AS IT

Paul Long, Sarah Lawrey and Victoria Ellis

Cambridge International
AS and A Level

IT

Coursebook

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Content Contents

Introduction viii
  1
1 Data, information, knowledge and processing  23
2 Hardware and software  54
3 Monitoring and control  61
4 E-safety and health and safety  71
5 The digital divide  78
6 Using networks  95
7 Expert systems 102
8 Spreadsheets 136
9 Database and file concepts 175
10 Sound and video editing 188
11 Emerging technologies 200
12 The role and impact of ICT in society 210
13 Networks 232
14 Project management 249
15 System life cycle 270 iii
16 Graphics creation 280
17 Animation 285
18 Mail merge 295
19 Programming for the web 308
313
Glossary 333

Answers

Acknowledgements

Cambridge International AS and A level IT

How to use this book: a guided tour

iv

How to use this book: a guided tour

v

Chapter XX: Chapter title

Introduction

This full-colour, illustrated textbook has been written by experienced authors specifically for the
Cambridge International AS and A Level Information Technology syllabus (9626).

The qualification replaces A-Level Applied ICT. The new syllabus develops a broad range of IT skills.
Throughout the book there are examples of IT in practice, tasks for students to complete, discussion
points or extension exercises to provoke further thought and discussion and questions that will
test students’ knowledge and understanding. Whenever a task is presented, we would encourage
students to carry it out before progressing further.

The syllabus defines three assessment objectives: AO1 Recall, select and communicate knowledge
and understanding of IT, AO2 Apply knowledge, understanding and skills to produce IT-based
solutions and AO3 Analyse, evaluate, make reasoned judgements and present conclusions. Each
chapter defines a set of learning objectives which closely match these assessment objectives and
a series of key concepts (hardware and software, network, the internet, system life cycle, new
technologies) recur throughout the syllabus. This coursebook has been written to reflect these, in
particular in the following chapters: the impact of information technology (Chapter 12); hardware
and software (Chapter 2); network (Chapter 13); the internet (Chapters 4 and 19); system life cycle
(Chapter 15); new technologies (Chapter 11). It is not necessary to work through the book in order
from start to finish.

The content of the syllabus is geared towards current practice and practical applications of

vi

computers in everyday life. To reflect this, the practical elements of the book are not concerned
with, for example, providing step-by-step advice on how to use particular software, but rather with
helping students to discover what is available and have the confidence to apply their knowledge to
different types of software. This will help to prepare students for the many different aspects of using
computers that they will encounter in life, and not just for an exam.

Chapter 1 1
Data, information, knowledge 1
and processing

Learning objectives

By the end of this chapter, you will be able to:

■ define the differences between data, information and knowledge
■ define static and dynamic data
■ compare static information sources with dynamic information sources
■ define direct and indirect data sources
■ understand the advantages and disadvantages of gathering data from direct and indirect data sources
■ understand how the accuracy, relevance, age, level of detail and completeness of information can affect its quality
■ describe the coding of data and discuss its advantages and disadvantages
■ evaluate the need to encode data and analyse different methods for encoding data
■ define encryption and describe different methods of encryption
■ evaluate the need for encryption and how it can be used to protect data
■ discuss encryption protocols
■ define validation and analyse a range of validation methods
■ define verification and analyse verification methods
■ explain the need for both validation and verification
■ define proof reading

Cambridge International AS and A level IT

1.01 Data, information and Information
knowledge
When data items are given context and meaning, they
KEY TERMS become information. A person reading the information will
then know what it means.
Data: raw numbers, letters, symbols, sounds or images
without meaning Data is given context by identifying what sort of data it is. This
Information: data with context and meaning still does not make it information but it is a step on the way to
Knowledge: information to which human experience has it becoming information as shown in the next example.
been applied
EXAMPLE

Data Data Context Comment
P952BR
Data is raw numbers, letters, symbols, sounds or images A product This is a product code
with no meaning. code but it is still not known
what it is a product code
EXAMPLE @bbcclick A Twitter for so it is still data.
handle
P952BR This is an address used
@bbcclick for Twitter but it is not
information unless it is
359 known to be a Twitter
23557.99 handle or used within
Twitter software. It’s
2 also not known whose
address it is.
359 Price in
Pakistani This is a currency value
Rupees but it is not known what
the price is for, so it is
still data.

For the data to become information, it needs to be given
meaning. Information is useful because it means something.

Figure 1.01 - Example of raw data. EXAMPLE

The data P952BR could have several meanings. It could Data Context Meaning
possibly be: P952BR
A product A product code for a can
• a product code @bbcclick code of noodles.
• a postal / ZIP code
• a car registration number. A Twitter The Twitter address
handle for the BBC’s weekly
As it is not known what the data means, it is meaningless. technology show, Click,
359 Price in which is worth watching
DISCUSSION POINT Pakistani on BBC World News and
When answering a question such as ‘Give one item of data’, rupees BBC2 to keep up to date
do not try to explain what the data means because it then with technology.
becomes information. Just give the raw numbers, letters,
symbols or image. The price of a mobile
phone cover.

Chapter 1: Data, information, knowledge and processing

Knowledge 1.02 Sources of data

Knowledge is basically what a person knows. This KEY TERMS
is known as their knowledge base. A knowledge base
gets larger over time as a person gains experience or Static data: data that does not normally change
learning. Knowledge requires a person to understand Dynamic data: data that changes automatically without user
what information is, based on their experience and intervention
knowledge base. Crown Prince Salman was appointed Direct data source: data that is collected for the purpose for
Crown Prince of Saudi Arabia on 18 June 2012. This is which it will be used
information. Knowing that he had been Crown Prince Indirect data source: data that was collected for a different
for 2 years on 1 August 2014 is knowledge. Knowledge purpose (secondary source)
allows data to be interpreted. In computing terms,
knowledge is also what a machine knows through the Static data
use of a knowledge base consisting of rules and facts,
often found in knowledge-based systems, modelling and
simulation software.

EXAMPLE

Information Knowledge 3

100km/h is the speed Travelling at 120km/h on
limit on expressways in expressways in Pakistan
Pakistan. is illegal.

A red traffic light means
a car should stop.

Figure 1.03 - A good example of static data.

Figure 1.02 - A red traffic The price of a mobile Static means ‘still’. It is data that does not normally
light. phone cover is more change. Static data is either fixed or has to be changed
expensive than a cup of manually by editing a document.
359 Pakistani rupees coffee.
is the price of a mobile EXAMPLE
phone cover.
• title of a web page
QUESTIONS • magazines
• CD-ROMs
A company creates websites using style sheets. • column headings for a football league table
1 Identify one item of data that will be used by the
(e.g. P, W, D, L, F, A, GD)
company. • instructions on a data entry screen.
2 Describe how this item of data can become information.
3 Describe the term knowledge. Dynamic data

Dynamic means ‘moving’. It is data that updates as a result
of the source data changing. Dynamic data is updated
automatically without user intervention.

Cambridge International AS and A level IT

Static information sources compared with
dynamic information sources

Static information Dynamic information
source source

The information does not Information is updated
change on a regular basis. automatically when the
original data changes.

The information can go out It is most likely to be up

of date quickly because to date as it changes

it is not designed to be automatically based on the

changed on a regular basis. source data.

The information can be An internet or network
viewed offline because live connection to the source
data is not required. data is required, which can
be costly and can also be
slow in remote areas.

It is more likely to be The data may have been
accurate because time will produced very quickly and
have been taken to check so may contain errors.
the information being
4 published, as it will be
available for a long period
Figure 1.04 - This weather map, from the Met Office of time.
website, is an example of dynamic data.
Table 1.01 - Static and dynamic information sources.
EXAMPLE
DISCUSSION POINT
• live sports results on a website (when a goal is
scored, the scores will update on the website) Some people get a little confused by dynamic data
because they think it can be any data that changes at
• news feeds on a mobile phone app (when the news any time. For example, some people think that any
is changed in the main database, the news feed will website includes dynamic data. However, if you look at
be updated on the phone) www.aljazeera.com/contactus, the information on this
page is mainly static, with links to other pages. Although
• availability of tickets for a concert (when somebody it can be changed, it can only be done by changing the
books a ticket, the ticket is no longer available) actual data on the page, whereas dynamic data changes
because the original source has changed. If you look at
• product prices for a till/point of sale (if a price is www.aljazeera.com/programmes, you will see that most of
reduced or increased in the database, this new the information on this page is sourced from programme
price will be used the next time the barcode is schedules and programme information, which will be stored
scanned) in another database. This makes it dynamic data because it
will update when a new programme is scheduled.
• train expected arrival times (these will update
automatically based on the train’s position) TASK

• profit for a product in a spreadsheet (profit = price Look at the Al Jazeera website www.aljazeera.com and
– cost so when either the price or cost changes, identify which data is static and which data is dynamic
then the profit changes too) (updates automatically).

Chapter 1: Data, information, knowledge and processing

Direct data source Data collected from an indirect data source (secondary
source) already existed for another purpose. Although it
Figure 1.05 Direct data source. can still be collected by the person who intends to use it, it
Data collected from a direct data source (primary was often collected by a different person or organisation.
source) must be used for the same purpose for which it
was collected. It is often the case that the data will have EXAMPLE
been collected or requested by the person who intends to
use the data. The data must not already exist for another The sports shop could use various indirect sources
purpose though. When collecting the data, the person to find out what other shops are charging for
collecting should know for what purpose they intend to trainers including:
use the data.
• carrying out a survey of customers who have
EXAMPLE purchased trainers from the other shops (the price
was originally given to the customer for the purpose
A sports shop wants to find out what other shops of selling the trainers which may have been given
are charging for trainers. There are various direct on a different date to when it is now being used or it
sources that this data can be collected from. These may have been discounted at the time)
could include:
• visiting the other shops and noting down the prices • looking at till receipts from the shop (the price is
• visiting the other shops’ websites and noting down printed on the till receipt for the purpose of providing
proof of purchase, not for identifying prices).
the prices
• carrying out a survey of other shop owners to ask their TASK 5

prices (although they are unlikely to want to give these). Which of the following are direct data sources and which
are indirect data sources?
Indirect data source
Data Reason collected Reason used
Figure 1.06 Indirect data source.
Names To record their To contact
and email membership members by email
addresses of and to be able to to see if they will
members of a contact them. donate some
political party
money.

Employee To identify when To allow a police
attendance employees officer to check an
dates and attended work employee’s alibi if
times and to calculate a crime has been
their wages. committed.

Flight times To compare To decide the best
and prices the prices and flight to use for a
from airline times for a trip to trip to Florida.
websites Florida.

Names, ages For a national To allow a marketing
and addresses census. company to find out
of people which areas have the
highest population
of children.

Weather To record the To show the current
measurements current weather. temperature and
from a weather rainfall on a website.
station

Cambridge International AS and A level IT

DISCUSSION POINT QUESTIONS

Remember that direct data is usually used by the person The spreadsheet below is used to calculate the area of a
that collected it and for the purpose they collected it. driveway.
However, it’s also possible for a person to collect data
from an indirect (secondary) source. For example, if a A BC
journalist is writing a news article and bases his story on
existing news articles, then he has used indirect sources 1 Area calculator
rather than interviewing the people involved in the original
story. 2 Length = 3m

3 Width = 5m

4 Area = 15 m2

Figure 1.07 - Part of a spreadsheet.

Advantages and disadvantages of gathering 4 Identify one item of data that is static.
data from direct and indirect data sources 5 Identify one item of data that is dynamic.

The general rule is that data collected directly for the The builder using the spreadsheet needs to know the
purpose for which it is intended is more likely to be length and width of a driveway for a customer.
accurate and relevant than data that is obtained from
existing data (indirect source). 6 Identify one direct source the builder could use to
find the length and width.

7 Identify one indirect source the builder could use to

Direct data source Indirect data source find the length and width.

The data will be relevant Additional data that is not 8 Give one advantage of using the direct source instead
because what is needed required will exist that may of the indirect source to find the length and width.

6 has been collected. take time to sort through

and some data that is 1.03 Quality of information
required may not exist.

The original source is The original source may The quality of information is determined by a number of
known and so can be not be known and so it attributes.
trusted. can’t be assumed that it is
reliable. Accuracy

It can take a long time to The data is immediately Information that is inaccurate is clearly not good enough.
gather original data rather available. Data must be accurate in order to be considered of good
than use data that already quality. Imagine being told that you need to check in at the
exists. airport 45 minutes before the flight leaves, so you turn up
at 18:10 for a 19:05 flight only to find that you were actually
A large sample of statistical If statistical analysis is supposed to check in one hour early.

data can be difficult required, then there are EXAMPLE

to collect for one-off more likely to be large Examples of inaccurate information include:

purposes. samples available. • decimal point in the wrong place, for example
$90.30 instead of $903.00 could suggest a product
The data is likely to be Data may be out of date is much cheaper than it really is
up to date because it has because it was collected at
been collected recently. a different time. • misspelling such as ‘stair’ instead of ‘stare’, where
words have completely different meanings
Bias can be eliminated by Original data may be
asking specific questions. biased due to its source. • misplaced characters, such as a licence plate of
BW9EP3T instead of BW93PET.
The data can be collected The data is unlikely to be in
and presented in the the format required, which
format required. may make extracting the
data difficult.

Table 1.02 - Direct and indirect data sources.

Chapter 1: Data, information, knowledge and processing

Relevance EXAMPLE 7

Information must be relevant to its purpose. Having A person orders a pizza. They ask for a large
additional information that is not required means that pepperoni to be delivered. They forgot to say what
the user has to search through the data to find what is type of base they wanted and where it should be
actually required. delivered to. The pizza company does not have
enough information to fulfil the order.
EXAMPLE
A traveller needs to catch a train from Bhopal to
Examples of irrelevant information include: Kacheguda. They phone up to find out the time of
• being given a bus timetable when you want to departure and arrival, but they have to listen to all
the times of the stations in between before they get
catch a train the arrival time at Kacheguda.
• being told the rental price of a car when you want
Completeness
to buy the car
• a user guide for a mobile phone that All information that is required must be provided in order
for it to be of good quality. Not having all the information
includes instructions on how to assemble required means it cannot be used properly.
a plug.
EXAMPLE
Age
A person has booked their car in for a service over the
Information must be up to date in order to be useful. phone. The mechanic tells them the name of the street
Old information is likely to be out of date and but doesn’t give the building number.
therefore no longer useful. When using indirect data
sources, always check when the information was TASK
produced. Look at the invitation below.

EXAMPLE

Examples of out of date information include:
• the number of residents in a town based on a

census from 2011, but 500 new homes have been
built in the town since then
• a rugby score that has not been updated for
5 minutes during which time a player scored.

Level of detail Figure 1.08 - Birthday party invitation.

There needs to be the right amount of information for Describe how accuracy, relevance, level of detail and
it to be good quality. It’s possible to have either too completeness affect the quality of information in the
little or too much information provided. If there invitation.
is too much information, then it can be difficult to
find the exact information required. If there is not
enough information, then it is not possible to use it
correctly.

Cambridge International AS and A level IT

QUESTIONS “Hi. FYI i been 2 drs
2 day 4 checkup. He
9 Identify three factors that could affect the quality of said im fine but to
information. drink more water
LOL. btw ur picture
10 Describe how the age of information could affect was funny – ROFL."
the quality of information within a user guide for a
mobile phone.

1.04 Coding, encoding and
encrypting data

KEY TERMS

Coding: representing data by assigning a code to it for Figure 1.09 - Text message on a mobile phone.
classification or identification
Encoding: storing data in a specific format EXAMPLE
Encryption: scrambling data so it cannot be understood
without a decryption key to make it unreadable if Using numbers for international dialling codes:
intercepted • 44 = Great Britain
SSL: Secure Sockets Layer • 33 = France
TLS: Transport Layer Security • 49 = Germany
HTTPS: hypertext transfer protocol secure • 34 = Spain
8 • 93 = Afghanistan
• 971 = United Arab Emirates
Coding data • 81 = Japan
Using abbreviations for international vehicle
You are probably very familiar with coding data registration plates:
already. When you send a text message or instant
message you probably code your data. You might use
codes like:

• LOL = laugh out loud
• ROFL = roll on floor laughing
• FYI = for your information
• BTW = by the way
• 2 = to
• 4 = for
• BRB = be right back.

In a similar way, data stored on a computer can be coded. • GB = Great Britain
Coding is the process of representing data by assigning a • F = France
code to it for classification or identification. • D = Germany (Deutschland)
• E = Spain (España)
Often genders are coded as M for male and F for female.
Clothing can be coded by the type, size and colour:

• DR = dress • AFG = Afghanistan
• 2XL = extra extra large • UAE = United Arab Emirates
• BL = blue • J = Japan
• DR2XLBL = a dress in size extra extra large and colour blue.

Chapter 1: Data, information, knowledge and processing

Advantages and disadvantages of coding data DISCUSSION POINT
Can you see problems that might occur when these
There are a number of reasons for coding data. In the numbers and letters are used in codes?
examples used above, it would take a long time to use all
the letters of a country to dial a telephone number and 0 or o or O
there would not be enough space on the rear of a car to I or L or l or i
display the full country name. Z or 2
7 or 1
The advantages of coding data can be summarised as
shown in Table 1.03.

Presentation Data can be presented in small The disadvantages of coding can be summarised as
Storage spaces, such as on labels or when shown in Table 1.04.
Speed of input listing large amounts of data.
Processing Limited codes There may not be enough codes available
Validation Less storage space is required to use, meaning that more letters or
because less characters are used to numbers need to be added. For example,
Confidentiality store the data. with international vehicle registration
Consistency codes, E is already used for Spain and
Data can be input more quickly so Egypt has to use ET and Ecuador has
because only a few numbers or to use EC. Now that Egypt has taken ET,
letters need to be input instead of Ethiopia can’t use it and so has to use ETH.
whole words or phrases.
Interpretation Codes may be difficult to interpret. For 9
Processors can process data more example, with international vehicle
quickly because they only have to registration codes, somebody might
process the coded data instead of look at ET and assume it is Ethiopia or
the whole word or phrase. look at S and assume it is Spain. It’s
even more difficult when considering
It’s possible to validate data by checking international dialling codes that are
it is a particular length or within a represented by numbers.
certain range or matching other rules.
For example, an international vehicle Similarity Some letters and numbers can be difficult
registration code must be a maximum to distinguish such as O and 0 or Z and
of three letters and not contain any 2, especially if handwritten. With codes,
numbers or symbols. it’s difficult to guess what the value might
be and so mistakes can occur. At least
Sometimes data can be coded so with words it’s possible to guess what the
that it only makes sense to people badly written letter might be.
who know what the codes mean.
Efficiency If a user inputting codes does not know
If the correct codes are used then what code to use, then they will not be
data will be input consistently able to enter the data efficiently. Instead
without spelling errors, making it they will have to look up the code.
easier to be searched or summarised.

Table 1.03 - Advantages of coding.

TASK Missing It’s possible that some information gets lost
information during the process of coding. For example,
Create a coding system for clothing that includes the type if devices on a network are coded as L for
of clothing, size, colour and other information that you laptop, P for printer, D for desktop computer
think is relevant. Show it to a friend. Can they interpret and M for mobile phone, then information
the code efficiently? Did you have any duplicate codes? about whether or not the mobile phone or
Do you think the sizes would be understood by potential laptop is touch screen is lost.
customers?

Table 1.04 - Disadvantages of coding.

Cambridge International AS and A level IT

TASK 084 104 101 032 098 105 103 032 098
097 100 032 119 111 108 102 033
Create a coding system for the names of people in your
class. Show it to a friend. Can they interpret the code Visit the website www.unicode.org/charts or www.
efficiently? Did you have any duplicate codes? unicode-table.com.

Encoding data Choose a language script and then choose a short
sentence (less than ten words). Encode your sentence
When data is encoded, it is stored in a specific format. into UNICODE. Now show the Unicode to a friend
Computers do not recognise text, sound and images in the and see if they can convert it back into the original
sentence.

same way we do. Computers use binary digits which are 1s

and 0s. One means on and zero means off. A typical binary Images
number would look like this: 11011010. Therefore, data
needs to be encoded into a format which the computer Encoding is also used to store images. At the most
understands. Codecs are programs that are used to basic level, images are encoded as bitmaps. A
encode data for images, audio and video. The codecs are Microsoft Windows bitmap includes the following
also needed to read the data. data when encoding an image (this is not the

complete list):

Text

Text is encoded as a number that is then represented by • width of bitmap

a binary number. A common encoding method is ASCII • height of bitmap

(American Standard Code for Information Interchange). • bit count which represents number of colours:

ASCII consists of 256 codes from 0 to 255. Here is a subset ■ 1 = monochrome
10 of the ASCII code table: ■ 4 = 16 colours

■ 8 = 256 colours

Character Decimal number Binary number ■ 16 = 65 536 colours

@ 64 01000000 ■ 24 = 16 million colours

A 65 01000001 • compression type (no compression, eight-bit

B 66 1000010 run-length encoding or four-bit run-length

C 67 1000011 encoding)
a 97 01100001
• horizontal resolution in pixels per metre
b 98 01100010 • vertical resolution in pixels per metre

• raster data (the actual shape of the image
c 99 01100011 in pixels).

Table 1.05 - ASCII code table. For the raster data, we will assume a monochrome
image (black and white). Each bit will represent either
There are other encoding methods, too, such as extended a black or white pixel. A byte consists of eight bits and
ASCII which allows for more characters to be used, so will represent eight pixels. The encoding starts from
particularly for international languages. Other encoding the bottom left of the image, works to the right-hand
methods include Unicode and EBCDIC but you don’t need side and then up to the next row and again from left to
to learn about these. right.

TASK

Visit the website www.ascii-code.com and look at the
ASCII code table. What sentence does the following ASCII
code represent?

Figure 1.10 - Empty raster grid.

Chapter 1: Data, information, knowledge and processing

As the image gets bigger, it takes up a lot of storage sample rate, the higher the quality of the music, but also
space. Therefore a method called run-length encoding the more storage that is required. Each sample is stored
(RLE) can be used to reduce the amount of storage space as binary data. The sample rate is measured in hertz (Hz).
that is used. This is known as compression. RLE takes Typically, music on a CD will use a sample rate of 44.1kHz
consecutive values and combines them together. At a (kilohertz) whereas a simple telephone call would find 8 kHz
basic level, the image above has ten black pixels in a row. sufficient.
Instead of storing ten separate pixels, RLE would store the
quantity and colour, for example ten × black or ten × 1111. The bit depth is the number of bits (1s and 0s) used for
each sound clip. A higher bit depth will give a higher quality
Sometimes when files are compressed, they use lossy sound. CDs use a bit depth of 16 which means 16 bits (0s
compression, which means some of the original data is and 1s) are used. 16 bits gives 65 536 combinations of binary
removed and the quality is reduced. For example, Figure storage.
1.11 shows how the quality of an image can be reduced if
lossy compression is used. The bit rate is the number of bits that are processed every
second. It is measured in kilobits per second (kbps). The
Original Current save settings bit rate is calculated using this calculation:

bit rate = sample rate × bit depth × number of channels

EXAMPLE 11

Figure 1.11 - Lossy compression. A CD sound file has a sample rate of 44.1 kHz
(44 100 Hz), a bit depth of 16 bits and two channels
TASK (left and right for stereo).
Images can be encoded into a variety of different file
types. Find out what the purpose of each of the following bit rate = 44 100 × 16 × 2 = 1 411 200 bps = 1.4 mbps
file types is: (megabits per second)
• JPEG/JPG (Joint Photographic Experts Group)
• GIF (Graphics Interchange Format) That means that 1.4 megabits are required to store
• PNG (Portable Network Graphics) every second of audio. Therefore, we can multiply
• SVG (Scalable Vector Graphics) the bit rate by the number of seconds to find the
file size. So for a 3 minute 30 second audio file (210
seconds):

file size (in bits) = 1 411 200 × 210 = 296 352 000
(296 megabits)

There are eight bits in a byte and we use bytes to
measure storage, so the file size in bits is divided by
eight:

file size (in bytes) = 296 352, 000 ÷ 8 = 37 044 000
megabytes = 37 MB (megabytes)

Sound TASK
When sound is encoded, the sample rate, bit depth and Calculate the file size of a sound file with the following
bit rate are stored. When sound is recorded, it is converted properties:
from its original analogue format into a digital format, which • sample rate = 8 000 bps
is broken down into thousands of samples per second. • bit depth = 16
• channels = 1
The sample rate, also known as the frequency, is the
number of audio samples per second. The higher the

Cambridge International AS and A level IT

The encoding method above does not compress the file • 1024 × 768 (Extended Graphics Array (XGA) – often used
and a typical storage format is WAV (Waveform Audio File
Format), which is used on PCs. However, music files are with digital projectors)
often compressed to allow for efficient streaming across
the internet and to enable lots of music files to be stored • 1280 × 720 (Wide Extended Graphics Array (WXGA) –
on a single storage medium. Compression reduces the file
size. wide screen)

There are two types of compression: lossy compression • 800 × 600 (Super Video Graphics Array (SVGA))
and lossless compression. Lossless compression reduces • 480 × 320 (useful for mobile phones where the screen is
the file size without losing any quality, but it can only
reduce the file size by about 50%. smaller and internet bandwidth could be low).

Lossy compression reduces the file size by reducing the The bit rate for videos combines both the audio and
bit rate, which means that some of the quality is lost. frames that need to be processed every second. The
Most human ears won’t be able to detect the loss in bit rate is the number of bits that need to be processed
quality, but an experienced musician would notice. When every second. A higher frame rate requires a higher bit
compressing an audio file, it is possible to choose the bit rate.
rate. A bit rate of 128 kbps is equivalent to what would be
heard on the radio. Video settings pixels
Width: 1280 pixels
Height: 720 kbps
Bit rate: 8000 fps

Frame rate: 24

EXAMPLE Audio settings

A CD file originally has a bit rate of 1.4 Mbps Audio format: 128 kbps, 48kHz, stereo
12 (1 411 200 bps). This is reduced to 128 kbps (128 000
Estimated file size: 58.14 MB per minute of video
kbps). The original file size was 37 MB. To calculate
the change in file size, divide by the original bit rate Figure 1.12 - Video and audio settings.
and multiply by the new bit rate.

Compressed file size = 37 ÷ 1 411 200 × 128 000 A one hour, eight-bit HD video with 24 fps would require
= 3.36 MB. 334 GB (gigabytes) of storage. This would be far too
much data to download or even broadcast. Therefore,
In this example, the file size has been reduced to compression is required. Compression usually involves
approximately 10% of the original size. reducing the:

Video • resolution
When video is encoded it needs to store images as • image size or
well as sound. Images are stored as frames. A standard • bit rate.
quality video would normally have 24 frames per second
(fps). High definition (HD) uses 50 fps and 60 fps. The These all result in lossy compression. A common lossy
higher the number of frames per second, the more compression format is MP4, which is a codec created
storage that is required, but the higher quality the video by MPEG (Moving Pictures Expert Group). There are also
will be. lossless compression methods such as digital video
(DV).

The size of the image is also important. A HD video will TASK
have an image size of 1920 pixels wide and 1080 pixels
high. The higher the image size, the more storage that is Edit a short video using video editing software. Try saving
required. Other common resolutions include: it with different resolutions, different frame rates and
different audio formats. Compare the file sizes of each
• 7680 × 4320 (8K / ultra high definition) video file that is created.
• 3840 × 2160 (4K / ultra high definition)

Chapter 1: Data, information, knowledge and processing

Advantages and disadvantages Audio Interchange File Format (AIFF) or Advanced Audio 13
of encoding data Coding (AAC) audio files)

Data has to be encoded in order to be stored and • quality of images, sound and videos is lost when files are
processed by a computer system. It is essential that data
is encoded into binary digits (1s and 0s). compressed using lossy compression

One purpose of encoding data is often to reduce the file • text that has been encoded using ASCII or UNICODE needs
size. The advantages of reducing the file size include:
to be decoded using the correct format when it is opened.
• enabling real-time streaming of music and video over If some international characters have been included using
UNICODE and the file is opened as an ASCII file, then the
restricted bandwidth (e.g. home broadband, mobile international characters will not be recognised.
broadband)
TASK
• reducing the time taken to download files Compare the file types that can be opened and saved
• faster downloading of websites with images, music using different graphics software packages.

or video Encryption

• enabling more music and video to be stored on CDs, One specific type of encoding is encryption. This is when
data is scrambled so that it cannot be understood. The
DVDs, flash memory and other storage media. purpose of encryption is to make the data difficult or
impossible to read if it is accessed by an unauthorised user.
Another purpose of encoding is to enable different formats Data can be encrypted when it is stored on disks or other
to be used. The advantages of different formats for images storage media, or it can be encrypted when it is sent across
include: a network such as a local area network or the internet.
Accessing encrypted data legitimately is known as decryption.
• formats such as PNG and GIF enabling transparent
Caesar cipher
backgrounds A cipher is a secret way of writing. In other words it is
a code. Ciphers are used to convert a message into an
• formats such as GIF allowing animated images encrypted message. It is a special type of algorithm which
• formats such as JPG allowing a very large colour depth, defines the set of rules to follow to encrypt a message.
Roman Emperor Julius Caesar created the Caesar cipher
meaning that the image will be of high quality so that he could communicate in secret with his generals.

• formats such as bitmap image file (BMP) including The Caesar cipher is sometimes known as a shift cipher
because it selects replacement letters by shifting along
all the original uncompressed data so that the the alphabet.
image is of the highest possible quality and can be
manipulated EXAMPLE

• formats that are designed for specific software such as In this example the alphabet is to be shifted by three
(+3) letters so that A = D, B = E and so on:
Paint Shop Pro and Photoshop containing layers which
allow for various adjustments to be made to the image Original A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
and being able to enable or remove those layers
Encrypted D E F G H I J K L M N O P Q R S T U V W X Y Z A B C
• vector formats such as SVG storing the shapes rather
So to encrypt the word ‘Hello’, we would use:
than the pixels so that graphics can be enlarged and
reduced without loss of quality due to pixelation. H = K, E = H, L = O, O = R

The main disadvantage of encoding data is the variety of which gives KHOOR.
encoding methods, resulting in a large variety of file types.
Problems include:

• the required codecs may not be installed and so a file

cannot be saved in the desired format

• the necessary codecs must be installed, in order to open

an encoded file

• not all software is capable of opening different file

types

• some hardware such as music and video players only

play files encoded in certain formats (for example, a
CD player may only be able to play MP3 files but not

Cambridge International AS and A level IT

DISCUSSION POINT Symmetric encryption

This is the oldest method of encryption. It requires both
the sender and recipient to possess the secret encryption
and decryption key. With symmetric encryption, the
secret key needs to be sent to the recipient. This could be
done at a separate time, but it still has to be transmitted
whether by post or over the internet and it could be
intercepted.

Sender Recipient
Encrypts using secret key
Decrypts using the same
secret key

Figure 1.14 - Symmetric encryption.

Figure 1.13 - The Enigma machine.

Asymmetric encryption

The Germans used encrypted messages during World Asymmetric encryption is also known as public-key

War II using the Enigma machine. An operator would type cryptography. Asymmetric encryption overcomes the

in a message and then scramble it by using three problem of symmetric encryption keys being intercepted

to five notched wheels. The recipient would need by using a pair of keys. This will include a public key
to know the exact settings of the wheels in order to which is available to anybody wanting to send data, and a
decipher the message. There were 159 × 1018 possible
private key that is known only to the recipient. They key is
combinations.

14 the algorithm required to encrypt and decrypt the data.

Encrypted messages from the Lorenz cipher machine led to

the development of the world’s first electric programmable The process works like this:
computer, Colossus, which helped British code breakers

read encrypted German messages. Sender Recipient

The first major encryption algorithm for computers was Encrypts using recipient’s Decrypts using same
the Data Encryption Standard (DES) used in the 1970s. It public key algorithm using their
used a 56-bit (1s and 0s) key. This offered 70 × 1015 possible matching private key

combinations, but the development of computers meant

that it eventually became possible to ‘crack’ the code. This Figure 1.15 - Asymmetric encryption.
was replaced by the Advanced Encryption Standard (AES)

which uses up to 256-bit keys. This can offer 300 × 1011 In the next example, Tomasz sends a message to Helene.
possible combinations.

Tomasz encrypts the message using Helene’s public key.

Helene receives the encrypted message and decrypts it

using her private key.

TASK This method requires a lot more processing than symmetric
encryption and so it takes longer to decrypt the data.
1 Using the Caesar cipher +3 example above, write an
encrypted message to a friend. Ask your friend to In order to find a public key, digital certificates are required
decipher it. which identify the user or server and provide the public
key. A digital certificate is unique to each user or server.
2 Choose how many letters you are going to shift by and A digital certificate usually includes:
write another encrypted message to a friend. Don’t
tell your friend how many letters you shifted by. Your • organisation name
friend should try to decipher the code by working out • organisation that issued the certificate
which letters appear most commonly. • user’s email address
• user’s country
3 See www.math.uic.edu/CryptoClubProject/CCpacket. • user’s public key.
pdf to create a cipher wheel and use it to encrypt and
decrypt messages.

Chapter 1: Data, information, knowledge and processing

Tomasz to access the data will not be able to understand it. The
data is usually accessed by entering a password or using a
Hello Encrypt fingerprint to unlock the encryption.
Helene!
6EB69570 HTTPS
08E03CE4 Helene’s Normal web pages that are not encrypted are fetched and
public key transmitted using Hypertext Transfer Protocol (HTTP).
Anybody who intercepts web pages or data being sent
Helene over HTTP would be able to read the contents of the web
page or the data. This is particularly a problem when
Hello Decrypt sending sensitive data, such as credit card information or
Helene! usernames and passwords.
Helene’s
private key Hypertext Transfer Protocol Secure (HTTPS) is the
encryption standard used for secure web pages. It uses
Figure 1.16 - Asymmetric encryption example. Secure Sockets Layer (SSL) or Transport Layer Security
(TLS) to encrypt and decrypt pages and information sent
When encrypted data is required by a recipient, the and received by web users. This is the encryption method 15
computer will request the digital certificate from the that is used by banks when a user logs onto online
sender. The public key can be found within the digital banking. A secure web page can be spotted by its address
certificate. beginning with https:// and in addition some browsers
display a small padlock.
Asymmetric encryption is used for Secure Sockets
Layer (SSL) which is the security method used for Figure 1.17 - The ‘s’ after ‘http’ and the padlock indicate
secure websites. Transport Layer Security (TLS) has that this is a secure website.
superseded SSL but they are both often referred to as
SSL. Once SSL has established an authenticated session, When a browser requests a secure page, it will check the
the client and server will create symmetric keys for faster digital certificate to ensure that it is trusted, valid and that
secure communication. the certificate is related to the site from which it is coming.
The browser then uses the public key to encrypt a new
TASK symmetric key that is sent to the web server. The browser
Watch the video about SSL at and web server can then communicate using a symmetric
http://info.ssl.com/article.aspx?id=10241. encryption key, which is much faster than asymmetric
encryption.

Hard disk EXAMPLE

Disk encryption will encrypt every single bit of data stored The web browser requests the certificate from the
on a disk. This is different to encrypting single files. In web server.
order to access any file on the disk, the encryption key will
be required. This type of encryption is not limited to disks Web browser 1 Browser requests certificate Web server
and can be used on other storage media such as backup
tapes and Universal Serial Bus (USB) flash memory. It is Figure 1.18 - Asymmetric cryptography.
particularly important that USB flash memory and backup
tapes are encrypted because these are portable storage The web browser then uses the web server’s public
media and so are susceptible to being lost or stolen. If key to encrypt a new symmetric key and sends that
the whole medium is encrypted, then anybody trying encrypted symmetric key to the web server. The

Cambridge International AS and A level IT

web server uses its own private key to decrypt the 256-bit AES encryption it is virtually impossible for
new symmetric key. somebody to decrypt the data and so it is effectively
protected from prying eyes.

Figure 1.19 - Secure website identification. DISCUSSION POINT

The browser and web server now communicate Most Wi-Fi access points and Wi-Fi routers use encryption.
16 using the same symmetric key. This serves two purposes. The first is to only allow people
who know the ‘key’ (usually a password) to access the
network, so that any unauthorised users cannot gain
access. The second is to encrypt the data, so that it cannot
be understood by somebody ‘snooping’ on the Wi-Fi
network.

Wi-Fi networks are particularly susceptible to ‘snooping’
because no wires are required to connect to the network.
It is possible to sit in a car outside somebody’s house
and see the Wi-Fi network. The ‘key’ stops that person
from accessing the network and also stops that person
from understanding the data that is moving around the
network.

Did you know that if you access a public Wi-Fi hotspot that
is ‘open’ and therefore not encrypted that anybody with
the right software can see what you are sending over the
network, including your emails? This applies to laptops,
tablets and mobile phones or any other device using public
Wi-Fi.

Encryption Decryption

Credit card Symmetric Scrambled Symmetric Credit card QUESTIONS
data key data key data
11 Give two reasons for encoding data.
Figure 1.20 - Symmetric encryption. 12 Explain why encoding is necessary for text.
13 Identify two factors that affect the size of a sound
Email
Email encryption uses asymmetric encryption. This means file.
that recipients of emails must have the private key that 14 Decipher the following text that has been encrypted
matches the public key used to encrypt the original email.
In order for this to work, both the sender and recipient using the Caesar cipher with a shift of +4.
need to send each other a digitally signed message that AIPP HSRI
will add the person’s digital certificate to the contact for
that person. Encrypting an email will also encrypt any 1.05 Checking the accuracy of data
attachments.
KEY TERMS
How encryption protects data
Validation: the process of checking data matches acceptable
Encryption only scrambles the data so that if it is found, rules
it cannot be understood. It does not stop the data from Verification: ensuring data entered into the system matches
being intercepted, stolen or lost. However, with strong the original source
Proof reading: checking information manually

Chapter 1: Data, information, knowledge and processing

Validation EXAMPLE 17

Validation takes place when data is input into a computer When filling in a ‘contact us’ form on a website, it is
system. The purpose is to ensure the data is sensible and essential that an email address is entered. The following
conforms to defined rules. A railway season ticket will have would be valid if only a presence check is carried out:
an expiry date. The season ticket is valid until it expires.
Once it expires it is invalid. The rule here is that the date •a
the season ticket is used must be before its expiry date. • a@b
• [email protected]
When data is validated, if it conforms to the rules then it •@
will be accepted. If it does not conform to the rules, then • 372823
it will be rejected and an error message will be presented. Notice that none of these are correct but they pass
Validation does not ensure that data is correct. the rule that data must be present.

TASK Range check
Create a flow chart to describe the process of validation. A range check ensures that data is within a defined range.
You should include the following: A limit check has a single boundary. This could be the
• Start highest possible value or the lowest possible value.
• End A range check includes two boundaries, which would be
• Input of data the lower boundary and the upper boundary. The following
• Error message symbols are used when comparing with a boundary:
• Data accepted
• Data rejected > greater than
• Validation decision < less than
There are a variety of different validation checks that >= greater than or equal to
can be used to check whether data is acceptable. <= less than or equal to
These different checks are the different types of rules
that are used.

Presence check EXAMPLE
A presence check is used to ensure that data is entered. If
data is entered, then it is accepted. If data is not entered, An opinion poll is taken and asks for the respondent’s
then the user will be presented with an error message age. The respondents have to be at least 18 years old.
asking them to enter data. The lower boundary is 18. There is no upper boundary,
so this is a limit check. This could be written as:
Please fill in the mandatory fields.
Age >= 18
Figure 1.21 - Required data on a website. Letters representing grades for an exam are
entered. Only the letters A–E are valid grades. The
grade must be less than F. The upper boundary is E.
There is no lower boundary, so this is a limit check.
This could be written as:

Grade < F
The number of students in a class must be between
5 and 28. The lower boundary is 5 and the upper
boundary is 28, so this is a range check. This could
be written as:

Number of students >= 5 and <= 28

Cambridge International AS and A level IT

Data that is within the boundaries is valid. Data that Format check
is outside the boundaries is invalid. Data that is A format check ensures data matches a defined format. It
valid and within the boundaries is not necessarily is sometimes known as a picture check and the data has
correct. A grade of C could be entered when a to follow a pattern.
grade A should have been entered. C is valid but
incorrect. EXAMPLE

Type check An email address must include an @ symbol
A type check ensures that data must be of a defined data preceded by at least one character and followed
type. by other characters. The following data would be
valid:
EXAMPLE
• [email protected]
• If an age is entered, it must be an integer.
• If a grade is entered, it must be text with no • [email protected]

numbers. • fdc@jb
• If a price is entered, it must be numerical.
• If a date of birth is entered, it must be a date. A student ID must be four numbers followed by two
letters. The following data would be valid:
Data that is of the correct data type is valid. Data that
18 is valid and of the correct data type is not necessarily • 3827BD

correct. A date of birth of 28/12/2087 could be entered. • 1111AA
The date is valid because it is a date data type, but it is
clearly incorrect. Data that matches the pattern is valid. Data that is valid
and of the defined format is not necessarily correct. An
Length check email address of fdc@jb meets the rules above but is
A length check ensures data is of a defined length or clearly incorrect.
within a range of lengths.
Lookup check
EXAMPLE A lookup check tests to see if data exists in a list. It is
similar to referential integrity in Chapter 9, but uses a list
• A password must be at least six characters long. defined within the validation rule.
• A grade must be exactly one character long.
• A product code must be at least four characters EXAMPLE

and no more than six characters. When asking a user for their gender, they can
respond with ‘Male’ or ‘Female’. A lookup
Data that is of the allowed length is not necessarily validation rule would check to see that the values
correct. For example, a valid date might require six are within this list. Students taking a qualification
digits. A date of 2ndFeb would be a valid length could be issued grades of pass, merit and
because it contains six characters, but it would not distinction. When inputting the data, a validation
be correct because it does not follow the required rule could check that only ‘X’, ‘P’, ‘M’ or ‘D’ are
format. entered (‘X’ would be for fail).

Consistency check
A consistency check compares data in one field with data
in another field that already exists within a record, to see
whether both are consistent with each other.

Chapter 1: Data, information, knowledge and processing

EXAMPLE EXAMPLE

When entering the gender of ‘M’ or ‘F’, a consistency
check will prevent ‘F’ from being entered if the title
is ‘Mr’ and will prevent ‘M’ from being entered if the
title is ‘Mrs’ or ‘Miss’.

When entering data about dispatching products,
it would not be possible to mark an item as being
dispatched until after it has been packaged.

Check digit Figure 1.23 - Unique Product Code check digit. 19
A check digit is a number (or letter) that is added to the
end of an identification number being input. It is a form of The Unique Product Code (UPC) check digit is used
redundancy check because the check digit is redundant with 13 digit barcodes. It is the last digit shown on
(not needed for the identification number, but just used for a barcode. The algorithm for calculating the check
validation). When the identification number is first created, digit is:
an algorithm (a series of calculations) is performed on it to
generate a check digit. When the identification number is 1 Add all the digits in even numbered positions
input, the same algorithm is performed on it. The result of together.
the algorithm should match the check digit. If it matches,
then the data is valid. If it does not match then the data is 2 Multiply the result (1) above by 3.
invalid.
3 Add all the digits in odd numbered positions
Original identification number = 20392 together.
Algorithm is performed on 20392
Check digit = 4 4 Add results (2) and (3) together.

Data including check digit = 203924 5 Divide the result (4) above by 10.

Valid Example 6 Calculate the remainder (modulo 10) of result (5)
Identification number including check digit is entered into the computer: 203924 above.
Algorithm is performed on 20392
Result of algorithm = 4 7 Subtract (6) above from 10.

Result of algorithm (4) is compared with check digit that was entered (4). Valid example
They match. In this example, the International Standard Book
Data is valid. Number (ISBN) is 978095734041-1 where the last
1 is the check digit. To calculate the check digit,
Invalid Example the following algorithm is performed on the ISBN
Identification number including check digit is entered into the computer: 205924 (excluding check digit):
Algorithm is performed on 20592
Result of algorithm = 7 1 Add all the digits in even numbered positions
together (978095734041) : 7 + 0 + 5 + 3 + 0 + 1 = 16.
Result of algorithm(7) is compared with check digit that was entered (4).
They do not match. 2 Multiply result (1) above by 3: 16 × 3 = 48.
Data is invalid.
3 Add all the digits in odd numbered positions
Figure 1.22 - Valid and invalid check digit calculations. together (978095734041) : 9 + 8 + 9 + 7 + 4 + 4 = 41.

There are a variety of calculations that can be 4 Add results (2) and (3) together: 48 + 41 = 89.
performed to determine what the check digit should be.
The important thing is that the same calculation used to 5 Divide the result (4) above by 10: 89 ÷ 10 = 8.9.
create the check digit in the first place should be used to
confirm the check digit when the identification number
is input.

Cambridge International AS and A level IT

6 Calculate the remainder (modulo 10) of result (5) Visual checking
above: 89 MOD 10 = 9. A method of verification can be for the user to visually
check that the data entered matches the original source.
7 Subtract (6) above from 10: 10 - 9 = 1. This can be done by reading the data displayed on
The result of the algorithm is 1. screen and comparing it with the original data. If the data
Invalid example matches, then it has passed the verification process. If it
In this example, the ISBN has been entered does not match, then it has failed the verification process
incorrectly as two numbers have been transposed and needs to be re-entered. Visual checking does not
(7 and 3) accidentally: 978095374041-1. ensure that the data entered is correct. If the original data
1 Add all the digits in even numbered positions is wrong, then the verification process may still pass.
For example, if the intended data is ABCD but ABC is on
together (978095374041) : 7 + 0 + 5 + 7 + 0 + 1 = 20. the source document, then ABC will be entered into the
2 Multiply result (1) above by 3: 20 × 3 = 60. computer and verified, but it should have been ABCD in the
3 Add all the digits in odd numbered positions first place.

together (978095374041) : 9 + 8 + 9 + 3 + 4 + 4 = 37. Double data entry
4 Add results (2) and (3) together: 60 + 37 = 97. Another method of verification is to input data into
5 Divide the result (4) above by 10: 97 ÷ 10 = 9.7. the computer system twice. The two items of data are
6 Calculate the remainder (modulo 10) of result (5) compared by the computer system and if they match, then
they are verified. If there are any differences, then one of
above: 97 MOD 10 = 7. the inputs must have been incorrect.
7 Subtract (6) above from 10: 10-7 = 3.
20 The result of the algorithm is 3. The result 3 is EXAMPLE
compared with the check digit of 1 that was
entered. They do not match. The ISBN entered is When changing a password, most systems will
invalid. ask the user to enter the new password twice.
This is because it is critical that the password is
TASK entered correctly in order that the user can gain
Use the website www.upcdatabase.com/checkdigit.asp access to the system in the future. If the new
to generate check digits for product codes. passwords match, then the password will be
changed. If the new passwords don’t match, then
DISCUSSION POINT one of the passwords must have been entered
The usual algorithm for UPCs is to multiply the odd digits incorrectly.
by 3 rather than the even digits. It is only for 13 character
barcodes that the even digits are multiplied by 3. It is still possible to pass double entry verification and for
Find out how to calculate a check digit for 10 digit the data to be incorrect. If the data is entered incorrectly
barcodes. twice, then the two values may match. For example, if the
CAPS key is left on by mistake then both entries would
Verification match.

Verification is the process of checking that the data The need for both validation and verification
entered into the computer system matches the original
source. As you will have seen in the two sections above, it is
possible to enter valid data that is still incorrect. It is
also possible to verify incorrect data. By using both
validation and verification, the chances of entering
incorrect data are reduced. If data that is incorrect
passes a validation check, then the verification check is
likely to spot the error.

Chapter 1: Data, information, knowledge and processing

EXAMPLE QUESTIONS 21

The validation rule is that a person’s gender must 15 Describe the purpose of verification.
be a single letter. N is entered. This passes the 16 Identify three methods of validation.
validation check but is clearly incorrect. When 17 Explain using examples why validation and
verified using double entry, the user enters N first
followed by M the second time. The verification verification do not ensure data is correct.
process has identified the error.
1.06 Summary
However, it is still possible that the user could enter
N twice and both the validation and verification Information has context and meaning so a person
processes would fail. knows what it means. The quality of information can be
affected by the accuracy, relevance, age, level of detail
Proof reading and completeness of the information. Proof reading is the
process of checking information.
Proof reading is the process of checking information.
For example, when this book was written it was Data are raw numbers, letters, symbols, sounds or
checked for spelling errors, grammar errors, formatting images without meaning. Knowledge allows data to be
and accuracy. Proof reading can take place for a interpreted and is based on rules and facts. Static data
document or when data is input. When proof reading does not normally change. Dynamic data updates as a
a document, it is best to have a proof reader who is result of the source data changing. Data collected from a
different from the original author of the document, direct data source (primary source) must be used for the
as they will be able to check the work objectively and same purpose for which it was collected. Data collected
identify errors. However, it is also possible for the from an indirect source (secondary source) already existed
original author to proof read their own document, but for another purpose.
they may not notice some of their own errors. When
data is input, it is usually proof read by the person Coding is the process of representing data by assigning
inputting the data. a code to it for classification or identification. Encoding
is the process of storing data in a specific format.
TASK Encryption is when data is scrambled so that it cannot be
Check the information below by proof reading it. understood.
I were walking along the road yesterday wen I spotted
a dog without a lead I called the dog but it did not Validation ensures that data is sensible and allowed.
respond. the dog ran away; Validation checks include a presence check, range check,
type check, length check, format check and check digit.
Verification is the process of checking data has been
transferred correctly. Verification can be done visually or
by double data entry.

Cambridge International AS and A level IT

Review questions

1 Give an example of data. [1]
2 Describe the term knowledge. [1]

A news and sports website includes both static and dynamic data.
3a Compare static and dynamic data. [4]
3b Identify and describe two factors that affect the quality of information on the website. [4]
3c Give an example of coded data related to the news and sports website. [1]

The website streams news and sports videos.
3d Explain why the video is compressed when it is encoded. [2]
3e Identify three factors that will affect the size of a video file. [1]
3f Identify and describe two factors that affect the file size of images on the website. [4]

Users can pay for premium services on the website using their credit card.
4a Explain why the website uses https at the beginning of the website address instead of

http. [4]
4b Describe symmetric encryption. [1]

The journalists working for the website encrypt their emails.
22 4c Describe how asymmetric encryption is used with emails. [2]

When the users subscribe to premium features, they have to choose a password.
4d Describe how verification can be used when entering the password. [1]

There is a form on the website that can be used to submit news stories. When data is entered
onto the form, it is validated.
5a Describe the purpose of validation. [1]
5b Using an example related to submitting a news story, identify and describe one method of

validation. [3]

23

Chapter 2
Hardware and software

Learning objectives

By the end of this chapter, you will be able to:

■ define hardware
■ evaluate internal and external hardware devices
■ explain the purpose of and evaluate storage devices
■ explain the purpose of input and output devices
■ evaluate input, storage and output devices for a given task
■ define soft ware
■ evaluate diff erent types of soft ware
■ explain the purpose of system soft ware
■ evaluate application soft ware
■ evaluate user interfaces
■ evaluate mental models
■ describe utility soft ware
■ compare custom-written and off -the-shelf soft ware
■ describe and evaluate a compiler and interpreter

Cambridge International AS and A level IT

2.01 Hardware Remember
The central processing unit (CPU) is the brain of a
KEY TERMS computer. It is the part of the computer that carries out
calculations, executes instructions and processes data. It
Hardware: a physical component of a computer system includes the arithmetic logic unit (ALU) and control unit (CU).
Device: a hardware component of a computer system
consisting of electronic components The ALU performs calculations and logical operations. The
Output device: a device used to communicate data or CU runs the fetch–execute cycle which fetches instructions
information from a computer system from memory and executes them.
Storage device: a device used to store data onto a storage
medium Input data is taken from input devices (such as a
Input device: a device that allows data to be entered into a keyboard) or storage and processed by the CPU, which
computer system produces output data that can be stored or sent to an
Storage medium: the medium on which data is stored output device (such as a monitor).
Volatile: data is lost when there is no power
Non-volatile: data remains when there is no power CPUs usually consist of multiple cores. Each core is
a separate processor, so a quad-core CPU has four
Hardware processors. Processors are measured by the number
of instructions they can process per second (hertz). A
Remember 3 GHz (gigahertz) processor can process up to 3 billion
An item of hardware is a physical component that forms instructions per second.
part of a computer system. Items of hardware are often
known as devices because they comprise electronic Motherboard
24 components. Hardware devices can be internal to the
computer system (such as the central processing unit,
memory or motherboard) or they can be external to the
computer system (such as the monitor, keyboard or mouse).

Hardware is categorised into input, output and storage
devices. Input devices allow data to be sent to a
computer (e.g. keyboard). Output devices allow the
communication of data/information from a computer (e.g.
monitor). Storage devices store data onto a storage
medium so that it can be used at a later time.

Internal hardware devices

Central processing unit

Figure 2.02 - A motherboard.

Figure 2.01 - A central processing unit. Remember

The motherboard is a printed circuit board (PCB) which
connects the main components of a computer. Some
of these components may be an integral part of the
motherboard. Such components can include Universal
Serial Bus (USB) ports, a network port and an integrated
graphics card. A motherboard will always include the main
bus which is used to transfer data between hardware
components.

Chapter 2: Hardware and software

Other hardware components can be connected directly TASK 25
to the motherboard, including random access memory Find out what is the purpose of programmable read only
(RAM), the CPU and expansion cards. Expansion cards memory (PROM) and erasable programmable read only
offer additional functionality, such as enhanced graphics memory (EPROM).
processing and additional USB ports.
Graphics card
Random access memory A graphics card is also known as a video card, display
adapter or graphics adapter. It is a printed circuit board
Remember that connects to one of the motherboard’s expansion
Random access memory (RAM) is memory that is used slots. Its purpose is to generate the signals needed to
to store currently active programs and data. The more display the output image from the computer. Often the
RAM that is available to the computer, the more data and graphics adapter is integrated into the motherboard and
programs can be used at the same time. does not require a separate card. However, by using a
separate card, the graphics performance can be improved
This is particularly important in multitasking as a separate processor can be used for graphics (a
environments, when several programs may be open at the graphics processing unit).
same time.
Figure 2.03 - A graphics card.
When the RAM becomes full, programs or data that are
no longer active will be removed to make space for new Graphics cards include a variety of options for output.
programs or data. If the RAM becomes full and there are Standard video graphics array (VGA) output to a monitor
no inactive programs or data to remove, then an area of is achieved through the RGB port which transmits red,
secondary storage (e.g. hard disc drive (HDD) or solid state green and blue signals to the monitor in an analogue
drive (SSD)) known as virtual memory is used to expand format. High definition display is achieved through a
the amount of memory available to the CPU. Virtual high-definition multimedia interface (HDMI) port. Another
memory is very slow because secondary storage access option is Digital Video Interface (DVI) which supports high
times are thousands of times slower than RAM access resolution displays using digital signals.
times.
Sound card
RAM is volatile, which means the content of the memory The purpose of a sound card is to generate the signals
is lost if there is no power to the RAM. When you are using needed to output sound from the computer to a speaker
a computer and experience a power cut, this is why the or set of speakers. It is often an integrated part of the
data you are currently using is lost unless it has recently motherboard and will include a single output for audio
been saved to secondary storage. (green socket), a single input for a microphone (red socket)

Read only memory
Read only memory (ROM) is memory that, once it has been
written to, can no longer be changed. It is permanent and it
is non-volatile, which means that when there is no power
to the computer, the contents of the ROM will be retained.
This is because it is powered by a small long-life battery.

TIP
In a computer, there is usually some ROM that stores the
instructions to boot (start) the computer.

ROM is also used in small devices such as calculators
where there is only one program or set of instructions.

Cambridge International AS and A level IT

and a single input for line level devices (blue socket). If Attachment (SATA) or Integrated Drive Electronics (IDE)
higher quality or surround sound is required, then it is cable.
usually necessary to have a separate sound card which
connects to one of the motherboard’s expansion slots.
This will enable multiple outputs for front, rear, centre and
sub-woofer speakers.

Hard disk drive Figure 2.05 - Multiple platters.

A hard disk drive (HDD) is the most common form of
secondary storage for a computer due to its relatively low
cost per MB (megabyte). In 2015, hard disk drives could
store up to 8 TB (terabytes) of data with access speeds of
6 GB/s. The hard disk drive consists of two main parts: the
device that is the electronics which store the data, and the
disk that is the medium onto which the data is stored. The
device (or drive) includes a read-write head which sits at
the end of an access arm and magnetises sectors on the
disk (platter).

Access arm Disk (platter)
26
DISCUSSION POINT

Do you know where the phrase ‘my computer has crashed’
comes from? It relates to when the read-write head crashes
into a platter and causes damage to the hard disk, meaning
that data and programs can no longer be retrieved.

Read-write head Solid state drive

Figure 2.04 - A hard disk. A solid state drive (SSD) is another secondary storage
device that is non-volatile. However, there are no moving
There is usually more than one platter and therefore parts and the data is stored onto flash memory. It is also
there will be several read-write heads for each side of not necessary to store data in the same cylinder in order
each platter as shown in Figure 2.05. Each platter will to maximise access speed as the data can be stored
have tracks and each track will be split into sectors. The anywhere on the flash memory and access speeds will
tracks that are in the same position on each platter form not be affected. SSDs are also non-magnetic and so are
a cylinder. Wherever possible, a computer will attempt to not susceptible to damage from to close, strong magnetic
store data on a single cylinder as this requires the least fields.
access arm movement and the access arm is the slowest
part of the hard disk. In 2015, SSDs could store up to 8 TB, but due to the newer
technology were far more expensive than HDDs and were
Data stored on a hard disk is non-volatile. This means more common in capacities of 128, 256 or 512 GB. SSDs
that when the computer is turned off and there is no have access speeds of around 400–600 MBps (two to three
power then the data will still be safely stored on the times faster than a HDD). This means they are used in
hard disc. Hard discs can be internally connected to higher performance computers. A frequent compromise
the computer using a Serial Advanced Technology between speed, capacity and price is to have a smaller
SSD to store the operating system and software (for speed
of access) and use a larger HDD to store data. SSDs also
require a lot less power than HDDs and so are preferred in
laptop and tablet computers.

Chapter 2: Hardware and software

TASK Monitor
Have a look at the inside of an old computer. Identify Although not an essential part of every computer
each of the main components that can be seen on the system, a monitor is certainly an essential part of most
motherboard, the hardware devices that are connected computer systems as it enables the user to visualise the
to it and any available connection ports. output. It is connected to the computer using one of the
ports on a graphics card. Monitor sizes are measured
External hardware devices diagonally and, apart from some very old ‘legacy’
monitors, they now have flat screens which minimalise
Cloud the amount of desk space that is used and they are
Cloud computing is a term that refers to anything where light enough to be mounted on a wall or a desk using a
computing services are hosted over the internet and bracket or on a shelf.
not in the same physical location as the computer being
used. Data is stored on banks of servers that are accessed A monitor will be limited by its resolution. This is
remotely. The physical devices that store the data are the number of pixels it can display and is measured
owned by a hosting company rather than the person or horizontally by vertically. For example, a high definition
organisation using the data. (HD) monitor can display 1920 x 1080 pixels. Some monitors
also include a touch interface (known as a touch screen),
When data is stored in the cloud, the hosting company which means that the user can select items by directly
takes all responsibility for storing the data, managing the interacting with the display on the screen. These are often
data, securing the data and backing up the data, so that integrated into tablet computers and mobile phones.
people or organisations no longer have to be concerned
with this. As the data is stored remotely, it also means that Keyboard
it can be accessed at any time in any place, so people do
not have to be sitting at a specific computer or within an 27
organisation to access that data.

EXAMPLE Figure 2.06 - A Chinese keyboard.

Examples of cloud storage for personal use include: A keyboard consists of a number of buttons which are
used to input text or to control parts of an interface. Its
• OneDrive main limitation is the number of keys available. With a
Roman alphabet, this isn’t too much of a problem because
• Google Drive the alphabet only contains 26 letters and ten digits.
However, some alphabets, such as Arabic or Chinese
• Dropbox contain many more characters and so combinations of
keys have to be used.
• Box
A keyboard can be connected to a computer using a USB
The downside is that it takes longer to access the data as port, by wireless Bluetooth or by other wireless technology.
access times are limited by the bandwidth available to the Keyboards vary in style and shape, and ergonomic
hosting company and other users who may be accessing keyboards are available to provide more comfort and
data on the same servers at the same time. It can also protection for the user from repetitive strain injury (RSI).
be quite costly to store large amounts of data on cloud
storage.

Some cloud storage options allow synchronisation
to a computer, so the cloud acts as a backup to the
data stored on the computer. It also means that when
accessing the data from the allocated computer,
access times will be faster than accessing from cloud
storage.

Cambridge International AS and A level IT

Mouse

A mouse is a pointing device which allows objects to be
selected and manipulated on the screen. The mouse
controls a pointer which is displayed on the screen. When
the mouse is moved, the pointer moves and objects
such as menus can be selected on the screen using one
of the mouse buttons. Like a keyboard, a mouse can be
connected using a USB port, by wireless Bluetooth or by
other wireless technology.

Printer

A printer produces a hard copy (printout) from a

computer usually onto paper. A simplex printer can print

on a single side of paper, whereas a printer with a duplex Figure 2.07 - Modern inkjet plotter.
unit can print on both sides of each sheet of paper.

Some printers include additional functions such as a Speakers
scanner. Speakers are used to provide sound output from a

Laser printer computer. These can be as simple as a pair of stereo

A laser printer negatively charges a cylindrical drum speakers or full surround sound.

which then attracts electrically charged toner (powdered

ink). The toner is then heated so that it melts onto the

paper. TASK

28 Find out the difference between mono sound, stereo
sound, 5.1 surround sound, 6.1 surround sound and 7.1
Inkjet printer surround sound.

Cartridges full of ink in four different colours (black, cyan,
magenta, yellow) are used to ‘squirt’ ink onto the paper to

form the required printout.

Dot matrix printer Camera

Before laser and inkjet printers, dot matrix printers A camera can be used to capture still or moving images
were commonplace. They are a type of impact printer (movies). When connected to the computer, the images
which means that the printout is achieved by hitting or movies can be transferred from the camera to the
the paper and the operation is very noisy. This is done computer’s storage. The images can then be viewed on
by a set of pins being driven onto a ribbon which then screen, manipulated and shared. A digital still camera is
transfers its ink to the paper. The main advantage of optimised for capturing still images but usually has the
dot matrix printers is that they can print on duplicate capability of capturing movies too, whereas a digital
and triplicate paper (carbon copies) due to the impact. video camera is optimised for capturing movies but can
They are also very robust printers and so last for a also capture still images.
long time.

Plotter Webcam

In the 1990s, a plotter used to ‘plot’ lines onto large sheets A webcam is a camera that is connected to the computer
of paper by moving the paper backwards and forwards for the purpose of capturing still or moving images while
and drawing using pens to create vector drawings. Today, using the computer. It will not be as high quality as a
plotters are inkjet printers designed to be used with large dedicated digital camera or digital video camera. It will
sheets of paper, typically A2, A1 and A0. If only black and usually have an integrated microphone for capturing
white printouts are required, then light-emitting diode sound. Its main purpose is for users to engage in online
(LED) plotters are much faster and have cheaper running video chat or video conferences. They can also be used as
costs than inkjet plotters. security cameras.

Chapter 2: Hardware and software

Laser Inkjet Dot matrix Plotter

Typical printing The laser printer is the Standard inkjet Very slow compared The time per page
speed fastest of all printers, printers can usually with other printers. to print is quite slow
with some industrial print around 15–20 because a much larger
Typical models reaching 200 ppm in black and area needs to be
purchase cost pages per minute white, but colour covered.
(ppm) and office speeds are a bit
Typical running printers achieving slower.
cost around 50 ppm.

Colour A laser printer is Inkjet printers are the These used to be Plotters are the most
Quality typically twice the cost cheapest of all printers very cheap, but are expensive type of printer
of an inkjet printer available, but they now more expensive due to their physical size
Typical uses with similar features. vary depending on than an inkjet printer and the need to cope
the features that are because they are not with large sheets of
included. mass produced. paper.

Although toner Inkjet cartridges Very low as the ink The running costs are the
cartridges are more vary in price and ribbon lasts for a long same as inkjet printers,
expensive than inkjet ‘compatible’ versions time. but of course per page
cartridges, they last a can be purchased costs are higher because
lot longer and so the more cheaply than the page sizes are 29
cost per page is less original manufacturer larger. LED plotters have
than other printers. versions. cheaper running costs
than inkjet plotters.

Most are monochrome Almost all inkjet It is very rare to find Plotters can print in
a dot matrix printer colour.
but colour laser printers can print in that uses coloured
ribbons.
printers are available. colour.

The highest quality of A reasonably good Quality is usually Same issues as inkjet
all printers due to the quality, but ink can poor due to the printers, but if pens are
way it melts toner and show through thin bitmapped nature of used then the quality of
attracts it to the page. paper and smudges printing characters. line drawings is high.
can occur.

Letters, bulk printing, Photographs, charts, Invoices or receipts Architectural drawings,
general office and small maps, general requiring duplicate large maps, canvas prints
home printing. office and home or triplicate paper, and signs.
printing. automated teller
machines (ATMs),
point of sale systems,
data logging, hot and
dusty environments.

Table 2.01 - Different types of printer.

Scanner designed to take close-up images of 2D documents. Flat-
bed scanners can capture a full-colour image and save
A scanner is used to capture two dimensional (2D) the image as a file on the computer’s storage. If the image
documents in the form of an image. They perform a contains lots of text, then it is possible to run optical
similar function to a digital camera but are specifically

Cambridge International AS and A level IT

character recognition (OCR) to recognise the text. Some Magnetic ink is used to print numbers at the bottom of
flat-bed scanners include an automatic document feeder checks. The numbers are printed using the MICR E-13B or
(ADF) that enables documents with multiple pages to be CMC-7 font. The ink contains iron oxide which means that
scanned in one operation. it is easily detected when using a magnetic ink character
reader (MICR) and the characters can be understood.
It is important that mistakes aren’t made and so MICR
provides a much better level of accuracy than OCR.

Figure 2.08 - Flat-bed scanner with an ADF. Optical mark reader

An optical mark reader (OMR) detects the marks
that are made on a multiple choice document
such as a multiple choice answer paper for an
examination. A scanner-like device is used to
reflect a beam of light onto the marked sheet and
detect where the marks have been made. Software
is then used to translate the position of the mark
to the information that it represents. OMR devices
are only really suitable for multiple choice
responses as they cannot interpret letters that
form words.

Optical character reader

An optical character reader (OCR) is a device that
30 enables characters on a document to be identified

and understood by the computer as letters, numbers,
characters and words. This isn’t really a device in itself,
but is a scanner combined with software that performs
optical character recognition (also OCR). The picture of the
document is analysed and characters are recognised by
the software and turned into a document so that the text
can be searched or edited.

Magnetic ink character reader

Figure 2.10 - Multiple choice OMR exam paper.

Magnetic ink Barcode reader

Figure 2.09 Checkbook with magnetic ink. A barcode reader is used to detect the width of lines and
gaps that form a barcode. A laser beam is shone onto the
barcode and a photodiode is used to measure the amount
of light that is reflected back. Black lines will not reflect
any light but white gaps will. A barcode represents letters
and numbers which usually identify something, such as
a book or other product. The barcode scanner usually
includes its own hardcoded circuitry so that it can send
the letters and numbers directly to the computer without
the need for additional software.

Chapter 2: Hardware and software

DISCUSSION POINT A standard Blu-ray disc is read only and used to distribute
HD movies. However, it is possible to buy recordable (Blu-
Barcodes are limited in terms of the amount of data that ray) discs that can be written to once and are useful for
can be stored, which is why quick response (QR) codes are archive and backup purposes, or rewritable (Blu-ray) discs
now being used for items of data beyond a string of letters which can be rewritten to and erased making them useful
and numbers. for both backup and data transfer purposes.

Pen drive DISCUSSION POINT 31
A pen drive is a nickname for a USB flash drive. It is a small Find out about the next advancement in optical storage,
data storage device about the size of a thumb which the holographic versatile disc (HVD).
stores data on flash memory and includes an integrated
USB interface. The USB interface means that the flash Memory card
drive is recognisable on all computers with a USB port A memory card is flash memory on a small card. They are
and therefore data can be transported easily between typically used in digital cameras, digital video cameras
computers. Flash memory is very fast and so the limiting and mobile phones. They take up very little space so are
factor is the speed of the USB port. As a flash drive does well suited to fitting into a small device, as well as being
not have any moving parts it is safe to transport, although portable so that data can be transferred to a computer.
its size means that it can be easily lost. It also does not rely There are many different formats of cards, but most
on magnetising and therefore is not susceptible to damage devices favour Secure Digital (SD) and microSD cards.
if it comes in contact with a strong magnetic field. MicroSD cards are only 15 × 11 × 0.7 mm in size.

Portable hard disk drive TASK
Hard disk drives were introduced earlier in this chapter. As Categorise each of the internal and external hardware
well as an internal HDD, it is possible to have an external devices into input, output and storage devices.
HDD. An external HDD can be connected to the computer
using a USB or External Serial Advanced Technology Storage devices
Attachment (eSATA) port. An external HDD can store
a lot more data than a USB flash drive, but it is more Remember
susceptible to damage due to it having moving parts and The main purpose of a storage device is to store data or
its vulnerability to strong magnetic fields. software that can be used by a computer. A storage device
is known as secondary storage, which is non-volatile and
Blu-ray disk drive so data is not lost when the computer is turned off.
A Blu-ray disk is an optical storage medium. It is the same
size and shape as a compact disc (CD) and digital versatile There are many reasons why a user may want to save data
disc (DVD). The Blu-ray disc was introduced because it can to secondary storage:
store HD video and therefore a whole film can be stored
on the Blu-ray disc. A single layer Blu-ray disc can store • when creating a document, a user is likely to want
25 GB of data and a dual-layer Blu-ray disc can store 50 GB
of data. This compares to a DVD which can store 4.7 GB to make changes to that document in the future
of data and a CD which can store 700 MB of data (or 80 and therefore it is necessary to save it to secondary
minutes of audio). storage

A Blu-ray disc drive is required to read data from or • the user may want somebody else to edit or read the
write data to a Blu-ray disc. It uses lasers to read data
that has been written in ‘pits’. A basic Blu-ray disc document and so it will be saved to secondary storage
drive can read data at 4.5 MB/s, whereas a 16× Blu-ray to allow the person to do that
drive can read data at 72 MB/s. This is much slower
than a HDD but the discs are very cheap to purchase • users are likely to want to keep documents for archive
compared with a whole HDD.
purposes so they can be referred to in the future

Cambridge International AS and A level IT

• when using a database, each new record or change Compact Digital versatile Blu-ray
disc (CD) disc (DVD) disc
to a record will be saved to the database in secondary
storage Capacity 700 MB 4.7 GB 25 GB
(single
• the user may want to back up the data so that a spare Original Music Films layer)
purpose
copy is available. HD films

Other reasons for secondary storage include:

• each program will be stored on secondary storage ready

to be loaded into RAM when the program is opened

• the computer will use secondary storage to save a Table 2.02 - Types of optical storage.

virtual memory file which extends the amount of RAM

available, albeit making the virtual part of the memory In addition to distributing music and films, optical storage has

very slow. been a popular medium to distribute software due to the low

Magnetic tape drive cost of each disc, the fact that read-only versions of each disc
exist and the low cost of posting them. Using recordable and
Magnetic tape is used for backing up and archiving data. rewriteable versions of optical discs makes them suitable for
Data is stored serially which means one item after another. backups and archives. It is quicker to restore a single file from
The tape is wound through the tape drive and as it an optical disc backup rather than a tape backup because
winds through data is written to it. The low cost and high the file can be accessed directly rather than having to read
capacity of tapes makes them ideal for backing up and through a whole tape. This also makes optical discs more
archiving data because the data is simply stored in suitable for archived data because files can be found quickly.
a sequential manner. The capacity of optical discs is much less than tapes, which

When retrieving data, it does take a while to find the means they are only suitable for backing up a selection of
32 data that is required because the tape has to be files rather than the whole of secondary storage.

wound to the exact position where the data is Hard disk drive
stored. This makes it unsuitable for everyday use.

Backups and archives are not intended for everyday HDDs were introduced earlier in this chapter. Their principal

use. If data does need to be restored from backup, purpose is to act as the main secondary storage device for

it may take a while but it is at least available when a computer. Data and programs are stored on the HDD so

needed. If the whole of a computer’s secondary that they can be accessed as and when required. External

storage needs to be restored, then this can be done HDDs can also be used to back up data (although this is

by reading the tape sequentially. an expensive way of doing it) or to transfer data to another

Tapes are ideal for backing up the whole of secondary computer. Moving parts within a HDD make it vulnerable to
storage for a computer or server because they can hold damage if dropped.

several terabytes (TB) of data. In 2014, Sony developed a Solid state drive
tape capable of storing 185 TB of data. SSDs were introduced earlier in this chapter. Similar to a

HDD, a SSD can store the data and programs that are used

TASK by a computer. SSDs are faster than HDDs, but also more
expensive. SSDs require less power than a HDD so they are
Find out how the grandfather–father–son backup often used in tablet computers and high-end laptops to
rotation system works using magnetic tapes. How many extend the battery life. Storing the operating system and
tapes would be needed if the monthly backups were programs that are used most on a SSD instead of a HDD
kept for three months at a time? will significantly improve the performance of a computer.

Optical TASK

Optical storage was introduced earlier in this chapter Compare the prices of SSDs and HDDs. Work out an
under the heading Blu-ray. In 2015, there were three main approximate cost per megabyte (MB) for each.
types of optical storage.

Chapter 2: Hardware and software

Hard disk Solid state Cloud Pen Drive
Designed for
Cost of purchase The cheapest cost More expensive per MB Usually a subscription portability and so
Running per MB for everyday than a hard disk (e.g. charge that varies cost per MB varies
cost / power storage (e.g. $0.06 per $0.10 per GB). depending on depending on size.
consumption GB). supplier. Power only required
when in use.
Speed of access Requires constant Does not require Running costs are Portability means that
supply of electricity constant source of included within a they may get damaged
Interoperability when the disk is spinning power as only needed subscription charge. and need replacing.
but if not in use can be when in use.
Typical use temporarily turned off. Depends on whether
Moving parts mean that using USB 2 or USB
it may fail in the future. 3 ports. USB 3 offers
faster data transfer
Depends on SATA Up to 30% faster Depends on than USB 2.
connection used. access speed than broadband Can be connected to
hard disk. bandwidth of user any device with a USB
and that offered by port.
supplier.
For transferring data
If internal, can only If internal, can only Can log on from any between devices.
be used in device be used in device device including
connected to unless connected to unless mobile devices.
moved permanently, moved permanently,
but if external can be but if external can be 33
used in any device with used in any device
a USB port. with a USB port.

In a desktop computer. Laptop and tablet Collaboration with
computers. other users, backups,
sharing of files and
general storage.

Table 2.03 - Comparing storage devices.

TASK Input Processing Output
Complete a table similar to that shown in Table 2.03 for
memory cards, magnetic tape drives and Blu-ray disc drives. Storage

Input and output devices Figure 2.11 - IPOS diagram.
Data that has been stored can also be processed and then
TIP output from the computer.
Input devices allow data to be sent to a computer (e.g.
keyboard). Output devices allow the communication of EXAMPLE
data/information from a computer (e.g. monitor). When
data is input into a computer, it is processed and then Multiple choice answers from an examination are
either output from the computer or stored for later use as scanned using an OMR and the answers for each
shown in Figure 2.11 and is known as an input–process– student are stored. Once all the answers have been
output–storage (IPOS) diagram.

Cambridge International AS and A level IT

scanned, the stored answers are checked and the It may be important to know who or what needs the
marks calculated for each student. The marks are device and you should refer to the school in your answer:
printed out.
• It’s important to know the data is being backed
Figure 2.12 shows this process. up from servers because this tells you that a large
capacity will be required.
Multiple choice Answers stored Answers checked Results Printed
answers from (Process) (Process) (Process) • Knowing the data is a backup means you know
OMR (Input) immediate access to the data is not essential.

Storage Results printed • The fact that data has to be kept off site is essential
out on printer because this means the device used must be able
to be moved away from the school.
Figure 2.12 - Multiple choice IPOS diagram.
Here is an example of how the question could be
Evaluate different input, storage or output answered:
devices for a given task
Answer: An external HDD is lightweight and
Based on your understanding of a variety of input, storage portable meaning that it will be easy for the school
and output devices, you will now need to evaluate the to take the backup off site.
suitability of a device for a given task. When evaluating,
you need to consider both the reasons why the device As the HDD contains moving parts, the heads could
would be suitable and also the reasons why the device crash causing data to be lost when transporting it off site.
would not be suitable. You should then make a conclusion.
34 In real life, this is what you would do to advise somebody The HDD will have a reasonably large capacity which
which device they should use. could be around 8TB. This may be enough to store all
of the data from a small school’s server, but a larger
You could also be asked to evaluate the use of a given school would require more than one external HDD.
device for a given task. In this situation, you would only
need to give positive reasons why that device would be As it is a school, some of the data being backed up is
suitable. likely to be personal data which must be kept secure
according to the Data Protection Act. When taking the
When analysing and evaluating, you should consider data off site, it is possible that it could be lost or stolen
which features of the device make it suitable for the due to its size. However, encryption could be used to
specific task that has been presented to you. To do this, make the data unreadable if it was lost or stolen.
you will need to identify the important aspects of the task
and relate the useful features of the device to each aspect Storing the backup on a single external HDD means
of the task. that it would have to come back to the school each
day, which defeats the object of keeping it off site.
EXAMPLE Therefore, several external HDDs would be required
to ensure that there is always a backup off site and
Question: A school needs to back up data from its this could become very expensive.
servers every day and keep the backup data off site.
Evaluate the use of an external hard disc drive for In conclusion, although the external HDD can be taken
this task. off site, I would suggest that it is not suitable due to the
cost of multiple drives and because the capacity may
The first thing you should do is identify the important not be sufficient. Using tapes would be more cost-
aspects of the scenario that will give you clues as to effective and would overcome the cost issue.
whether the external HDD is suitable or not:
Note how the answer makes reference to the
A school needs to back up data from its servers every scenario and links to the features of an external HDD.
day and keep the backup data off site. Evaluate the
use of an external hard drive for this task. TASK
Analyse and discuss the use of the following devices for
each scenario given. Remember that you only need to
give positive reasons.

Chapter 2: Hardware and software

Device Scenario System software

Plotter An architect is preparing drawings for a new house Programs that are designed to maintain or operate the
that is to be built. Different colours will be used to computer system are known as system software. The
identify electricity, water and gas services. software that operates the computer hardware is known
as the operating system. Programs that are used to
Digital An employee travels regularly as part of maintain a computer system (e.g. anti-malware software)
camera her job. She is required to keep a record of are known as utility software.
expenses and to email copies of all receipts to
the finance department. Operating systems

Pen A church records the preacher’s talk each week. Remember
drive The computer that is used is not connected to the An operating system manages the hardware within a
internet, but the talk needs to be uploaded to a computer system. When a computer is turned on and
website after the church service. after the Basic Input/Output System (BIOS) has loaded,
the operating system is the first piece of software that will
Turn your answers into evaluations by also looking at load. It sits between hardware and applications software
reasons why each device would not be suitable for each and manages any communication between the two.
task and give a conclusion.

QUESTIONS Application 35

1 Define the term hardware. Operating system
2 Describe the role of the central processing unit (CPU).
3 Describe the role of a graphics card. Hardware
4 Contrast random access memory (RAM) and a
Figure 2.13 - Operating system.
storage device. An operating system manages hardware by carrying out
5 Compare and contrast a digital camera to a scanner. tasks such as:
6 Evaluate the suitability of an optical mark reader
• allocating memory to software
(OMR) and an optical character reader (OCR) for • sending data and instructions to output devices
marking exam papers. • responding to input devices such as when a key is pressed
• opening and closing files on storage devices
2.02 System, application and user • giving each running task a fair share of processor time
interface • sending error messages or status messages to

KEY TERMS applications or users

Software: programs which give instructions to the computer • dealing with user logons and security.
User interface: communication between the user and the
computer system TASK
Microsoft Windows is an example of an operating system.
TIP Find at least two other operating systems used by
Software is also known as programs, such as word desktop computers and at least three operating systems
processing, spreadsheet, anti-malware or operating used by mobile phones or tablets.
system. Each program consists of programming code
which gives instructions to the computer in order to
carry out a task. The code that is passed to the hardware
is in binary format which consists of instructions in the
form of lots of ones and zeros (e.g. 101011101110).

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Device drivers be distributed to resellers, customers and individual
computers. As it is in an executable format, it can only
While the operating system can manage the general run on operating systems for which the compiler has
instructions to deal with hardware such as displaying translated it. For example, programs that have been
graphics on a screen, it requires the use of device drivers to compiled for Windows will not work on Linux unless
deal with specific makes and models of hardware. A device they are compiled again for Linux. The same situation
driver is the software that comes with an external hardware exists with mobile phone and tablet operating systems.
component and sends customised instructions to that
specific component. By using common device drivers, Program file (source file)
software applications are able to issue generic commands
such as ‘print’ to the operating system without having to
know the different instructions required for every different
make and model of external hardware components.

Application Compiler

Operating system

Executable file (object file)

36

Device driver

Execution
by CPU

Hardware Figure 2.15 - Compiler diagram.

Figure 2.14 - Device driver. Interpreters
Interpreters also translate a program written in a high-
Utilities level programming language into machine code, but
Utilities are part of system software. They are designed to use a different method. Instead of translating the whole
perform functions which maintain the computer system. source code at once, it is translated one line at a time.
Utilities are discussed later in this chapter. This can be less efficient than a compiler because
it takes time to do the translating as the program is
Compilers being executed and also because statements within
A compiler translates a program written in a high-level programming loops (e.g. FOR, REPEAT, WHILE) have to be
programming language into machine code which a analysed each time round.
computer can understand. The file containing the
machine code is known as an executable file because it Interpreters are often used to translate macros or
can be executed by the processor. It can also be referred application-based script languages (e.g. Visual Basic
to as the object file. The original high-level programming for Applications), which can be particularly useful
language file is known as the source file. when a document needs to be opened on a variety of
operating systems. Interpreters are also used when
When a program is compiled, the whole source code is testing programs so that parts of the program can
translated into the executable file at once and can then be executed without having to compile the whole
program.

Chapter 2: Hardware and software

DISCUSSION POINT Not all modules are always needed and a linker is able to
select which modules will form part of the executable file.
Java uses both a compiler and an interpreter. The original
Java source code (files with a .java extension) is compiled Application software
into Java bytecode (files with a .class extension) which is
an intermediate code. In order that the Java program can Programs that are intended for productivity or to carry
work on any operating system, a Java Virtual Machine out a task for the user are known as application software.
installed on the computer is used to interpret the bytecode Examples include word processor, games, web browser
at the time of execution. and graphics software. On a mobile phone or tablet, this
type of software is usually referred to as an app.
Java interpreter
for Mac OS You are likely to be asked to analyse or evaluate the use of a
particular piece of software for a given task. You will need to
Java Compiler Java Java interpreter look at the details of the task and relate appropriate features
source code bytecode for Windows of the software that are likely to help solve parts of the
task. You will also need to consider whether there are other
Java interpreter software options available, consider how they could be used
for Linux to complete the task and then provide a conclusion.

Figure 2.16 - Java diagram. When making reference to software always use the name
of the type of software (e.g. word processor) rather than a
Linkers trade name (e.g. Microsoft Word). 37

Computer programs often consist of several modules Word processing
(parts) of programming code. Each module carries out a
specified task within the program. Each module will have TIP
been compiled into a separate object file. The function The function of a word processor is to primarily process words.
of a linker (also known as a link editor) is to combine the
object files together to form a single executable file. In It is therefore appropriate for tasks such as:
addition to the modules used, the program may make
reference to a common library. A common library contains • writing a letter
code for common tasks that can be used in more than • producing a report
one program, such as mathematical functions, memory • producing coursework
management, open and save dialogues, progress bars • creating a menu
and input/output. The linker is able to link modules from a • mail merging
library file into the executable file, too. • writing a book.

Source Source Source Source Features of word processing software include:
file file file file
• tables
Compiler • headers and footers
• footnotes and endnotes
Object Object Object Object • sections
file file file file • formatting text
• styles
Runtime Linker Executable • spellchecker
library program • bullets and automatic numbering
• automatic contents page
Figure 2.17 - Linker diagram. • tracking changes
• frames for images
• text alignment

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• text wrap Spreadsheet
• indentation and tabs.
ABC
TASK
If you are unfamiliar with any of the features above, 1 Starting distance Ending distance Distance travelled
then find out about them and try using them. A website
that may help you with this is www.teach-ict.com/ 2 20,035 19,829 =A2–B2
videohome.htm or the official Microsoft video tutorials
on Microsoft’s Office support site. 3

EXAMPLE Figure 2.18 - Spreadsheet formula.

Question: Give reasons for the use of word processing ABC
software for creating a menu for a restaurant.
Think of the features you would expect to find on a 1 Starting distance Ending distance Distance travelled
menu and how it might be produced. Then relate
them to the features of word processing software 2 20,035 19,829 206
that could be used to create the menu.
Answer: Alignment could be used to centre the 3
name of the restaurant and the word ‘Menu’ at the
38 top of the page. Figure 2.19 - Spreadsheet calculation.
The name of the restaurant could be formatted
using a different font in a larger size to the rest of the Spreadsheet software is used mainly for performing
text and in a different colour. calculations and modelling. Spreadsheets are often used
Frames could be used to include images of each for financial and statistical information. Spreadsheets
dish on the menu. work on the basis of input–process–output whereby
Text wrap could be used so that text wraps around data is input, then formulae and functions process that
the images of each dish. data to generate an output. When input data changes,
Automated numbering could be used to give each the output data automatically changes because the
dish a number that can be used when ordering. formulae and functions are automatically recalculated.
The spellchecker could be used to ensure that all This allows users to experiment with values and ask
descriptions of the dishes have been spelt correctly. ‘What-if’ questions such as ‘What will happen if we try to
Footnotes could be used to identify dishes which sell another 10 000 cars this month?’
contain nuts or are vegetarian options.
Styles could be used so that subheadings are kept Spreadsheets contain cells which form the intersection
consistent by applying a style rather than manually of rows and columns. In Figure 2.19, cell C2 contains the
formatting each subheading. value 206.

TASK TASK
Give reasons for the use of word processing software for
writing a book. CD 2.01 Lease pricing model
Open CD 2.01 Lease pricing model.xlsx and
experiment with changing the input values in the
yellow cells in the Pricing Model spreadsheet. This
spreadsheet calculates the total cost of a hire car
based upon different variables including the list price
and carbon dioxide (CO2) emissions of the vehicle.
1 Watch what happens to the total cost of the lease

when you adjust the input values.
2 Compose a list of at least three ‘What-if’ questions

that could be asked using this spreadsheet model.

You will learn more about spreadsheets in Chapter 8.

Chapter 2: Hardware and software

Database management systems • cloning parts of an image
• softening (blurring) and sharpening an image.
Remember
Database management systems (DBMS) are used for Features for vector graphics manipulation software can
viewing and editing data within a database. A database is include:
a structured collection of data in the form of tables which
are related to each other. For example, an invoicing • filling a shape with colour
database would include tables for customer, products, • changing features of the border of a shape such as
orders and order-lines (orders for each product).
thickness and colour
A DBMS can provide features including:
• combining shapes together into a group
• data entry screens / forms for inputting data • moving a shape or group of shapes
• filters and queries for selecting data that meets specified • resizing a shape or group of shapes
• aligning objects.
criteria
Using graphics manipulation software requires a lot of skill
• reports for displaying information in an easily readable and advanced features are usually more appropriate for
serious artists.
format
You will learn more about graphics manipulation in
• graphs for analysing data Chapter 16.
• security features so that users can only access the parts
TASK
of the database they have been authorised to access Investigate the features available in Paint.NET, IrfanView
and CorelDRAW.
• relationships to link related tables.
39
You will learn more about databases in Chapter 9.

Graphics manipulation software

TIP Photo editing software
As its name suggests, graphics manipulation software is
designed to manipulate graphics. This can be either bitmap Remember
graphics or vector graphics. Photo editing software is a specific type of graphics
manipulation software that is focused on editing
The features included in graphics manipulation software photographs. This can be used by professional
vary depending upon the complexity of the software. photographers and enthusiasts to enhance photographs
or by people at home to make minor changes.
Features for both bitmap and graphics manipulation
software can include: Features of photo editing software include:

• drawing shapes • cropping parts of the photo
• changing the canvas size • adjusting the brightness or contrast
• resizing the image • resizing the canvas
• adding layers • removing red eye
• adding text to an image • changing the colour balance
• selecting a colour based on picking an existing colour. • cloning parts of the photo
• identifying common areas of an image (e.g. background)
Features for bitmap graphics manipulation software can
include: using a ‘magic wand’ tool

• filling an area with a colour • applying effects such as black and white or sepia
• moving part of the image • softening (blurring) and sharpening a photo.
• resizing part of the image
• erasing parts of an image Photo editing software requires a large amount of RAM
and complex operations can use up a lot of processing
time.

Cambridge International AS and A level IT

Video editing software same time. During an audio conference it can be difficult to

know whose turn it is to speak. Video conferencing expands

Remember upon audio conferencing by including real-time video of the
When videos are recorded, they are known as ‘raw’ video people involved in the conference.

files (footage). There are many enhancements that can be Email clients provide users with a larger range of
made to a raw video file and this is where video editing features than webmail and enable emails to be read and
software comes in useful. composed while offline. This can be useful when no fixed

Features of video editing software include: internet connection is available and 3G/4G coverage is
poor or non-existent.

• importing or capturing raw video Features of email clients include:
• clipping the beginning and end of a video
• address book of contacts
• clipping sections within a video
• ability to send and receive emails
• adding titles to the beginning or credits at the end
• signatures
• overlaying videos with text or images • prioritising of emails
• speeding up or slowing down footage • delaying delivery of emails
• rotating footage • delivery and read receipts
• using more than one video track • rules that can be applied to email messages (e.g. moving
• transitioning between clips (e.g. fade)
messages that contain a specific subject to a specific
• add backing music, narration or other sound folder)
• using picture-in-picture to show two video clips at once.
• using more than one email account at once
Video editing software does have some downsides and
these include: • adding attachments to messages
• digital signatures and encrypted messages
40

• using up a lot of processing time • integration with a calendar

• requiring a large amount of RAM • inviting contacts to a meeting in the calendar and

• importing raw video files can take a long time receiving responses.

• encoding the final video takes a very long time.

You will learn more about video editing in Chapter 10. TASK
Communications software
If you are unfamiliar with any of the features above, then
find out more about them. There are several freeware
email clients that you could download and use.

Remember Web authoring software
Communications software can cover a range of tasks
including instant messaging, audio conferencing, video Remember
conferencing and email. Web authoring software is used for the creation and
editing of websites.
Instant messaging software allows a user to communicate
with another user by sending text-based messages which There are now many online content management systems
are instantly sent and received. This can be a slow form of and other tools that are used to create and update
communication because of the need for typing, but some websites, but some web developers sometimes prefer to
people prefer it to having a real conversation. use offline web authoring software such as Dreamweaver.

Audio conferencing allows users to speak and listen to Web authoring software can be very complex to use
each other in a similar way to a telephone call. The main because of the vast number of configurations available
difference is that more than two people can be included for web pages, which is why using an online tool like
in the conference. This is usually achieved with voice over www.wix.com enables people with little experience of
internet protocol (VOIP). A popular example is Skype. Making websites to create a site quickly, although it can be difficult
conference calls over the internet is usually free of charge
but it does require every participant to be logged on at the

Chapter 2: Hardware and software

to customise it to exact requirements. Web authoring • wind speed 41
software gives the most flexibility and websites can be • distance (measured by lasers)
configured exactly as required. • pH (acid/alkaline) levels.

Features of web authoring software include: Control software will control devices such as:

• common navigation bar • lights
• ability to publish individual files or sites to a web server • motors (e.g. to make windscreen wipers move)
• preview of web pages • speakers/sirens
• viewing and editing in either what you see is what you • heating.

get (WYSIWYG) view or Hypertext Markup Language Apps
(HTML) code view or a mixture of both An app is another name for a program. It is a piece of
software that can run on a desktop computer, over the
• adding basic HTML features such as tables, horizontal internet, on a tablet computer or on a mobile phone.
The most common reference to ‘apps’ is when referring
lines and headings to software that is designed to work on mobile devices
such as tablets or mobile phones. In this case, apps are
• management of a web page’s metadata optimised to work with touch screen interfaces and
• designing templates that can be applied to all pages smaller screens. They will provide essential features
• interactive features such as interactive buttons that can be carried out using the limited interface of
• forms and form fields mobile devices, but often lack more complex features
• validation of form fields. due to the need for more processing power or
accurate input devices such as a mouse and
Control and measuring software keyboard.

Remember Apps are also available over the internet and usually exist
Control software is used for controlling devices that are within web pages. For example, webmail is an app that
not part of the computer system. Measuring software is allows a user to manage their emails. Other examples
used to measure values in the real world. include online games, online office software (e.g. Office
365), content management systems, online banking and
EXAMPLE online shopping.

An automated house would require control software Applets
to turn lights on and off, open a garage door, turn An applet is a small program that is designed to carry out a
on the heating, open blinds and sound a burglar specific task. An applet cannot run on its own but must be
alarm. The measuring aspect of the software would executed from within another piece of software. Applets
measure the level of light and time of day and turn are often known as add-ins, add-ons or extensions. They
on the lights when appropriate. It would also detect can carry out additional tasks that the original software is
whether security sensors were triggered before not capable of doing or they can simplify tasks within the
sounding the burglar alarm. Heating would only be original software.
turned on based on the measurement of the current
temperature. TASK
Explore some of the extensions available to Google
Control and measuring software is used in a wide variety Chrome and add-ins available to Microsoft Excel.
of situations including automated features of cars (e.g.
automatic windscreen wipers), science experiments, Evaluate application software for a given
weather stations, pollution management and traffic lights. task

Measuring software will measure values from sensors Based on your understanding of a variety of software
including: applications, you will now need to evaluate the

• pressure (amount of pressure applied)
• moisture
• temperature

Cambridge International AS and A level IT

suitability of a software application for a given task. TASK
When evaluating, you need to consider both the reasons A supermarket needs to decide how best to use
why the application would be suitable and also the the space within the shop. More space should be
reasons why the application would not be suitable. You allocated to profitable items. Give reasons for the use of
should then make a conclusion. In real life, this is what spreadsheet software to assist with deciding how much
you would do to advise somebody which application space to allocate to each type of product.
they should use.
EXAMPLE
You could also be asked to give reasons for the use of
a given application for a given task. In this situation, Introduction: A warehouse company needs to
you would only need to give positive reasons why that keep accurate records of how many of each product is
application would be suitable. currently in stock and to where each product has been
delivered. It also needs to know when new stock is due to
When analysing and evaluating, you should consider arrive and ensure that stock levels do not fall too low.
which features of the application make it suitable for the
specific task that has been presented to you. To do this, Question: Evaluate the use of a database
you will need to identify the important aspects of the task management system (DBMS) for this task.
and relate the useful features of the application to each
aspect of the task. Start by identifying the important parts of the
question that you will relate to in your answer.
EXAMPLE These should include warehouse, records, products,
stock and stock levels. Then consider what data
Question: Evaluate and discuss the use might be used in this database and relate features
42 of spreadsheet software for deciding what the of a DBMS to how that data might be used. You
should also consider the problems with using a
best tariff is for a customer to use for a mobile DBMS or other software that would be appropriate.
phone.
Answer: A DBMS will be able to relate data stored
Start by identifying the important parts of the in tables for products, deliveries, destinations and
question that you will relate to in your answer. sources. For example, a foreign key of ProductID in
These should include tariff, customer and mobile the delivery table could relate to a primary key of
phone. Then consider what data might be used ProductID in the product table.
in this spreadsheet model and relate features of a
spreadsheet to that data. A query could be created in a DBMS to find all
the stock where stock levels are low so that more
Answer: Spreadsheet software will enable the stock can be ordered. This would be achieved by
customer to experiment with different variables using criteria to compare the current stock level
(inputs), such as the purchase cost of the mobile with a field that stores the minimum stock level
phone, number of minutes they normally use and that should be maintained. If the current stock
the amount of data needed. level falls below the minimum stock level, then
the product will be included in a re-order query.
Formulae and functions can be used to calculate
each tariff, including the total cost over the period A DBMS could produce graphs to show how much
of the contract. stock has been delivered by the warehouse to each
destination. For each record in the destination
Graphs could be used to compare the cost of table, the number of products that have been
buying a mobile phone up front with a SIM-only delivered to that destination would be counted.
tariff and buying a tariff which includes a mobile
phone. However, spreadsheets can also be used to
create graphs of the stock and the graphs can
A separate worksheet can be used to store a table be customised in more detail when using a
of tariffs and another worksheet for the customer spreadsheet such as deciding on axis
interface.

Chapter 2: Hardware and software

titles, grouping destinations based on their Different types of user interface
geographical location and choosing the intervals to
display on axes. An interface is the boundary between two systems. A
user interface is the boundary between the user and
Databases can be very complex to set up whereas a the computer system. A user interface represents the
spreadsheet could be set up quickly with worksheets communication between a user and the computer system.
for products, destinations and deliveries. Databases This communication can take many forms.
require tables, field types, field lengths, primary keys,
foreign keys, relationships, queries and reports all to Command line interface
be set up following a very clearly defined structure. A command line interface (CLI) allows a user to enter text
commands to which the computer system will respond.
Conclusion: Although the spreadsheet would The computer system will respond by producing results in
be simpler to set up, it would not be able to easily a text format.
manage the complex relationships needed for stock
control and deliveries and so a DBMS would be EXAMPLE
appropriate for the warehouse in this case.

TASK

Give reasons for the use of the following applications for
each scenario given. Remember that you only need to
give positive reasons.

Application Scenario 43
Word processor
A charity sends out monthly Figure 2.20 - Command line interface.
Web authoring newsletters. They require a
software standard layout that will be In this example, the user has changed the directory
used every month and they (folder) to the logs directory (‘cd logs’). Then the user has
Video editing would like each newsletter to be requested a listing of the directory (‘dir’). Finally the user
software addressed personally to their copies the file directx.log to the root directory of the f
supporters. drive (‘copy directx.log f:\’). The user gets a confirmation
message that one file has been copied. The only prompt
A primary school wants to create that the user gets is information about which directory is
a website that can be updated currently active (‘C:\Windows\Logs>‘)
regularly. It must include a
navigation bar with links to each CLIs use very little memory so they are useful in old systems
page and a contact form, as well or for maintenance of very small systems/devices (e.g. engine
as general information about the management systems). They are also useful for technical
school. users who need to carry out complex operations which
cannot be performed using more user-friendly interfaces.
A church records the preacher’s However, CLIs can be difficult to learn and use because users
talk each week including the video. have to learn and remember all the commands, and errors
There are three cameras used in are easily made when entering those commands.
total plus a microphone for the
preacher.

Turn your answers into evaluations by also looking at
reasons why each application would not be suitable for
each task and giving a conclusion.

Cambridge International AS and A level IT

Graphical user interface GUIs are intuitive to use which means they are easy to
learn because commands are represented by pictures and
File Edit View Window Help Ctrl+O 26 / 29 menus provide options that can be selected. However,
Open... they can be restrictive for some technical users who need
Open From Acrobat.com... Ctrl+S to carry out unusual tasks.
Shift+Ctrl+S
Create PDF Online... Dialogue interface
A dialogue interface refers to using the spoken word to
Save communicate with a computer system. A user can give
Save As... commands using their voice and the computer system
can respond by carrying out an action or with further
Figure 2.21 - Graphical user interface. information using a synthesised voice.

The most common type of interface that we use is Give me directions
a graphical user interface (GUI). GUIs are found on to the Taj Mahal
desktop computers, tablet computers, mobile phones,
televisions, set-top boxes, photocopiers and some in-car
entertainment systems.

GUIs can include some or all of the elements shown in
Table 2.04.

Windows An area of the screen devoted to a

specific task, for example a software

application, a file within a software

application or a print dialog box.

44 Icons An image that is used to represent a

program, file or task. The icon can be

selected to open the program, file or

task.

Menus Menus are words on the screen which
represent a list of options that can be
expanded into further sub-menus. Figure 2.22 - Dialogue interface.

Pointers This is the method of representing
movement from a pointing device such
as a mouse or the human finger on a Dialogue interfaces are very popular with mobile devices,
touch screen. The pointer is also used including mobile phones and in-car entertainment
to select and manipulate objects on the systems. Some cars will accept commands such as
screen. ‘Temperature 20’ or ‘Call John Smith at home’. Mobile
phones will accept commands and questions such as
Table 2.04 - Graphical user interface elements. ‘What is the time in Islamabad?’ or ‘Give me directions
to get home’. Some automated telephone systems will
The acronym WIMP is commonly used to remember these recognise voice, too, so that the user doesn’t have to use
elements. the dial pad to input information.

Complex GUIs require a lot of memory to operate, but A big advantage of dialogue interfaces is that no hands
simpler GUIs can be used where memory is limited. are required, which makes them suitable for use in cars
Although CLIs don’t require much memory, simple GUIs or when holding a telephone. In many circumstances,
can be used instead of a CLI in small systems such as words can be spoken by a user more quickly than a user
embedded systems. It is commonplace to find simple can type them. There is no need for a physical interface
web-based GUIs for the maintenance of devices such as with dialogue interfaces , so they are suitable for systems
routers, switches and printers. such as home automation where voice commands can be
given from anywhere to control equipment such as lights,