The use of computers for automated decision making can also create unease dueto the reliance only on logic.
One of the more recent developmentsat the forefront of moral andethical issues is the developmentofartificial
intelligence. There is increasing concern expressed that allowing computers to develop something close to a
conscience can be a large risk to manage.
Anotherpressing concernis the effect of computers on the environment. Computers can be made from sometoxic
materials that need to be handled with great care. If these materials are not disposed of correctly, they can seep
into our soil and affect our food systems.
There has beena lot of debate aboutthe accessibility of material using the internet. Some people believe that there
should be much more censorship in place, while others thinkthat is a violation of humanrights. Some countries
havefar greater levels of censorship than others. Computers are increasingly used to monitor our behaviour.
Again, some peoplethinkthis is a necessity to keep society safe, but others believe it creates a nanny state and isa
violation of humanrights.
Computersare used to mine vast amountsof data that is analysed by organisations. The analysing of our
information in this wayis also seen as controversial. People worry about the amountof data that organisations
hold about us and the dangerand security issues that surroundthis.
Anincreasing problem with technologyis the issue of piracy. Some people believe the entertainmentindustry
charges too muchfor the products they create. This has led to some people pirating copies of the product.
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Exam-style questions
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O Discuss the implications of the Data Protection Act on a company gathering data for
marketing and selling it to global organisations.
47
Consider the following statement:
Some people believe that there is too much censorship of content available on
the internet, believing this to be a violation of human rights. Others believe that
there is not enough censorship and more should be putin place.
Discuss the merits of this statement.
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