Example 1 - Ask Pak Chairul

Unit 1: Introduction to computer systems
A computer is an electronic device, operating under the control of instructions stored in its own memory
Definition and examples of:
 Input device is any hardware component that allows users to enter data and instructions into a computer.
 Output device is any type of hardware component that conveys information to one or more people.
 Storage device is a device that holds data, instructions, and information for future use.
Input devices:
 OCR (Optical character recognition): reading characters or text from ordinary documents.
 OMR (Optical mark recognition): reading hand-drawn mark such as small circles or rectangles in a multiple
choice answer-form.
 MICR (Magnetic ink character recognition): reading text printed with magnetised ink; like checque books.
 Magnetic stripe reader: reading the magnetic stripe at the back of cards.
 Biometric scanner: authenticating a person’s identity by verifying a personal characteristic; such as fingerprint, retina, palm-print, face-recognition, etc.
 RFID (Radio frequency Identification): uses radio signals to communicate with a tag placed in or attached to
an object; such as books locator, wardrobe locator, airline baggage locator, etc.
Output devices:
 A nonimpact printer forms characters and graphics on a piece of paper without actually striking the paper.
Examples: ink-jet printer, laser printer, plotters, photo-printers.
 Impact printers form characters and graphics on a piece of paper by striking a mechanism against an inked
ribbon that physically contacts the paper.  Good to be used for printing documents on a carbonised paper.
Examples: dot-matrix printer and line printer.
 A storage medium is the physical material on which a computer keeps data, instructions, and information.
Examples: CD-R, DVD-R, memory card.
 A storage device is the device to read data stored in the storage medium. E.g. CD-drive, DVD drive,
memory card reader.
 The difference between storage medium and storage devices.
 Access time measures the amount of time it takes a storage device to locate an item on a storage medium.
 Flash memory chips are a type of solid state media and contain no moving parts.
 Solid state drives (SSDs) have several advantages over magnetic hard disks: faster access time, faster
transfer rates, less heat, consume less power, last longer.
 Cloud storage is an Internet service that provides storage to computer users.
 A DVD-ROM is a high-capacity optical disc on which users can read but not write or erase.
 A DVD-R is a multisession optical disc on which users can write, but not erase.
 DVD-RW, DVD+RW, and DVD+RAM are high-capacity rewritable DVD formats.
 A Blu-ray Disc-ROM (BD-ROM) has a storage capacity of 100 GB
 Tape is a magnetically coated ribbon of plastic capable of storing large amounts of data and information
 A tape drive reads and writes data and information on a tape
 A magnetic stripe card contains a magnetic stripe that stores information
 A smart card stores data on a thin microprocessor embedded in the card
 Microfilm and microfiche store microscopic images of documents on a roll or sheet film
Sensors: part of input devices that can read physical quantities; such as:
 Humidity
 Temperature
 Light intensity
 Speed
 Pressure
 Motion
Describe how the sensors and the microprocessors are used to maintain the correct conditions of temperature and
oxygen in the fish tank.
Unit 2: Numbers, processors and operating systems
Binary has two numerical notations: 0 and 1.
That is why we also call binary numbers with base 2 numeric system.
Decimal has 10 variants of numerical notations: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
That is why we call it base 10 numeric system.
Example #1
Convert BINARY 11101 to DECIMAL
=1*(2^4) + 1*(2^3) + 1*(2^2) + 0*(2^1) + 1*(2^0)
1*(16) + 1*(8) + 1*(4) + 0*(2) + 1*(1)
= 16+8+4+0+1
= 29
Example #2
Convert BINARY 1010 to DECIMAL
Let's convert 835 to binary.
The most significant bit is the left number in the answer and the least significant bit is on the right
end giving us an answer of: 11010000112
Hexadecimal has 16 variants of numerical notations: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F. That is why
we call it base 16 numeric system.
Decimal has 10 variants of numerical notations: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
That is why we call it base 10 numeric system.
10 11 12 13 14 15
Example #1
Convert the number 256 DECIMAL to HEXADECIMAL
256 / 16
16 / 16
1 / 16
Example #2
Convert the number 921 DECIMAL to HEXADECIMAL
921 / 16
57 / 16
3 / 16
Example #3
Convert the number 188 DECIMAL to HEXADECIMAL
(in HEX)
188 / 16
C (12 decimal)
11 / 16
B (11 decimal)
Note: Here, the answer would not be 1112, but BC. Remember to write down the remainder in hex,
not decimal.
Example #1
Convert the number 589 HEXADECIMAL to DECIMAL
9 x (16^0)
8 x (16^1)
5 x (16^2)
If you want to be a speed counter, it's beneficial to memorize the values of the smaller power of 16s,
such as in this table
16^1 = 16
16^2 = 16x16
16^3 = 16x16x16
16^4 = 16x16x16x16
Example #2
Convert the number 1531 HEXADECIMAL to DECIMAL
(This time, let's use the table of the power-of-16s above.)
3 x 16
5 x 256
1 x 4096
Example #3
Convert the number FA8 HEXADECIMAL to DECIMAL
A x 16 (remember that hex A=decimal 10)
F x 256 (remember that hex F=decimal 15)
Example #4
Convert the number 8F HEXADECIMAL to DECIMAL
8 x 16
One bit of Hexadecimal represents 4 bits Binary number.
This also means:
Four bits of Binary number is represented in One bit Hexadecimal.
Convert each 4 binary digits to hexadecimal digit according to this table:
Example 1
Convert (01001110)2 to hex:
(0100)2 = (4)16
(1110)2 = (E)16
(01001110)2 = (4E)16
Example 2
Convert (0100101000000001)2 to hex:
(0100)2 = (4)16
(1010)2 = (A)16
(0000)2 = (0)16
(0001)2 = (1)16
(0100101000000001)2 = (4A01)16
One bit of Hexadecimal represents 4 bits Binary number.
This also means:
Four bits of Binary number is represented in One bit Hexadecimal.
Convert each hexadecimal digit to 4 binary digits according to this table:
Example 1
Convert (4E)16 to binary:
(4)16 = (0100)2
(E)16 = (1110)2
(4E)16 = (01001110)2
Example 2
Convert (4A01)16 to binary:
(4)16 = (0100)2
(A)16 = (1010)2
(0)16 = (0000)2
(1)16 = (0001)2
(4A01)16 = (0100101000000001)2
The microprocessor is sometimes referred to as the
'brain' of the personal computer, and is responsible for
the processing of the instructions which make up
computer software.
CPU Structure consists of five parts, which are:
Arithmetic & Logic Unit (ALU)
The part of the central processing unit that deals with
operations such as addition, subtraction, and
multiplication of integers and Boolean operations. It
receives control signals from the control unit telling it
to carry out these operations.
The simplified model of the central
Control Unit (CU)
This controls the movement of instructions in and out processing unit. Click on an area for
of the processor, and also controls the operation of the more details.
ALU. It consists of a decoder, control logic circuits,
and a clock to ensure everything happens at the correct
time. It is also responsible for performing the
instruction execution cycle. More on the control unit
can be discovered by clicking the title above.
Register Array
This is a small amount of internal memory that is used for the quick storage and retrieval of data
and instructions. All processors include some common registers used for specific functions,
namely the program counter, instruction register, accumulator, memory address register and stack
System Bus
This is comprised of the control bus, data bus and address bus. It is used for connections between
the processor, memory and peripherals, and transferal of data between the various parts.
The memory is not an actual part of the CPU itself, and is instead housed elsewhere on the
motherboard. However, it is here that the program being executed is stored, and as such is a
crucial part of the overall structure involved in program execution.
Following on from looking at the structure and architecture of the central processing unit itself,
we shall now look at how the CPU is used to execute programs and make the computer as a whole
run smoothly and efficiently. To do this, we must take a step back from concentrating solely on
the processor, and look at the complete computer unit.
A flow diagram illustrating the flow of data within the PC during program
execution and the saving of data. Further explanation can be found below.
When software is installed onto a modern day personal computer (most commonly from a CDROM, though other media or downloading from the internet is also common), code comprising
the program and any associated files is stored on the hard drive. This code comprises of a series of
instructions for performing designated tasks, and data associated with these instructions. The code
remains there until the user chooses to execute the program in question, on which point sections
of the code are loaded into the computers memory.
The CPU then executes the program from memory, processing each instruction in turn. Of course,
in order to execute the instructions, it is necessary for the CPU to understand what the instruction
is telling it to do. Therefore, recognition for instructions that could be encountered needs to be
programmed into the processor. The instructions that can be recognized by a processor are
referred to as an 'instruction set', and are described in greater detail on the next page of the
Once the instruction has been recognized, and the actions that should be carried out are decided
upon, the actions are then performed before the CPU proceeds on to the next instruction in
memory. This process is called the 'instruction execution cycle', and is also covered later on in this
tutorial. Results can then be stored back in the memory, and later saved to the hard drive and
possibly backed up onto removal media or in seperate locations. This is the same flow of
information as when a program is executed only in reverse, as illustrated in the diagram above.
On the next page of this tutorial is a more in-depth look at instruction sets. Click the next arrow
below to proceed.
Once a program is in memory it has to be executed. To do this, each instruction must be looked at,
decoded and acted upon in turn until the program is completed. This is achieved by the use of
what is termed the 'instruction execution cycle', which is the cycle by which each instruction in
turn is processed. However, to ensure that the execution proceeds smoothly, it is is also necessary
to synchronise the activities of the processor.
To keep the events synchronised, the clock located within the CPU control unit is used. This
produces regular pulses on the system bus at a specific frequency, so that each pulse is an equal
time following the last. This clock pulse frequency is linked to the clock speed of the processor the higher the clock speed, the shorter the time between pulses. Actions only occur when a pulse
is detected, so that commands can be kept in time with each other across the whole computer unit.
The instruction execution cycle can be clearly divided into three different parts, which will now
be looked at in more detail. For more on each part of the cycle click the relevant heading, or use
the next arrow as before to proceed though each stage in order.
Fetch Cycle
The fetch cycle takes the address required from memory, stores it in the instruction register, and
moves the program counter on one so that it points to the next instruction.
Decode Cycle
Here, the control unit checks the instruction that is now stored within the instruction register. It
determines which opcode and addressing mode have been used, and as such what actions need to
be carried out in order to execute the instruction in question.
Execute Cycle
The actual actions which occur during the execute cycle of an instruction depend on both the
instruction itself, and the addressing mode specified to be used to access the data that may be
required. However, four main groups of actions do exist, which are discussed in full later on.
Once a program is in memory it has to be executed.
To do this, each instruction must be looked at,
Diagram showing the basics of the
instruction execution cycle. Each
instruction is fetched from memory,
decoded, and then executed.
Von Neumann architecture and the fetch-execute cycle
the types of question that could be asked here is vital since it is important to go into the required
depth in these two subjects
the following notes show the kind of material teachers need to develop to teach this subject
to the required level:
The following diagram shows a typical computer system that uses Von Neumann
The main components are:
The computer memory is made up of partitions (much like a set of
drawers). Each “drawer” consists of an address and its contents.
The example on the right uses 4 bits for each address and the
contents are made up of 1 byte (8 bits). In reality, the address and
its contents are usually much larger than this!!
The address will uniquely identify every location in the memory
(much like the address used to uniquely identify the location of a
house in a particular city) and the contents will be the binary value
stored in each location.
The figure also shows that the memory is made up of items
known as the MAR (Memory Address Register) and the MDR (Memory Data Register).
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NOTE: an additional register, called the memory buffer register (MBR) is also often referred to in
computer architecture. This is a two-way register that temporarily holds data fetched from memory
or data waiting to be stored in memory (see fetch – execute cycle later).
Processing Unit
The processing unit is made up of the arithmetic and logic unit (ALU) and registers. The ALU
allows arithmetic (e.g. add, subtract, etc.) and logic (e.g. AND, OR, NOT, etc.) operations to
be carried out. Registers are temporary storage areas and also contain the results from the ALU.
Input/Output devices
Input devices convert external data into a form the computer can understand and can then process (e.g.
keyboards and microphones). Output devices show the results of computer processing in a human
readable form (e.g. printers and monitors).
Control Unit
The control unit controls the operation of the memory, processor and input/output devices. It contains
the current instruction register (CIR) and the program counter (PC). The CIR will contain the
current instruction during processing. The PC contains the address of the next instruction to be
Basically, the control unit reads an instruction from memory (the address of where the instruction is
found is stored in the PC) and then interprets this instruction, generating signals to tell the other
components in the computer what to do.
Fetch – Execute Cycle
In the Fetch – Execute Cycle the next instruction is fetched from the memory address currently stored
in the Program counter (PC) and is then stored in the current instruction register (CIR). The PC is then
incremented so that the next instruction can be acted upon.
The decoder then interprets this instruction in the next part of the cycle:
The control unit (CU) passes the decoded information as a set of control signals to the appropriate
components within the computer. This allows all necessary actions to be carried out.
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Role of Registers and buses in the fetch-execute cycle
For completeness, the following lists the actual stages that take place during the fetch – execute cycle
showing the role of all the registers and buses in the process (the first 5 boxes are the fetch cycle and the
last 2 boxes the execute cycle):
the PC contains the address of the next instruction to be
the address contained in the PC is copied to MAR via
address bus
the instruction is then copied from the memory location
contained in MAR and is placed in MBR
the entire instruction is then copied from MBR and
placed in CIR
the value in the PC is then incremented so that it points to
the next instruction to be fetched
the address part of the instruction is placed in the MAR
the instruction is finally decoded and then executed
Please also study:
Unit 3: Data communications and networking
Data transmission between a processor and its peripherals, and between computers in a network, is a
central element in everyday life; the internet has become an unconscious way
of life for many people today. This unit looks at the principles underpinning data transmission in these
Part 1 Serial and parallel data transmission
Show an understanding of what is meant by transmission of data
When data are transmitted from one computer to another they travel along some medium (copper
wire, optical fibre, as radio waves, infra-red) in the form of bits. For example, when the data are
transmitted using wires they are transmitted in the form of voltage changes. The sender will generate
one voltage to represent 1 and a different voltage to represent 0. The sender has a clock and it
transmits bits at regular intervals. At any point in time there will be a number of bits being carried
along the wire so the voltage may be depicted as follows:
Baud Rate
The rate that voltage changes is called the baud. In the simple case described above, if the voltage
changes 10 times every second the baud is said to be 10.
Bit Rate
The bit rate is the term given to the rate that bits are transmitted. In the simple case described
above the bit rate is the same as the baud. If we could generate four voltages, instead of two, we
could use each change in signal to represent two bits.
When a signal is transmitted along a wire (or any other medium) it is reluctant to travel as a square
wave. Waves are naturally in the form of sine waves
All media are capable of transmitting a set of waves that have a range of frequencies. The frequency
of the wave is the rate at which the wave repeats itself. The range of frequencies that a medium can
transmit is known as its bandwidth. The wider the bandwidth, the more
data that can be transmitted. An optical fibre has a very high bandwidth so it can transmit a very
large amount of data. A normal telephone wire has a very low bandwidth so it is not possible to
transmit many data.
Distinguish between serial and parallel data transmission
Serial transmission of Data
Data needs to be transmitted between devices in a computer system. The easy way is by using a single
wire that links the two devices. Data are transmitted down the wire in the form of bits, so a byte that
represents a single character is transmitted as eight bits in sequence, one signal for each bit.
The diagram shows the data byte 01101101 in the process of being transmitted from Device
1 to Device 2. As there is only one wire, only one bit can be transmitted at any time. This is
known as serial transmission of data.
Parallel transmission of Data
If the devices are connected by more than one wire, then more bits can be sent simultaneously. A
sensible number of wires would be eight, because then a whole byte can be sent at the same time.
This type of data transfer is called parallel data transmission.
Show understanding of the reasons for choosing serial or parallel data
Serial transmission of Data
Serial transmission has the advantage of being simple and reliable because the next bit is not
transmitted until the current one has been received. However, because only one bit can be transmitted
at a time, the transmission is slow. All peripheral devices that connect through a Universal Serial Bus
(USB) use serial data transmission.
Parallel transmission of Data
Parallel transmission of data is obviously faster than serial transmission because all the bits are
travelling at the same time. However, because of the fine tolerances in the transmission, it is less
reliable as the bits can become muddled up. If one bit is delayed because of the resistance on its wire,
for example, it may arrive in time to be counted as a bit in the next byte! This problem, where the bits
become out of sequence, is called “skew”. Parallel transmission is only suitable for short distances.
Show understanding of the need to check for errors
When data, of whatever type, are transmitted from one device to another, they are transmitted as a
series of binary digits. Any data that are transmitted are going to be made up of a very large number
of bits.
Consequently, there are bound to be occasions on which the data are not transmitted correctly or on
which they become corrupted during transmission. There are only two possible types of error that can
occur; either a 1 is received as a 0 or a 0 is received as a 1. Mistakes rarely occur, but when they do
occur they can be very serious, as the data are no longer correct. This makes it important that there
should be methods for checking the data when they are transmitted.
Explain how parity bits are used for error detection
A parity check involves checking that the number of 1 bits in a byte totals to an even number (called
“even parity”) or an odd number (called “odd parity”). If two devices that are communicating decide
to use odd parity, there must always be an odd number of 1s. If a
byte is received with an even number of 1s, an error must have occurred. For example, the byte
01011000 is sent. It has three 1 bits so it passes the odd parity check. When it is
transmitted, the byte received is 11011000. This has four 1 bits, which is an even number,
so there must have been an error in transmission. The receiving device would ask for it to be sent
again. Although this example uses odd parity, even parity can equally well be used. The
two devices have to agree which type of parity to use.
Identify current uses of serial and parallel data transmission such as
Integrated Circuits (IC), Universal Serial Bus (USB)
Serial transmission of Data
Practically all long-distance communication transmits data one bit at a time, rather than in parallel,
because it reduces the cost of the cable.
Keyboard and mouse cables and ports are almost invariably serial -- such as PS/2 port and Apple
Desktop Bus and USB. The cables that carry digital video are almost invariably serial -- such as
coax cable plugged into a HD-SDI port, a webcam plugged into a USB port or Firewire port,
Ethernet cable connecting an IP camera to a Power over Ethernet port, FPD-Link, etc.
An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a
microchip) is a set of electronic circuits on one small plate ("chip") of semiconductor material,
normally silicon. ICs can be made very compact, having up to several
billion transistors and other electronic components in an area the size of a fingernail.
Integrated circuits are used in virtually all electronic equipment today and have revolutionized the
world of electronics. Computers, mobile phones, and other digital home
appliances are now inextricable parts of the structure of modern societies, made possible by the low
cost of producing integrated circuits. Solid State storage use integrated circuits, for example, flash
Many communication systems were generally originally designed to connect two integrated circuits
on the same printed circuit board, connected by signal traces on that board (rather than external
Integrated circuits are more expensive when they have more pins. To reduce the number of pins in a
package, many ICs use a serial bus to transfer data when speed is not important. Some examples of
such low-cost serial buses include SPI, I²C, UNI/O, and 1-Wire.
Parallel transmission of Data
If you have a printer connected to your computer, there is a good chance that it uses the parallel
port. While USB is becoming increasingly popular, the parallel port is still a commonly used
interface for printers.
Parallel ports can be used to connect a host of popular computer peripherals:
CD burners
External hard drives
Iomega Zip removable drives
Network adapters
Tape backup drives
Part 2 Internet principles of operation
Show understanding of the role of the browser and Internet server
LANs and WANs
In schools, colleges and offices around the world, computers are connected together in
some way to form a network. These vary from local area networks (LAN) as found in school, for
example, to massive wide area networks (WAN) such as the Internet.
LANs essentially allow the sharing of resources both hardware and software, easier communication
between users and the ability to control and monitor computer use. The LANs usually have some
form of file server (where common files and software are stored) and print server. LANs are
frequently connected together to become part of a wide area network and made use of, for example,
routers and broadband modem.
The Internet
The internet is a world-wide system of computer networks. It is possible to access any computer
connected to this network provided you are given the necessary permissions.
A protocol is a set of rules which is used by computers to communicate with each other across a
In reality, the internet took off in the 1990’s with the introduction of HTML (Hypertext mark up
language) and WWW (World Wide Web) which uses http (hypertext transfer protocols)
In order for a computer to operate on a network, there are a range of different components that are
A Router is a device that transfers data from one network to another in an intelligent way. It has the
task of forwarding data packets to their destination by the most efficient route. In order to do this, the
router has a micro computer inside it. This holds a table in memory that contains a list of all the
networks it is connected to, along with the latest information on how busy each path in the network is,
at that moment. This is called the 'routing table'.
When a data packet arrives, the router does the following:- Reads the data packet's destination address
- Looks up all the paths it has available to get to that address
- Checks on how busy each path is at the moment
- Sends the packet along the least congested (fastest) path
Other tasks the Router can perform:
- Exchange protocol information across networks
- Filter traffic - helps prevent unathorised intrusion by malware
Routers are also needed to enable a computer to connect to the internet, after all, the internet is
just one vast external network.
If the data packet has a destination address outside the local networks, then the router may send it to
the internet modem and then on to the ISP's router at the other end of the line. Their router will then
pass forward the data packet towards its destination. For a computer say in the UK to connect to a web
server in the USA the data packet will pass through many routers around the world.
Network cards are needed if the computer does not have a built-in network chips on the motherboard.
They allow the signal from the network to be transmitted to the machine – this could be via a fixed
cable, infra red or radio waves.
A modem converts the digital data from the computer into a continuous analogue wave-form that the
telephone system is designed to deal with (MODulation). The reason for this is that the telephone
system was originally designed for the human voice i.e. continuous
signals. The modem also converts the analogue signal from the telephone network back into
digital data that the computer can understand. (DEModulation). Hence the word
Standard ADSL modems come in two forms: An external box that links to your computer through
an USB port or network cable, or an internal modem that is plugged directly to the motherboard
inside the computer.
In addition to telephone modems, radio has now become very popular as a means of connecting to
the internet. The device that allows you to do this is called the Wi-Fi modem
Web browser
Web browsers are software that allow a user to display and interact with web pages and files from the
The software interprets the coding language of the websites and displays the translation instead of
showing the actual coding. Consequently, a user can simply launch a web browser by clicking on
the appropriate icon from the desktop and there is no need to know
the commands which are required to interpret the website coding once it has been accessed.
A server is software that responds to the requests of other programs, known as clients. In a web server
the software handles web pages so that remote internet users can communicate with the website. The
server accepts and processes these requests and supplies the resources required from the website.
Web servers are also embedded in many devices such as webcams, routers and printers.
Distinguish between HTML structure and presentation
The makeup of a webpage could be viewed as a combination of the following four elements:
Content is the collective term for all the browser-displayable information elements such as text,
audio, still images, animation, video, multimedia, and files (e.g., Word, PowerPoint, PDF, etc.)
of web pages. Content does not require any additional presentational markups or styles in order
to fully convey its message.
Structure refers to the practice of using HTML on content to convey meaning and to
describe how blocks of information are structured to one another. Examples: "this is a list" (ol, ul,
li), "this is headings and subheadings" (<h1>, <h2>, ..., <h6>), "this section is related to" (<a>),
Presentation (or Style) refers to anything related to how the content and structure is
presented. Examples: size, colour, margins, borders, layout, location, etc.
Behaviour (or Interactivity) refers to the employment of client-side script (e.g.,
JavaScript) to create interactivity between the webpage and its users.
Often, a clear distinction between content and structure is difficult, because content could also be
viewed as the information with its semantic coding as well as its structure. In practice, the makeup
of a webpage can simply be viewed as a combination of three elements: Structure, Presentation,
and Behaviour.
The term essentially refers to the "separation of the content made meaningful by structure and the
presentation, ” or simply the "separation of the structure (HTML) and presentation (CSS)".
(source: P. Griffiths, "HTML Dog: The Best-Practice Guide to XHTML&CSS, " New Raider, 2007)
The Practice
Ideally, the separation of structure and presentation will produce an HTML document which
contains the content and structure and a separate CSS file which contains everything that
controls presentation.
The perfect website separation system will store content in a database for a complete isolation
and management of content information. Structure, on the other hand, is dealt
with through a collection of template package built by a server-side scripting language like
PHP or ASP.net.
Show understanding of the concept of Media Access Control (MAC) address,
Internet Protocol (IP) address and cookies
Protocols are the rules used for devices to communicate. TCP/IP stands for Transmission Control
Protocol/Internet Protocol. TCP/IP is a set of rules that looks after data transmission on the internet.
TCP/IP allows networks of different types to communicate with each other.
Internet Protocol (IP) Address
Each computer on a TCP/IP network has an IP address. This is a 32-bit numerical identifier, for
example, 10000011 01101011 00010000 11001000. Each group of eight bits is called an octet. Each
octet can store numbers ranging from 0 to 255. Binary digits are hard for a human to work with, so the
address is normally quoted in four groups for decimal numbers, for example, IP
addresses can be permanently allocated to a device (static addressing), but they can alternatively be
allocated as needed (dynamic addressing), so a particular computer will not always have the same IP
address each time it connects. This saves the network administrator effort and makes efficient use of
the addresses available. These can locate a resource on a network by its IP address.
Because of the huge growth of the internet, in order to make sure that there are enough addresses,
there has been a move towards 128-bit addresses.
When you access a web page on the internet, you have to tell your browser the address to go to.
Long numbers are hard to remember, so we normally use domain names liked
chesterhouse.co.za instead. There are special servers called DNS servers that convert domain
names such as chesterhouse.co.za into numerical IP addresses.
MAC Address
MAC stands for Media Access Control. Each physical interface connected to a network, such as a
network card, has a unique number written to the device by the manufacturer.
The MAC address is used to identify a device on a network. Some switches, known as level
2 switches use MAC addresses to identify devices on a network.
A MAC address is usually given as six pairs of hexadecimal numbers, for example,
A cookie, also known as an HTTP cookie, web cookie, or browser cookie, is a small piece of data sent
from a website and stored in a user's web browser while the user is browsing that website. Every time
the user loads the website, the browser sends the cookie back to the server to notify the website of the
user's previous activity.[1] Cookies were designed to be a reliable mechanism for websites to remember
stateful information (such as items in a shopping cart) or to record the user's browsing activity
(including clicking particular
buttons, logging in, or recording which pages were visited by the user as far back as months or years
Show understanding of what is meant by hypertext transfer protocol (http)
and Hypertext Markup Language (HTML)
HTML (Hypertext Mark up Language)
This is a type of computer language; all the text, graphics and design elements of a webpage are
tagged with codes that instruct a web browser to display the files on a computer screen. It is easy
to see this when looking at the extension name of the file i.e.
.html or .htm which will be shown at the end; for example:
http (hypertext transfer protocol)
This is a set of rules for transferring files on the web; https was later developed to allow secured
transactions on the web to take place. In theory, https works by transmitting the usual information
by using some form of encryption; this should mean that the information cannot be accessed by
anybody other than the client (user) and end server.
Part 3 Data storage
Show understanding that sound (music), pictures, video, text and numbers are
stored in different formats
Each type of application software has its own set of standard file types. The following list
illustrates examples of each format but is not an exhaustive list.
AIFF (Audio Interchange File Format)
GIF (Graphics Interchange Format)
TIFF (Tab Image File Format)
EPS (Encapsulated Postscript)
PCD (Kodak Photo CD)
MOVIE (also .QT)
ASCII, TXT (text only), text with break lines
RTF (Rich text format)
PS (Postscript file)
DOC (Microsoft word file format)
TSV (Tab separated variable)
CSV (Comma Separated variable)
SYLK (Symbolic Link)
DIF (Data interchange format)
DBF (dbase format)
Identify and describe methods of error detection and correction such as parity
checks, check digits, checksums, Automatic Repeat reQuests (ARQ)
Parity Checks
This is used to check data following potential transmission errors; an extra binary digit is added to
each binary number before transmission. Systems that use EVEN parity have an even number of 1s;
systems that use ODD parity have an odd number of 1’s.
For example, if a system uses EVEN parity and the number being transmitted is: 1101110 then an
extra 1 is added to give the number even parity i.e. 11011101; but if the number being transmitted
was: 1101100 then an extra 0 is added since the number already has an even number of 1s i.e.
11011000. The parity is checked at the receiving end to make sure none of the binary bits have been
transmitted incorrectly.
Check digits
This is an extra digit added to a number which is calculated from the other digits; the computer
recalculates the check digit after the number has been input. Check digits are used on bar code
numbers and ISBN’s.
There are a number of ways that check digits are generated; in the example that follows, we will
consider the ISBN-10 method which makes use of the modulo 11 system.
We will consider the number 0-221-43256-?
The position of each digit is first considered:
Digit Position
Each digit in the number is then multiplied by it’s digit position and the totals are
added together:
i.e. (0x10) + (2x9) + (2x8) + (1x7) + (4x6) + (3x5) + (2x4) + (5x3) + (6x2)
= 0+18+16+7+24+15+8+15+12
= 115 total
The total is then divided by 11 (modulo 11) and the remainder, if any, is
subtracted from 11. The answer then gives the check digit.
i.e. 115/11 = 10 remainder 5
i.e. 11 – 5 = 6 (check digit)
hence, the final number is: 0-221-43256-6
A checksum is a way of summarising a block of data such as a USB or a network data packet. At its
simplest, it consists of the arithmetical sum of all the numerical values of all the elements of the
block. The sum is reduced to a standard number of digits and transmitted with the block. When the
block of data gets to its destination, the same mathematical calculation is performed on the data by
the receiving device and the results is
compared with the received checksum. If the two checksums match, the integrity of the data has been
maintained. If the two checksums do not match then an error has been made in
transmitting the data and the receiving device requests the sending device to re-transmit the
data. Even if one binary digit has changed in the data, the recalculated checksum does not match the
received checksum and the data are rejected.
Checksum is similar in function to a parity bit for a byte or a check digit for a code number. More
complex implementations of checksum involve more complex arithmetic to try to detect a wider range
of errors.
Automatic Repeat reQuest (ARQ)
Automatic Repeat reQuest (ARQ), also known as Automatic Repeat Query, is an error- control
method for data transmission that uses acknowledgements (messages sent by the receiver indicating
that it has correctly received a data frame or packet)
and timeouts (specified periods of time allowed to elapse before an acknowledgment is to be received)
to achieve reliable data transmission over an unreliable service. If the sender does
not receive an acknowledgment before the timeout, it usually re-transmits the frame/packet
until the sender receives an acknowledgment or exceeds a predefined number of retransmissions.
The types of ARQ protocols include
Stop-and-wait ARQ
Go-Back-N ARQ
Selective Repeat ARQ
Show understanding of the concept of Musical Instrument Digital Interface
(MIDI) files, jpeg files, MP3 and MP4 files
Musical Instrument Digital Interface (MIDI)
MIDI is a technical standard that describes a protocol, digital interface and connectors and allows a
wide variety of electronic musical instruments, computers and other related devices to connect and
communicate with one another. A single MIDI link can carry up to sixteen channels of information,
each of which can be routed to a separate device.
MIDI carries event messages that specify notation, pitch and velocity, control signals
for parameters such as volume, vibrato, audio panning, cues, and clock signals that set and
synchronize tempo between multiple devices. These messages are sent to other devices
where they control sound generation and other features. This data can also be recorded into
a hardware or software device called a sequencer, which can be used to edit the data and to play it back
at a later time.
MIDI technology was standardized in 1983 by a panel of music industry representatives, and is
maintained by the MIDI Manufacturers Association (MMA). All official MIDI standards are jointly
developed and published by the MMA in Los Angeles, California, US, and for Japan, the MIDI
Committee of the Association of Musical Electronics Industry (AMEI) in Tokyo.
Advantages of MIDI include compactness (an entire song can be coded in a few hundred lines, i.e.
in a few kilobytes), ease of modification and manipulation and choice of instruments.
JPEG (seen most often with the .jpg extension) is a commonly used method of lossy compression
for digital images, particularly for those images produced by digital photography. The degree of
compression can be adjusted, allowing a selectable trade-off
between storage size and image quality. JPEG typically achieves 10:1 compression with little
perceptible loss in image quality.
JPEG compression is used in a number of image file formats. JPEG/Exif is the most common
image format used by digital cameras and other photographic image capture devices; along with
JPEG/JFIF, it is the most common format for storing and transmitting photographic images on the
World Wide Web. These format variations are often not distinguished, and are simply called
The term "JPEG" is an acronym for the Joint Photographic Experts Group, which created the standard.
JPEG/JFIF supports a maximum image size of 65535×65535 pixels.
MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is an encoding format
for digital audio which uses a form of lossy data compression. It is a common audio format for
consumer audio streaming or storage, as well as a de facto standard of digital audio compression for
the transfer and playback of music on most digital audio players.
MP3 is an audio-specific format that was designed by the Moving Picture Experts
Group (MPEG) as part of its MPEG-1 standard and later extended in MPEG-2 standard.
The use in MP3 of a lossy compression algorithm is designed to greatly reduce the amount
of data required to represent the audio recording and still sound like a faithful reproduction of the
original uncompressed audio for most listeners. An MP3 file that is created using the
setting of 128 kbit/s will result in a file that is about 1/11 the size of the CD file created from
the original audio source. An MP3 file can also be constructed at higher or lower bit rates, with
higher or lower resulting quality.
The compression works by reducing accuracy of certain parts of sound that are considered to be
beyond the auditory resolution ability of most people. This method is commonly referred to as
perceptual coding. It uses psychoacoustic models to discard or reduce precision of components less
audible to human hearing, and then records the remaining information in an efficient manner.
MPEG-4 Part 14 or MP4 is a digital multimedia format most commonly used to
store video and audio, but can also be used to store other data such as subtitles and still images. Like
most modern container formats, it allows streaming over the Internet. The only
official filename extension for MPEG-4 Part 14 files is .mp4. MP4 files work in a similar way to
MP3, but they store audio, video, photo and animation files.
Show understanding of the principles of data compression (lossless and lossy
compression algorithms) applied to music/video, photos and text files
When data other than text is being transmitted, e.g. on the Internet, it is important to limit the amount
of data that needs to be sent to stop the time taken to download the data being unreasonably long. The
amount of data can be limited by reducing the file size of pictures so that they take up only a small part
of the screen or restricting them to a few colours. Speeding up the transmission of the data is achieved
by reducing the amount of data that is sent. This is known as file compression.
Compression can be either lossy or lossless. Lossless compression means that no data is lost.
Lossy Compression
Lossy compression involved sacrificing some of the data in order to reduce the file size. Lossy
compression techniques reduce the quantity of data in two ways. First by using complex
mathematical encoding and secondly by deliberately losing some types of visual information that
our eyes and brain usually ignore (this is called quantization).
For example, the video frame rate may be reduced from the normal 25 frames per second down to
around 15 frames per second before there is a perceptible loss in quality. The frames themselves
may be treated as separate still images, and compressed individually using JPEG compression.
Different areas of a frame may be compressed by different degrees – an area of blue sky which lacks
detail might be compressed by 25:1, whereas a person’s face might only be compressed by 5:1.
Depending on the amount of action in the video, only some areas of each frame may change from
one frame to the next and only the changed data need be stored. The size of the picture may also be
reduced, reducing the overall quantity of pixels to be stored.
If lossy compression is taken to an extreme, it can result in a significant loss of picture quality.
The higher the compression ratio, the worse the resulting image. For instance, colour fidelity
fades and the edges of objects become very obvious, until eventually the results is unwatchable.
JPEG image compression works in part by rounding off nonessential bits of
information. There is a corresponding trade-off between preserving information and reducing size. A
number of popular compression formats exploit these perceptual differences,
including those used in music files, images, and video.
Lossy image compression can be used in digital cameras, to increase storage capacities with
minimal degradation of picture quality. Similarly, DVDs use the lossy MPEG-2 Video
codec for video compression.
Lossless Compression
Lossless compression uses mathematical techniques such as Huffman coding or Discrete Cosine
Transformation (DCT), to reduce the quantity of information to be stored, while still being capable
of reproducing the original image without any loss in quality.
Lossless data compression algorithms usually exploit statistical redundancy to represent data more
concisely without losing information, so that the process is reversible. Lossless compression is
possible because most real-world data has statistical redundancy. For example, an image may have
areas of colour that do not change over several pixels; instead of coding "red pixel, red pixel, ..." the
data may be encoded as "279 red pixels". This is a basic example of run-length encoding; there are
many schemes to reduce file size by eliminating redundancy.
Compression standards include MPEG, M-JPEG, Cinepak, Intel’s Indeo Video Interactive
(IVI), Apple’s Quicktime, Microsofts Directshow
Part 4 Security
Show understanding of the internet risks associated with viruses, spy-ware and
Show understanding of security aspects of using the internet and
understand what methods are available to help minimise the risks
Hacking is the act of gaining illegal access to a computer system; many hackers do this to cause
harm to a computer system or just to gain personal data (such as credit card numbers) for their own.
Impact of hacking on computer systems:
Gaining access to personal data can lead to fraud, identity theft, or even disclosing personal
information to harm the individual.
Hacking could be used to gain sensitive or key data and even change or delete data once
Safeguards available to remove or minimise the risk:
Use of firewalls
Use robust passwords and user ids
Use of encryption
Anti-hacking software is also available to help prevent hacking.
Viruses are programs that replicate themselves and are designed to disrupt a computer system;
they often work by attaching themselves to computer files.
Impact of viruses on computer systems:
Viruses can cause a computer to crash (i.e. stop functioning normally, lock up or stop it
responding to software).
Viruses can cause loss of files (if system files are lost this can lead to a system crash.)
Viruses can cause corruption of files.
Safeguards available to remove or minimise the risk:
Install and regularly use up to date anti-virus software.
Do not use software from unknown sources (example, from the internet, CDs, etc)
Take care when opening attachments from ‘unknown’ email addresses.
Spyware is software that gathers information by monitoring key presses on the user’s keyboard and
relays this information back to the person who sent the spyware. Spywaare can also install other
spyware programs, read cookies and can even change the user’s web browser.
Impact of spyware on computer systems:
Monitoring key presses gives the originator access to characters in typed passwords, credit
card numbers, sensitive data, etc. and can lead to serious fraud and identity theft implications.
Safeguards available to remove or minimise the risk:
Certain anti-spyware software can identify and remove this type of code/software.
The user should always be alert and look out for ‘clues’ that they are being monitored
in this way.
Malicious, that is harmfully intended, software of all sorts, including but not restricted to,
Explain how anti-virus and other protection software helps to protect the user
from security risks
The most reliable way of detecting and removing malware once it has arrived at a computer is antivirus software, also known as a virus scanner. This software scans files as they are opened, copied
and saved. If malware is detected, it prevents the malware from running. The software by be
configured to automatically or manually remove malware. This consists of remove the malicious
code from a file infected with a virus or deleting the whole of any other sort of malware file.
Some anti-virus software can also monitor a computer for malware activity that could lead to identity
cloning, block a website know to be the source of malware or check links provided by a search engine
for threats. Although anti-virus software is not usually included in an operating system, every
computer should be protected by it and free editions are available
for personal use.
Show understanding of how data is kept safe when stored and transmitted
a) Use of passwords both entered at a keyboard and biometric
User IDs and Passwords
When you log onto your network at school, you have to type in your User ID and Password. This
identifies you to the network as an authorised user.
Any sensible company will ensure that staff need a User ID and Password to gain access to the
system. This should reduce the risk of outsiders being able to get onto the system and damage data.
People should follow rules when choosing their password:
Passwords should be kept secret at all times
Passwords should not be something that is easy to guess such as pet's name or favourite
football team.
Passwords should include text and numbers or symbols
Passwords should be a reasonable length e.g. over 6 characters
Passwords should be changed regularly
Biometric Passwords
Biometrics use physical characteristics, like your face, fingerprints, irises or veins,
or behavioural characteristics like your voice, handwriting or typing rhythm to identify you. Unlike
passwords, your personal traits are extremely difficult to lose or forget. They can also
be very difficult to copy. For this reason, many people consider them to be safer and more
secure than passwords.
Biometrics uses unique features, like the iris of your eye, to identify you. Biometric
systems can seem complicated, but they all use the same three steps:
Enrollment: The first time you use a biometric system, it records basic information about
you, like your name or an identification number. It then captures an image or
recording of your specific trait.
Storage: They analyze your trait and translate it into a code or graph. Some systems also
record this data onto a smart card that you carry with you.
Comparison: The next time you use the system, it compares the trait you present to the
information on file. Then, it either accepts or rejects that you are who you claim to
Systems use the same three components:
A sensor that detects the characteristic being used for identification
A computer that reads and stores the information
Software that analyzes the characteristic, translates it into a graph or code and performs
the actual comparisons
b) Use of firewalls both software and hardware, including proxy
A firewall is a program or hardware device that filters the information coming through the
Internet connection into your personal computer or into a company's network.
It is set up to allow mainly one way access, i.e. you can go out onto the Internet and access pages, but it
checks everything coming back against a set of rules. If the data coming back is from an unauthorised
source, then it is blocked.
You may have heard people saying, 'I can't get on that site at school because it's been blocked';
that is the firewall in action.
Proxy Server
A proxy server is used to protect a network from problems that can be associated with using the
internet. A proxy server will send packets of data from a host on its own network to a server on the
internet. Before sending, however, the proxy server will take the packet of
data apart, check it and reassemble it. It can check for corrupted data, for viruses and for its
destination, which can be blocked if necessary.
The proxy server also inspects packets of data being sent to hosts on its network. Again, it breaks the
packets up, inspects them and reassembles them. Unwanted data, data from unauthorised sites and
corrupted or infected data can be removed.
Sometimes, a proxy server will hide the IP addresses of individual hosts on the network,
exchanging their IP addresses for its own. This adds a level of security from hackers.
Sometimes, proxy servers are set up to cache web pages. As a web page is received, it saves a copy of
it. If the same page is requested again, even by a different host, it can send the page itself rather than
relying on getting it from the internet. This makes access to pages much faster. Proxy servers can
handle FTP transfers and Internet email using SMTP. For both, the proxy server can check all files and
emails that pass through it and can remove any that might have viruses or have been received from
unauthorised sites.
c) Use of Secure Socket Layer (SSL)
Websites need to have a system that protects sensitive data, such as credit card numbers and other
account information, from being accessed by others. The standard method chosen to achieve this
security is to employ a secure socket layer. This is another protocol and it has two distinct features.
The first is to encrypt any data that is being sent and the second is to allow the computer to identify
any server to which data is being sent.
Use of symmetric encryption (plain text, cypher text, use of a key)
Encryption is the scrambling of data so that it becomes very difficult to unscramble and
interpret. Scrambled data is called cypher text. Unscrambled data is called plain text.
Unscrambling cypher text back to the original plain text is called decryption.
Data encryption is performed by the use of a cryptographic algorithm and a key. The algorithm uses
the key to scramble and unscramble the data. Ideally, the algorithm should be made public (so that it
can be scrutinised and analysed by the cryptographic community), while the key remains private.
In symmetric encryption the same key is used to encrypt and decrypt the message. In
asymmetric encryption, one key is used to encrypt a message and another is used to decrypt the
message. This is known as public-key encryption.
Showing understanding that increasing the length of a binary key increases the
strength of the encryption
The key is fundamental to the strength of the encryption. You need the one correct key before you
can decrypt the cypher text. It follows, then, that the longer the key, the greater the range of possible
values it could have. The range of possible values is called the keyspace. The greater the keyspace,
the more difficult it is for an unauthorised person to discover the correct key.
Encryption cannot make unauthorised decryption impossible; it can merely make it improbable.
With unlimited processing capacity and unlimited time available, all cryptosystems could be
broken. The purpose of encryption is to make it as unlikely as possible that a cypher text could
be broken within the period of time during which the contents should remain secret.
Show understanding of the need to keep online systems safe from attacks
including denial of service attacks, phishing, pharming
Denial of Service attacks
In a denial-of-service (DoS) attack, an attacker attempts to prevent legitimate users from accessing
information or services. By targeting your computer and its network connection, or the computers and
network of the sites you are trying to use, an attacker may be able to prevent you from accessing email,
websites, online accounts (banking, etc.), or other services that rely on the affected computer.
Impact of DoS on computer systems:
The most common and obvious type of DoS attack occurs when an attacker "floods" a
network with information. When you type a URL for a particular website into your browser,
you are sending a request to that site's computer server to view the page. The server can only
process a certain number of requests at once, so if an attacker overloads the server with
requests, it can't process your request. This is a "denial of service" because you can't access
that site.
An attacker can use spam email messages to launch a similar attack on your email account.
Whether you have an email account supplied by your employer or one available through a
free service such as Yahoo or Hotmail, you are assigned a specific quota, which limits the
amount of data you can have in your account at any given time. By sending many, or large,
email messages to the account, an attacker can consume your quota, preventing you from
receiving legitimate messages.
Safeguards available to remove or minimise the risk:
Unfortunately, there are no effective ways to prevent being the victim of a DoS attack, but there are
steps you can take to reduce the likelihood that an attacker will use your computer to attack other
Install and maintain anti-virus software
Install a firewall, and configure it to restrict traffic coming into and leaving your
Follow good security practices for distributing your email address. Applying email
filters may help you manage unwanted traffic
Phishing is where the creator sends out a legitimate-looking email in the hope of gathering personal
and financial information from the recipient. As soon as the recipient clicks on the link in the
email/attachment they are sent to a bogus (fake) website where they will be asked for personal
Impact of phishing on computer systems:
Access to personal information, such as credit card numbers, PINs, etc., can lead to fraud and
other illegal use of whatever personal and financial information the creator can get.
Safeguards available to remove or minimise the risk:
Many ISPs can filter out these phishing emails, but users should always be aware of the risk
and exercise caution when opening emails.
Pharming is where malicious code software is installed on the hard drive of the user’s computer or on the
actual web server. This code will re-direct users to bogus (fake) websites without the user’s consent or
knowledge. Unlike phishing, which requires the user to open an email, in pharming there is no need for the
user to consciously take any action.
Impact of pharming on computer systems:
Access to personal information, such as credit card numbers, PINs, etc., can lead to fraud and other
illegal use of whatever personal and financial information the creator
can get.
Safeguards available to remove or minimise the risk:
Certain anti-spyware software can identify and remove pharming code.
The user should always be alert and look out for ‘clues’ that they are being re- directed to
another site.