1
Generic application software
Software Software refers to computer programs. A program is a sequence of instructions that tells the computer’s processor what to do. There are two types of software: • system software • application software. System software: manages the computer hardware provides a uniform environment for application programs to run performs housekeeping and monitoring tasks.
• • •
Application software: allows the user to do useful tasks with the computer such as playing games, writing a letter or monitoring hospital patients • is often supplied as a package • can be generic (off-the-shelf) and is general purpose • can be bespoke, where it is custom-written for a specific task.
•
Application programs Application programs commonly have facilities for: • working in a graphical user interface (GUI) • managing data files and working on multiple files • navigating through the work and changing the ‘zoom level’ • importing files and inserting embedded objects • creating and editing drawings • formatting text and graphics and editing content using insertion, deletion, cut-and-paste, copyand-paste and find-and-replace and Undo and Redo commands • language checking • saving and using templates • viewing a file as it will be printed (WYSIWYG) • creating macros and assigning them to buttons and images • hyperlinking • exporting files in other formats • printing files.
Generic application programs You may be asked to justify your choice of a type of generic application software (no brand names) for a particular purpose. For the particular features of each type of software, refer to the coursebook, especially if you do not have practical experience of it.
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Generic Application software
General use of software
desktop publishing (DTP)
publications with complex layout, e.g. posters, newsletters and magazines
word processing
text-intensive material, e.g. letters, business/legal documents, and mail merges
spreadsheet
repeatable financial, scientific and engineering calculations, mathematical modelling and simple databases
database management system (DBMS)
input, storage and retrieval of records to provide useful information on screen and in printed reports
communication
fax, telephony, video-conferencing, email and instant messaging web authoring, for producing HTML and scripting code for interactive web pages
web browser
for interactively accessing information in the form of text and other media from remote web servers
search engine
a web application for finding information available on Internet servers
graphics
drawing and editing images, both bitmap and vector
computer-aided design (CAD)
for drawing product designs
computer-aided manufacture (CAM)
for manufacturing products from CAD designs
multimedia authoring
producing multimedia ‘movie files’ for animated advertisements and games within web pages or presentations, whole websites, or cinema films
presentation
for creating slideshows (successions of multimedia pages), or multimedia or printed posters
data-logging
for recording data automatically for scientific, engineering and statistical purposes
programming
writing, compiling and debugging computer programs
Customising generic application programs Off-the-shelf generic application programs are readily available, relatively cheap and well tested. They can be customised to the purchaser’s requirements by: • hiding the standard menus and toolbars • creating new menus or toolbars with just the essential requirements • making cosmetic changes to the colour scheme and logo • creating macros run by toolbar buttons or keyboard shortcuts. A macro is program code recorded automatically or written in a scripting language to improve access to existing commands or to create new ones.
Bespoke software Bespoke software (custom-written) is software specially written to suit the needs of a particular customer. It is often very efficient because it does exactly what is required, is easy to learn and has good customer support and maintenance.
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Comparing off-the-shelf with bespoke software Off-the-shelf software has a number of advantages and disadvantages relative to bespoke software.
Off-the-shelf software’s advantages
Off-the-shelf software’s disadvantages
it is immediately available
it may be overly complex and difficult to learn
it is usually much cheaper to buy
it may be a compromise between the requirements of different types of users
it may have many powerful features developed over many years
an organisation may be forced to adapt its business procedures to the software
if it belongs to a suite, it is likely to be able to exchange data and files easily with other programs in the suite
errors may not be fixed rapidly
it is well tested by previous users there is support available from experienced trainers and user groups
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1
Generic application software
1
What does it mean to ‘import’ and ‘export’ a data file?
2
What is bespoke software and what are its advantages and disadvantages compared to generic application software?
3
Connect the task on the left to the most appropriate type of software on the right. Task
Application software
a
finding information for a report
i
word processor
b
creating a web page
ii
desktop publisher
c
creating a science display
iii
spreadsheet
d
recording a DVD collection
iv
database
e
writing to a friend in India
v
email client
f
keeping up with the news
vi
web authoring software
g
producing a club newsletter
vii
web browser
h
writing a letter
viii
search engine
i
designing a new kitchen
ix
graphics editor
j
removing red-eye from a photo
x
CAD software
k
capturing weather data
xi
presentation software
l
managing a school’s records
xii
data-logging software
4
What is the purpose of data-logging software?
5
What is a graphical user interface?
6
Most computers run a spreadsheet application. What is a spreadsheet? Describe one situation where you have used a spreadsheet.
7
Computer-aided design (CAD) is one of the most widely used commercial applications of computer graphics. a Name two areas in which CAD could be used. b Give three features you might expect a CAD program to contain.
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8
The IT department encourages pupils producing the school magazine to use the DTP software provided on the computer network. The network has a colour laser printer attached to it. a Give two extra items of hardware the IT department could buy to help produce a better school magazine. State what each of these two items of hardware could be used for in the production of the school magazine. b When producing the school magazine pupils use an online dictionary and an online thesaurus provided by the DTP software. Explain what each facility is used for. c State four facilities of the DTP package that could be used to produce a poster.
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1
Generic application software
Below each answer there is a page reference for the coursebook. This is there to help you focus your revision. If you find that you get an answer wrong, you can use this guide to return to the coursebook to revise the areas that need some extra attention. Please note these are example answers only and do not represent the only possible answers. 1
When you ‘export’ a data file, you save the data to a format that can be read by another type of program. When you ‘import’ a data file, you read a file that was created by a different program. For example, you can import a spreadsheet file into a database program. See ‘Importing and exporting data files’ on page 4.
2
Bespoke software is software specifically written for a customer. It should exactly match the needs of the customer and therefore operate more efficiently for the customer’s specific requirements than generic software. It is likely to be more expensive to develop and not as extensively tested. See ‘Bespoke software’ on page 25.
3
The contents of the ‘Task’ column have been moved to match the application software. Task
Application software
h writing a letter
i
word processor
g producing a club newsletter
ii
desktop publisher
d recording a DVD collection
iii
spreadsheet
l
iv
database
e writing to a friend in India
v
email client
b creating a web page
vi
web authoring software
f
vii
web browser
a finding information for a report
viii
search engine
j
removing red-eye from a photo
ix
graphics editor
i
designing a new kitchen
x
CAD software
c creating a science display
xi
presentation software
k capturing weather data
xii
data-logging software
managing a school’s records
keeping up with the news
See Chapter 1 Generic application software. 4
Data-logging software automatically collects data from sensors, usually at regular time intervals. The data can then be analysed or used to control applications. See ‘Data-logging’ on page 21.
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1
5
A graphical user interface enables the user to use windows, icons, menus and a pointing device to control software. See ‘Graphical user interface’ on page 4.
6
A spreadsheet is an application that organises data in rows and columns and enables the user to apply formulae to the data. I have used a spreadsheet to model the financial transactions for a club – I enter the money received and spent and the spreadsheet software automatically updates the balance. See ‘Spreadsheets’ on page 7.
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a b
CAD can be used in architecture and in product design. I would expect a CAD program to be able to create 3-D drawings using vector graphics, to rotate or walk through drawings and to calculate areas and volumes of designs. See ‘CAD/CAM programs’ on page 17.
8
a
b c
The IT department could buy a scanner to enable the magazine production team to scan photos and other items that exist only in hard copy. They could also buy a digital camera for the creation of new images. An online dictionary is used to check that the words used in the magazine exist (i.e. to check spelling). An online thesaurus is used to offer alternative words that mean the same. The DTP package could be used to produce a poster using the facilities to import images, flow text around images, format text and rotate text and images. See ‘Word processing and desktop publishing programs’ on page 4.
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2
Data
Data and information Data are the raw facts and figures that we give to a computer as input. Data lack sufficient context and processing to have meaning. When data are processed to have context and meaning, and to search, sort and make calculations, they become known as ‘information’.
Data collection and preparation Data may need preparation after collection and before they are used as an input, to ensure that they are in the correct format. Data are encoded to summarise them, so that they are quicker to enter, with fewer errors, occupy less memory and backing storage, and are quicker to process. Data sometimes need to be prepared so that they have a uniform format suitable for input into a computer.
Analogue-to-digital converters and digital-to-analogue converters An analogue input signal needs to be converted into digital data. This is done with an analogue-todigital converter (ADC). This process is known as digitisation. Digital output signals often need conversion to analogue signals in order to provide an output. This is done with a digital-to-analogue converter (DAC). ADC and DAC devices can be found in a computer’s sound card.
Data capture and checking Data capture is when data actually enters the computer. This happens after data collection and data preparation. Data capture may be: • manual • automatic. Inaccurate data are of little value, so their accuracy is checked by validation and verification. Data validation
A validation check prevents the input of a data item if it is not sensible and reasonable. When this is the case, an error message is displayed. Types of validation check include: • type • range • limit • length • character
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• • • •
format or picture presence consistency check digit.
Data verification
Sometimes an inaccurate data item can pass validation checks due to a copying error. Verification is a way of double-checking to ensure that data remain accurate when they are copied. Common checks are: • visual • double entry • parity bit.
File organisation and manipulation • a record is a set of data usually displayed in a row of a table: – a data field holds a specific type of data about a characteristic of the items recorded, usually
•
displayed in a column of a table – a record key field holds a unique identifier for each record – a set of records are stored together as a data file records within files can be organised in different ways: – a serial file – a sequential file – a direct access file.
File maintenance File maintenance is the processing of a file that is not part of routine transaction processing, or updating a main file using a transaction file. Maintenance involves: • inserting a record, e.g. a new record for a new client • deleting a record, e.g. removing the record of a client who ends their relationship with the organisation • updating (amending or editing) a record, e.g. altering the record of a client who changes their address. This usually involves rewriting the whole file for a sequential file, but not for a direct access file.
Data types Different data types are identified so that a computer can store and process the data appropriately. Data types include: • string (or text) • number (numeric): – integer – real (or decimal) • currency • date/time • Boolean (or Yes/No). Data structures are more complex data types, consisting of a number of data items of one or more data types. They include the record and array structures. An array consists of a number of elements of a single data type. An array may have one or more dimensions. A program refers to an element using the array’s identifier and an index number for each dimension. This approach enables efficient programs for filling an array, searching for a value in the array or generating output from its elements. Cambridge IGCSE Computer Studies
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2 1
Data
A shop has four students delivering newspapers to its customers. Each student delivers three different papers (RECORDER, MAIL and ARGUS). The shop manager uses a spreadsheet to record the deliveries as shown below: A
B
C
D
E
RECORDER
MAIL
ARGUS
PAID
1
NAME
2
LIZ
21
30
19
True
3
TOM
24
24
22
False
4
DAVE
19
16
26
True
5
PAM
18
12
23
False
6
TOTAL
Name the data type in cell: a A2 b D3 c E5. 2
The terms file, record and field are used in databases. Explain the meaning of each term and explain the connections between them; you may wish to include a diagram.
3
An estate agent uses a computer system to store details about properties for sale. A section of the properties file is shown below:
a b c 4
Property
Type
Area
Price
4217
D
Lake
99.92
4219
D
Park
200.00
4220
S
Lake
105.50
4221
F
Park
175.25
4222
F
Town
75.00
Why is coded data used for Type? What is the data type for Price? What is meant by a key field? Which is the key field?
a
What is meant by analogue data? b When does analogue data need to be changed into digital data? c What device performs the conversion? d Give one application which would use analogue data.
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5
a b
What is meant by digital data? Give one application which would use digital data.
6
Explain the following terms: a database b file c direct access file d record e sequential file.
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A shop sells bicycles. Information about each bicycle in stock is held in a computer file. Part of the information is shown in the table below. Make
a b c d e f g
Model
Type
Colour
StockNo
Price
Smith
Sprint
Racing
B
1471
$200.00
Thompson
Maxi
Racing
B
1329
$185.00
Brown
Speed
Racing
G
1654
$200.00
Davies
Swift
Mountain
R
1972
$0.15
Smith
Swallow
Racing
Y
2015
$300.00
Thompson
Fly
Mountain
B
2149
$400.50
Brown
Panther
Racing
Y
3249
$670.00
How many fields are shown? How many records are shown? Give a reason why the shop would need to delete a record from the bicycle stock file. Give a reason why the shop would need to add a record to the bicycle stock file. Explain how the shop can print a list of mountain bikes. There is an error in the table. Which item is wrong? How could this error have been avoided? Which is the key field?
8
A video club hires films to members. The club uses separate database files to store details about films, members and the films hired. a Name four suitable items of information for the FilmsHired database file, specify the field type and give an example of the data. b Name four suitable items of information for the Members database file, specify the field type and give an example of data.
9
a b c
What is meant by the term ‘validation’? What is meant by the term ‘verification’? Describe one method of verification when changing a password.
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2
Data
Below each answer there is a page reference for the coursebook. This is there to help you focus your revision. If you find that you get an answer wrong, you can use this guide to return to the coursebook to revise the areas that need some extra attention. Please note these are example answers only and do not represent the only possible answers. 1
The data type in cell: a A2 is text. b D3 is number (or integer). c E5 is Boolean (Yes/No). See ‘Data types’ on page 39.
2
A file is a collection of related data such as a set of data records. A record is a data structure that contains items of data about a thing in the real world. Each item of data within a record is known as a field.
fields ProdlD
Description
Price
Colour
A00345 A00346 A00348
widget, round widget, round widget, large hex
0.24 0.22 0.32
black metallic black
records
Products file See ‘File organisation and manipulation’ on page 37. 3
a
Coded data is used for Type because the full description would be longer. It would take up more storage space and may lead to errors in data entry.
b
The data type for Price is real or decimal (numerical data type).
See ‘Data collection’ on page 31. See ‘Data types’ on page 39. c
A key field is an item of data that uniquely identifies a record. In this case, the key field is Property. See ‘File organisation and manipulation’ on page 37.
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4
a b c d
Analogue data is data that changes continuously rather than in discrete jumps, for example, temperature or volume. It can be captured by a sensor. Analogue data need to be changed into digital data for it to be manipulated by a computer. An analogue-to-digital converter performs the conversion. A greenhouse control application would collect analogue temperature data and a computer would decide when to switch on and off a heater. See ‘Analogue-to-digital converters and digital-to-analogue converters’ on page 31.
5
a b
Digital data is data that changes in discrete, or stepwise, jumps. For example, the number of bikes sold or a person’s age. A utility billing application would use digital data from meter readings. See ‘Analogue-to-digital converters and digital-to-analogue converters’ on page 31.
6
a b c d e
A database is a set of tables that hold information about related things. (See page 8 or glossary.) A file is a set of data or program items held in a named area of storage (or a physical data structure). A direct access file is a file stored on disk. Its records can be accessed directly by using an algorithm to generate a record’s disk address from the record’s key value. A record is a set of data items about one type of thing. A sequential file is a file in which records are stored in order of their record key values. See ‘File organisation and manipulation’ on page 37.
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a
There are six fields (columns) shown. (See page 9 or glossary for definition of a ‘field’.) See ‘File organisation and manipulation’ on page 37.
b
There are seven records (rows) shown. See ‘File organisation and manipulation’ on page 37.
c
The shop would need to delete a record when a bicycle is sold.
d
The shop would need to add a record when a new bicycle is delivered from the supplier.
e
The shop can print a list of mountain bikes by selecting all records where the Type = ‘Mountain’. The price of stock number 1972 is incorrect. It could have been avoided by setting a limit or range.
See ‘File maintenance’ on page 39. See ‘File maintenance’ on page 39. f
See ‘Data validation’ on page 33. g
The key field is StockNo. See ‘File organisation and manipulation’ on page 37.
8
A video club hires films to members. a Four suitable items of information for the FilmsHired file are: Data item
Field type
Example
FilmID
Text or string, as no arithmetic will be performed
2759
Title
Text or string
Toy Story 3
Rating
Text or string
U
Price
Currency
2.50
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b
Four suitable items of information for the Members file are: Data item
Field type
Example
MemberID
Text or string, as no arithmetic will be performed
0648
Name
Text or string
John Smith
DateOfBirth
Date/Time
20/04/1996
PhoneNumber
Text or string
01536 739026 See ‘Data types’ on page 39.
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a
b c
The term 'validation' means examining input data to ensure that it falls within pre-set criteria. For example, a date of birth must be before a certain date to be valid for a pupil to be enrolled. The term 'verification' means double-checking that copied data is correct. One method of verification when changing a password is to ask the user to type it a second time, i.e. double entry. See ‘Data capture and checking’ on page 32.
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3
Hardware
Main hardware components of a general-purpose computer A computer is a programmable, electronic device. It receives input, stores and processes data, and produces output. Hardware means the physical parts of the computer. The main hardware components of a computer are: • input devices internal memory • a processor, which manipulates the data that the input device gives it • main memory (also known as internal memory), which holds data and processor output device input device programs while the computer is on • a backing storage device, which stores data and programs while the backing storage device computer is off • output devices.
Computers and processing power Computers vary in power. In descending order of processor power, they are: • supercomputer • mainframe • PC or laptop • netbook, palmtop or PDA. A computer is often embedded into an appliance in the form of a microcontroller, which combines the processor with memory, backing storage and other circuitry in a single integrated circuit.
Input devices You need to be able to select devices that are suitable for a particular computer application. Therefore, you must know what the different types of devices are, how they work and what they are used for: • keyboards and keypads • pointing devices (e.g. mouse, joystick) • image input devices (e.g. scanners, cameras and webcams) • input devices for sound and music (e.g. microphones, MIDI keyboards and other MIDI instruments) • remote controls (used to operate a TV, satellite or cable TV receiver, DVD player, home entertainment system or PC) • devices and methods for automatic data capture: – optical character recognition (OCR) software – optical mark reading (OMR) software – magnetic ink character recognition (MICR)
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– – – – –
•
barcode reader radio-frequency identification (RFID) reader magnetic stripe reader smart card reader biometric data capture device. Common types of device: – fingerprint reader – retina or iris scanner – microphone – camera – video camera sensors; common sensors include: – microswitch – reed switch – temperature sensor – pressure sensor – light sensor – infrared (IR) sensor – distance sensor – speed sensor – humidity sensor – moisture sensor – gas sensor.
Most sensors produce analogue signals that need to be digitised or converted into digital data by an analogue-to-digital converter (ADC).
Output devices As with input devices, you need to be able to select devices that are suitable for a particular computer application. Therefore, you must know what the different types of devices are, how they work and what they are used for: • monitor, e.g. a CRT or LCD screen • multimedia projector • printer or plotter, e.g. laser, inkjet and dot matrix • loudspeakers and headphones • actuators make physical changes; they include: – light bulb or LED – heater – heat-pump – solenoid – relay or contactor – motor – pump – buzzer and similar actuators such as bell, beeper or siren. Many output devices require analogue signals, so the computer’s digital output needs to be converted by a digital-to-analogue converter (DAC).
Specialised input and output devices Automated systems often use sensors and actuators together to do useful tasks, such as controlling a washing machine.
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Some computer applications require highly specialised input and output devices. An example is virtual reality (VR), in which the input devices include a wired glove, or data glove, and a VR suit containing sensors to detect changes of position. The main output devices are virtual reality headsets or virtual reality goggles, vibration actuators for wired gloves or VR suits to provide haptic (tactile) feedback for the user, and CAVE rooms in which panoramic images are projected onto the walls.
Internal memory and storage devices and their uses A computer holds programs and data in two sorts of device: • internal memory — limited-capacity and rapid-access during processing • backing storage — larger-capacity and slower-access to keep data/programs for future use. Internal memory
Internal memory consists of: • volatile, read-write, random access memory (RAM) to hold the programs and data currently being processed • non-volatile, read-only memory (ROM) to hold a small program to start a large operating system, the whole of a simple operating system or control program for an automated system or unchanging (lookup) data. Measuring the size of memory
Internal memory capacity is measured in power-of-two multiples of bytes. The correct binary prefixes are kibi-, mebi-, gibi- and tebi-, which are slightly larger than the corresponding widely used denary prefixes kilo-, mega-, giga- and tera-. However, the use of the denary prefixes is completely appropriate for hard disks. Backing storage
Backing storage has to be non-volatile and includes: • magnetic media, such as hard disks and magnetic tape • optical media, such as CDs, DVDs and Blu-ray discs • solid-state storage devices, such as flash-based memory sticks • digital storage cards. Different storage media have different characteristics that make them suitable for particular applications: • magnetic storage media – internal hard disk drive (HDD) is very cheap per gigabyte of storage and provides very high storage capacity with rapid direct access, which makes it suitable for a computer’s main backing storage – lightweight, pocket-sized, external hard disk drive is more expensive, but both removable and highly portable for safekeeping – magnetic tape drive is very expensive, but a magnetic tape cartridge is a cheap, high capacity, removable and highly portable storage medium, although access is very slow. This makes it more suitable for making backup or archive copies of the contents of an HDD • optical storage media – optical discs such as CDs and DVDs have smaller capacities than HDDs or tapes and are also more expensive per gigabyte of storage. They are also direct access media, with rather
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•
slower access than a HDD, and are removable and highly portable. The main types of CD and DVD have different suffixes, as follows: – ROM stands for ‘Read-Only Memory’ – these cannot be written to, and are suitable for the distribution of music, movies, software and encyclopaedias – R stands for ‘Recordable’ – these can be written to just once and then can only be read from, making them suitable for storing music or movies or archive copies of documents – RW stands for ‘ReWritable’ – these can be written to and read multiple times, making them suitable for making temporary copies of data files for transfer from one computer to another or regular backup copies – Blu-ray discs (BD or BR) have larger storage capacities than other optical storage media and a higher rate of data transfer. Although disks are expensive, their cost per gigabyte of storage is nearer to that of a HDD solid-state storage media – are electronic and made as integrated circuits or chips, currently using FLASH technology which, like ROM, holds data that are non-volatile, but can be erased and rewritten in large blocks – also known as non-volatile memory – devices often have multi-gibibyte capacities, are very small and portable, and are usually more robust than HDD or optical media. They include: – USB flash drives (memory sticks or pen drives) – flash memory chips – digital storage cards (DSCs) – solid-state drives (SSDs).
Mobile phones Mobile phones are examples of very widely used embedded computer systems. Some phones have a wide range of: • input • processing (including audio and video recording and playback) • storage • output • communication facilities. More people own mobile phones than computers, so in some parts of the world, people are more likely to access the Internet using a mobile phone than a computer. Smartphones have more flexible operating systems that can run more advanced application programs.
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3 1
Hardware
The diagram shows a personal computer system. Name the components and classify them as input, output, storage, communications or processor. D
C
E
A B
2
Name the data input type and the associated reader used to input the following characters and patterns into a computer. a b
c
3
centre
group
student
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
3
3
3
3
3
4
4
4
4
4
5
5
5
5
5
Indicate whether each of the following devices is an input device or an output device: a mouse b monitor c plotter d speaker e keyboard f scanner.
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4
Give an example of the use of each of the following: a barcode reader b magnetic ink character recognition (MICR) reader c optical mark reader (OMR).
5
Give two ways in which words can be input to a computer without using a keyboard.
6
Name three pointing devices and the type of computer system on which they are most often used.
7
Describe the input devices used at an ATM machine.
8
Name three different types of sensor used to input data in a control application.
9
Define the term backing storage and explain why computers need backing storage.
10
a b c
Name a storage device used by large organisations with large volumes of data where speed of access is not important. Describe two applications where it could be used. What kind of data access does it provide?
11
Describe the advantages and disadvantages of the different forms of optical storage media.
12
What is meant by the term ‘backup’? Why is it needed?
13
ROM and RAM are two types of memory found in computers. a What do the letters ROM stand for? b What do the letters RAM stand for? c What is the main difference between RAM and ROM? d Complete the following statements with ‘RAM’, ‘ROM’, ‘backing storage’. i .......... stores a copy of your work when the computer is switched off. ii .......... stores application programs and data while the computer is running. iii .......... stores programs that must be available as soon as the computer is switched on.
14
Complete the following sentences by using the correct words from this list: eight, gigabytes, memory, RAM a A byte is a unit of computer …………… and it consists of ……………. bits. b A school computer may have two ………………….. of ………………….. .
15
Indicate which of the following statements are true or false: a ROM stands for Read-Only Memory. b Data can be saved in ROM. c The internal memory of a computer can store software and data. d Data that changes is normally held in ROM. e Data on magnetic tape has to be read serially. f An airline booking system would probably use hard disk drive as backing storage. g A CD-ROM is an optical disk.
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Revision questions: 3 Hardware
2
3
Hardware
Below each answer there is a page reference for the coursebook. This is there to help you focus your revision. If you find that you get an answer wrong, you can use this guide to return to the coursebook to revise the areas that need some extra attention. Please note these are example answers only and do not represent the only possible answers. 1
D. keyboard – input
C. computer – storage and processor
E. telephone – communications
A. monitor screen – output B. printer – output
See Chapter 3 as a whole. 2
a b c
This is an example of magnetic ink characters. They are read by a magnetic ink character recognition reader (MICR). This is an example of a barcode. It is read by a barcode reader. This is an example of a specialised form for data collection by optical mark recognition. It is read by an optical mark reader (OMR). See ‘Devices and methods for automatic data capture’ on page 60.
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a b c d e f
A mouse is an input device. A monitor is an output device. A plotter is an output device. A speaker is an output device. A keyboard is an input device. A scanner is an input device. See ‘Input devices and their uses’ on page 49 and ‘Output devices and their uses’ on page 71.
4
a b
c
A barcode reader is used at a supermarket checkout to find the price for an item by reading the data stored in the item’s barcode. A magnetic ink character recognition (MICR) reader is used in a bank to process cheques. The cheque number, bank sort code and account number are printed in magnetic ink so the MICR reader automatically enters them into the system. The operator has to enter the amount. An optical mark reader (OMR) is used to mark multiple-choice exam papers. See ‘Devices and methods for automatic data capture’ on page 60.
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Answers to Revision questions: 3 Hardware
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5
Words can be input to a computer using a microphone with voice recognition software and using a scanner with optical character recognition software (OCR). See ‘Sound and music capture devices’ on page 58 and ‘Devices and methods for automatic data capture’ on page 60.
6
A mouse is used on a desktop computer. A touchpad is used on a laptop. A touchscreen is used in a kiosk (e.g. a ticket machine in a train station or airport). See ‘Manual input devices’ on page 49.
7
An ATM machine uses a numeric keypad and buttons at the side of the screen. It may also use a touchscreen for some buttons. See ‘Manual input devices’ on page 49.
8
Temperature, pressure and humidity sensors can be used to input data in a control application. See ‘Sensors’ on page 66.
9
Backing storage is a long-term non-volatile storage that stores programs and data for future use. Computers need backing storage so that programs and data can be stored after the power has been switched off. See ‘Backing storage’ on page 81.
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a b c
Magnetic tapes could be used to store large amounts of data where speed of access is not important. Magnetic tapes can be used in batch-processing applications, such as payroll and utility billing. Magnetic tapes provide serial data access. See ‘Magnetic storage media’ on page 82.
11
A DVD drive uses a more precise laser and can fit more data on the disc than a CD, but DVD drives and media are more expensive than CD drives and media. Similarly, Blu-ray discs store more data and are more expensive than DVD media. Recordable media cost more to produce than ROM discs, but allow the user to archive large amounts of data. Re-writable media are even more expensive, but allow the user to record many times on the same disc. See ‘Optical storage media’ on page 84.
12
A ‘backup’ is a copy of data. It is needed to recover data if the working medium becomes corrupted or damaged. See page 84.
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a b c
d
ROM stands for ‘read-only memory’. RAM stands for ‘random access memory’. RAM is volatile storage and ROM is non-volatile storage. Data in RAM disappears when a computer is switched off – it holds programs and data that are being worked on. Data in ROM cannot be changed after manufacture – it holds the computer’s boot information. Complete the following statements with ‘RAM’, ‘ROM’ or ‘backing storage’: i Backing storage stores a copy of your work when the computer is switched off. ii RAM stores application programs and data while the computer is running. iii ROM stores programs that must be available as soon as the computer is switched on. See ‘Internal memory and storage devices and their uses’ on page 79.
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14
Complete the following sentences by using the correct words from this list: eight a b
gigabytes
memory
RAM
A byte is a unit of computer memory and it consists of eight bits. A school computer may have two gigabytes of RAM. See ‘Measuring the size of memory’ on page 80.
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Indicate which of the following statements are true or false: a ROM stands for Read-Only Memory – TRUE. b Data can be saved in ROM – FALSE. c The internal memory of a computer can store software and data – TRUE. d Data that changes is normally held in ROM – FALSE. e Data on magnetic tape has to be read serially – TRUE. f An airline booking system would probably use hard disk drive as backing storage – TRUE. g A CD-ROM is an optical disk – TRUE. See ‘Internal memory and storage devices and their uses’ on page 79.
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4
Systems and communications
Operating systems An operating system (OS) is system software that provides a uniform environment: • in which application programs can run • through which a user can run the application programs and perform housekeeping tasks. Functions of an OS
The main functions of a computer’s operating system are to: • complete its own loading into RAM when the computer is started up using a small firmware program stored in ROM or FLASH memory • manage user accounts and security • provide an interface for the user • control the application programs • manage the processor’s time • manage the allocation of internal memory • control peripheral devices keyboards, printers and hard disk drives • provide ‘spooling’ – temporary storage of input or output data for relatively slow peripherals • manage interrupt signals to the processor • perform housekeeping tasks, such as file indexing or defragmenting a HDD drive.
Types of operating system Types of operating system, which are not mutually exclusive, include: • a batch OS • a multi-tasking OS • a multi-access OS • a real-time OS of which there are two types: – a real-time transaction processing OS – a real-time process control OS • a network OS.
User interface A user interface, or human-computer interface (HCI), consists of all the hardware and software through which a user provides input to a computer or receives information from it. Types of user interface controlled by the OS include: • a command line interface • a graphical user interface (GUI), which often: – features Windows, Icons, Menus and Pointing devices (WIMP) – provides windows known as folders and sub-folders.
File management A file is a program or set of data saved in backing storage.
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Directories, sub-directories and folders
A file directory is an index of the contents of a storage drive or sub-directory (a subset of the drive’s contents). A GUI often represents a directory as a folder. Commands for file management
• • • •
listing, sorting and searching the contents of a storage drive or folder moving contents between drives or folders copying contents between drives or folders printing a file without having to open it in an application program window.
Peripheral device control Methods of communication between the OS and peripheral devices include the use of: • buffers • polling • interrupts • handshaking • a checksum.
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Systems and communications
1
What is an operating system? List four functions of an operating system.
2
Describe the features of: a a command line interface; b a graphical user interface.
3
Computers have become more user-friendly with the development of graphical user interfaces. a Give four features of a graphical user interface. b Give two possible future developments to user interfaces.
4
Draw a diagram to explain how folders are structured on a hard disk.
5
List four functions of a file manager.
6
Explain the meaning of these computer terms: a buffer b peripheral device c interrupt d polling e handshaking.
7
Describe, using an example, how the operating system communicates with peripheral devices and maintains data integrity.
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Revision questions: 4 Systems & communications
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4
Systems and communications
Below each answer there is a page reference for the coursebook. This is there to help you focus your revision. If you find that you get an answer wrong, you can use this guide to return to the coursebook to revise the areas that need some extra attention. Please note these are example answers only and do not represent the only possible answers. 1
An operating system is a set of programs and data files that manages a computer’s hardware and the other programs that run on the computer. It controls the peripheral devices, allocates memory between application programs, performs housekeeping tasks on the backing storage, shares the processor between application programs. See ‘Functions of an operating system’ on page 93.
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a
b
A command line interface requires the user to type commands at a keyboard. The user needs to remember the commands (although help is usually available) and the string of options can be complex to get right. Only one command (program) at a time can be executed. A graphical user interface enables the user to use a pointing device to select commands and options from menus. Several programs can be open in various windows. See ‘User interface’ on page 98.
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a b
A graphical user interface uses windows, icons, menus and a pointing device. In the future, user interfaces may use voice commands or gestures to control the computer. See ‘User interface’ on page 98.
4
Disk C:\
Folders
Files and sub-folders
Programs My Documents Letter 2011-Jan.doc Photos France 2010 John birthday Hampton Court Homework timetable.doc tudors.doc Recycle Bin
ICT survey.xls
See ‘File management’ on page 101.
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5
A file manager enables the user to print, copy, move and list files. See ‘File management’ on page 101.
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a b c d e
A buffer is an area of memory that holds data temporarily ready to be sent to a program or peripheral device. A peripheral device is a device that links to the processor, such as a printer, a monitor or a webcam. (See page 93 and glossary.) An interrupt is a signal from a peripheral device or a program to the processor asking for some service (e.g. a printer may send an interrupt to ask for more data). Polling is a process in which the processor asks each peripheral device in turn if it needs a service. Handshaking is a process in which a peripheral device and the processor (or two computers on a network) establish communication. See ‘Peripheral device control’ on page 102.
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The operating system handshakes with the peripheral device (e.g. a printer) to establish initial communication. The printer driver fills the print buffer and requests the host controller to send the data to the printer. When the printer has dealt with the data, it tells the driver to fill the buffer again. This means that data is not sent too quickly and does not get ‘lost’. See ‘Peripheral device control’ on page 104.
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5
Types of computer system
Batch processing systems A batch processing system uses a batch operating system to holds batch jobs in a queue and run batch programs to process batches of data, known as jobs. It has the following characteristics: • a large batch of data is processed in one go, without operator intervention, usually at an off-peak time • the output is not time-dependent • the processing performed by the batch program is usually straightforward and the same from one set of data to the next.
Interactive systems An interactive system uses an interactive operating system and user interface to run interactive programs that allow the user to interact directly with the running programs to influence the future course of processing. An interactive system may be single-user or have multiple simultaneous users.
Network systems A network system uses network operating systems to allow two or more computers to perform processing independently while sharing controlled access to facilities such as file storage, servers and printers. A network system requires: networked devices, such as workstation or server computers, or network-enabled peripheral devices such as printers • metal cable, fibre-optic cable, wireless or satellite connections • sufficient copies of an appropriate network operating system.
•
A network can be connected in different patterns or topologies. Three basic network topologies are: bus network – see Figure 5.3 in the coursebook ring network – see Figure 5.4 in the coursebook star network – see Figure 5.5 in the coursebook.
• • •
The scale of networks may be: local (LAN) or single-site, typically using network cables, fibre-optic cables or wireless links wide (WAN) or multiple-site, typically using telephone lines, fibre-optic cables or satellite links.
• •
The best-known WAN is the Internet. To distinguish them from public web services on the Internet, private web-based services on a LAN are known as an intranet. An externally accessible intranet is known as an extranet.
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Control systems A control system uses one or more control programs running on one or more computers. There are suitable sensors for measurement and feedback, actuators and user interface devices to regulate the operation of other devices, with some monitoring and recording of physical quantities. There is some analysis of performance and considerable user interaction. The system is described as ‘real-time’, as it must be able to respond within a specified time to changes in conditions.
Automated systems An automated system is an embedded control system. Typically it uses a microcontroller running a single control program, without a separate operating system, performing a single task with a fixed set of hardware including sensors and actuators. There is a simple user interface with limited scope for user interaction and usually limited ability to record and analyse data.
Multimedia applications and systems Multimedia include text, audio, still images, animation, video and interactivity (such as hyperlinks, hotspots, image maps, buttons and mouseovers). Multimedia applications include authoring programs for ‘movie files’ and Rich Internet Applications (RIAs), multimedia player browser plug-ins and presentation programs.
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5
Types of computer system
1
Describe a batch processing system, using the example of a specific application.
2
Define the following terms: a LAN b WAN.
3
Describe three network topologies, including a sketch.
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a b
5
a b c
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a b
What are the advantages of using a LAN? What are the advantages of using a WAN? What is the Internet? What hardware is needed to access the Internet? What software is needed to access the Internet? What is an intranet and why is it used? What is the difference between an intranet and the Internet?
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Revision questions: 5 Types of computer system
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5
Types of computer system
Below each answer there is a page reference for the coursebook. This is there to help you focus your revision. If you find that you get an answer wrong, you can use this guide to return to the coursebook to revise the areas that need some extra attention. Please note these are example answers only and do not represent the only possible answers. 1
In a batch processing system, data is processed all at once. A person does not need to interact with the computer as it is processing the data. For example, a utility-billing application is supplied with a customer database and a file of meter readings. It processes the meter readings to produce bills for the customers. See ‘Batch processing systems’ on page 107.
2
Define the following terms: a A LAN is a local area network. b A WAN is a wide area network. See ‘Types of network’ on page 111.
3
A bus network has computers connected in a line. All signals are sent to all computers. terminator computer
T-connector
printer
bus
A ring network has computers connected in a circle. The signals are sent in one direction until a computer accepts them. computers
printer server
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Answers to Revision questions: 5 Computer systems
1
A star network has computers separately connected to a central hub. A switch or server directs signals to the computer they are addressed to.
computer
hub, switch or server storage
printer
See ‘Network topologies’ on page 110. 4
a b
A LAN allows computers to share peripheral devices and WAN connections. Inside the LAN, computers are generally safe from malicious interference. A WAN gives users access to worldwide communications. Users can read data held on a computer anywhere on the WAN and can send messages to other people connected to the WAN. A WAN can connect several LANS. See ‘Types of network’ on page 111.
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a b
c
The Internet is a WAN. It connects networks and hosts sites on the World Wide Web. To access the Internet, a user needs a computer and some sort of modem linking the user to an Internet Service Provider (ISP). Usually it is a telephone landline modem, cable TV modem or mobile broadband modem. The user may also have firewall hardware to block unwanted network communication with their computer. To access the Internet, a user can use various types of software but a web browser is the most common. It can give access to web-based email but many users access email through a specific email client running on their computer. See ‘Types of network’ on page 111.
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a
b
An intranet is a private, web-based service on a LAN. A large organisation uses it to provide information to its employees through familiar web-based tools, such as web browsers. It is used because only employees can access it. An intranet is private and cannot be accessed by any member of the public, unlike the Internet which can be accessed by anyone through an ISP. See ‘Types of network’ on page 111.
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6
The system life cycle
Systems analysis The stages of the system life cycle are: • fact finding • feasibility study • analysis • design • implementation (building) • testing • documentation • implementation (changeover) • evaluation • maintenance.
Fact finding Fact-finding methods that the systems analyst uses to collect information about the current system are: • observation of current procedures • interviews • questionnaires • inspection of documents.
Feasibility study A feasibility study is a preliminary investigation of a problem and should have enough information to allow the analyst and the client to make a sensible decision to either carry on with the project or to abandon it. It includes: • a description of the existing system • the existing system’s problems and costs • success criteria for a new system • possible solutions including a proposed solution • a development plan • a cost/benefit analysis.
Analysis Analysis involves: • using fact-finding methods to collect further information • summarising this information using: – dataflow diagrams – system flowcharts • writing a requirements or objectives specification.
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Design This involves: • selection of software • drawing of output forms and reports • drawing of data collection and input forms • specification of: – any automatic data capture methods – validation and verification checks – data storage – processing – command buttons and menus for navigation and processing – hardware – test strategy and test plan, including: – the sorts of testing to be performed – use of real and test data chosen to include: – normal data – extreme data – abnormal (erroneous) data.
Building and testing One or more programmers use the designs to build and document the software. The appropriate hardware and software is installed. The solution is tested according to the test plan, with test results in the form of ‘before’ and ‘after’ screenshots and comments. In the case of printed output, the actual output should be included as the ‘after’ evidence. See, for example, Figure 6.11 in the coursebook.
Documentation Technical documentation
The purpose of this documentation is to provide technical personnel with: • a detailed explanation of how the system works • information to assist them in: – routine hardware, software or file maintenance tasks – corrective maintenance – adaptive maintenance – perfective maintenance – future development of a replacement system. Its contents include: • the purpose of the system • the limitations of the system (things it does not do) • hardware and software requirements • system flowchart • processing • file types and structures • validation and verification checks.
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User documentation
The purpose of this documentation, known as the user guide or manual, is to tell people who use the system: • what the system does • how to use the system • not how the system does what it does. Its contents include: • the purpose of the system • the limitations of the system (things it does not do) • hardware and software requirements • comprehensive instructions on how to use the system • sample runs • error messages • troubleshooting guide • frequently asked questions.
Implementation (changeover) This involves: • installing and commissioning new hardware, software and data files • training new or existing staff members how to use the new system • choosing the method of implementation from: – direct – phased – pilot – parallel running.
Evaluation After installing a new system, it is necessary to evaluate it to find out whether it is effective in fulfilling the client’s requirements. An evaluation of the new system is carried out by documenting: • a comparison of the facilities of the new system with the requirements and objectives specification • a comparison of the test results from the new system with the expected results and with results from the previous system • a comparison of the performance of the new system with the requirements and objectives specification • users’ responses to the new system • any expected or unexpected limitations in the facilities or performance of the system • a description and prioritisation of any necessary improvements.
Maintenance The technical documentation should support three forms of maintenance: • corrective • adaptive • perfective.
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6
The system life cycle
1
Name the stages of the system life cycle.
2
A sports club wants to use a database to store membership details. a What data should be collected? b What should you take into account when designing the screen layout for the data entry? c Design a screen layout for your chosen data.
3
A supermarket has decided to change from a manual order-processing system to a computerised one. a Describe three methods of fact finding that should be used. b Describe two ways in which the staff could be trained to use the new system.
4
Name the two types of documentation that should accompany the solution to a problem.
5
A small business has decided to change from a manual wages system to a computerised wages system for producing the employees’ pay. a State three tasks in the analysis of the existing system. b State three types of test data that should be used to test the program. c Name the three different types of system maintenance that might be required by the new system.
6
In the context of data entry where the value should be between 0 and 100 inclusive, give two examples of each type of test data.
7
Describe four methods of system implementation. For each method of implementation, identify a situation where it is most suitable.
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Revision questions: 6 The system life cycle
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6
The system life cycle
Below each answer there is a page reference for the coursebook. This is there to help you focus your revision. If you find that you get an answer wrong, you can use this guide to return to the coursebook to revise the areas that need some extra attention. Please note these are example answers only and do not represent the only possible answers. 1
The stages of the systems life cycle are: • fact finding • feasibility study • analysis • design • building and testing • documentation • implementation (changeover) • evaluation • maintenance. See ‘Overview’ on page 117.
2
A sports club wants to use a database to store membership details. a The sports club should collect data about the members: names, addresses, phone numbers, dates of birth (if relevant). b When designing a screen layout for data entry, you should take into account the logical order of asking for information and the layout of a paper form if there is one. c A possible screen layout would be: Title
First name
Surname
Date of birth (dd/mm/yyyy) Address Postal code
Phone number
See ‘Input screens’ on page 129. 3
A supermarket has decided to change from a manual order-processing system to a computerised one. a Fact finding methods that should be used are observation of current procedures, interviews and inspection of documents. Questionnaires could also be used in some instances. See ‘Fact finding’ on page 119. b
The staff may be trained to use the new system by classroom training or using computerbased training (CBT). In classroom training the staff are the students and a tutor is brought in to train them on the new system. This is useful because it allows questions to be asked and answered immediately. In CBT, each staff member gets a DVD with the training on it so they can learn at their own pace. See ‘Training’ on page 140.
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4
A solution should be accompanied by technical and user documentation. See ‘Documentation’ on page 136.
5
a
Three tasks in analysis are fact finding, creating a requirements specification and defining the flow of data through the system.
b
Programs should be tested with extreme and abnormal data, as well as normal data.
See ‘Analysis stage’ on page 122. See page 134. c
The new system might require corrective maintenance (fixing software errors or ‘bugs’), adaptive maintenance (to reflect changes in the organisation’s requirements) or perfective maintenance (ways to improve the performance of the system). See ‘Maintenance’ on page 144.
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a b
The three types of test data used in a testing strategy are normal, extreme and abnormal data. If a value should be between 0 and 100 inclusive, examples of test data are: • normal: 28 and 79 • extreme: 0 and 100 • abnormal: −1 and 110. See page 134.
7
Four methods of system implementation are direct, phased, pilot and parallel running. a Direct implementation is most suitable when a system is small and not critical to business running. b Phased implementation is most suitable when the system can be divided into distinct phases that do not directly impact on each other. c Pilot implementation is most suitable when a small part of the business, such as a branch, can be operated independently from other parts. d Parallel running is most suitable when data is critical to the business and it can be evaluated over a short time. See ‘Implementation (changeover) stage’ on page 140.
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7
Range and scope of computer applications
The relevant characteristics of an application of computer technology are: • its purpose • its hardware and software components • the collection, preparation and capture of its data • its data storage structure • the outcome required and format of output • user interface • method of backup and system recovery • effectiveness • effects on individuals and organisations.
Communication systems These include: • email • video-conferencing • digital telephones • internet telephony • broadband and dial-up connections to a WAN, usually the Internet through an Internet Service Provider (ISP) • wireless network technology • multimedia applications.
Information systems This very large range of applications involves retrieving information from a database and updating the information in some way. An information system needs its data protected from accidental loss, so backup and rapid recovery are important. Booking systems
These involve accessing a database of seats for entertainment or travel, searching to find available seats and purchasing tickets, either with or without seat reservations. Medical information systems
These include: • medicine information systems for doctors or patients to check safety and drug interaction information • hospital information systems: – electronic patient records (EPR) – hospital administration.
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Library systems
These are used in libraries in order to keep records of books and other resources that are available for loan, borrowers and loans of resources to members. Office automation
Many organisations have improved efficiency by using databases shared by all their departments as a common pool of data. Organisations also use workflow management systems to define a series of tasks to achieve an outcome. Centralised application software can manage the contents of a file in a database, and allow tens of workers or students with different levels of access to collaborate by simultaneously either editing or viewing the contents of the file in real-time. Virtual reality
A virtual reality (VR) system creates computer-generated stereoscopic 3-D visual imagery and stereo sound of a simulated, virtual environment. VR involves specialised input and output devices (discussed in Chapter 3) and a relatively powerful computer with a large amount of RAM and compression software. Input data for VR must be obtained from CAD or similar software, or by sampling images and sound from the real world.
Commercial and general data processing Automatic stock control and order processing
An automatic stock control system is a real-time transaction processing system that records sales and deliveries. It automatically reorders fresh stock when the level falls to a minimum level and provides management information. Personnel records
Employers have to store records about their employees for purposes such as identification, attendance, payment, performance and training. Payroll
Employers or their payroll contractors use personnel records to calculate employees’ pay. Banking systems
Banking application software is used to: • maintain bank accounts • process cheques. Ecommerce Electronic funds transfer
An electronic funds transfer (EFT) is a computerised movement of financial credit from one account to another. It is used for payroll payments and bill payments by online banking and for card payments in shops.
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Internet shopping
An online shop has to maintain a web-accessible database with an illustrated catalogue that customers can browse and search. A customer must be able to add a specified quantity of a chosen item to a list of ordered items known as their ‘basket’ or ‘cart’ and also amend and delete items from their order. On completion of an order, the customer supplies their contact details and information about their payment card for EFT to the shop. Automated teller machines
An automated teller machine (ATM) is a machine found outside banks or shops and sometimes in indoor locations that gives a customer access to a limited range of banking transactions. Debit and credit cards
These cards are used for EFT as described earlier. The difference between debit and credit cards is the source of funds. With a debit card, a cardholder can only make a cash withdrawal or payment for goods or services with funds already in their bank account or with an overdraft (or credit) arrangement previously agreed with their bank.
Industrial, technical and scientific uses Modelling
Computer modelling is a tool for developing scientific understanding of physical, biological and social processes. A computer model does not involve a physical model, but uses program code based on a mathematical model, a set of formulae, to represent a real-world process. Simulation
A computer simulation is the use of a computer model to try to predict the future course of a process under specified external conditions. In some cases, this is performed simply to attempt to predict or forecast some behaviour or event and in other cases, to attempt to engineer a solution to a problem. Virtual reality
Virtual reality is a more ‘immersive’ method of interacting with a computer simulation than simply looking at a screen. Applications of VR include training operators, drivers and pilots, testing user interfaces and exploring new designs in 3-D. Computer-aided design
Designers use computer-aided design (CAD) to design products ranging in scale from jewellery to airliners. It is used for designing even the simplest of products because it is quick to create a design and modify it. It can accurately re-use proven parts of the design for new products. Some CAD software can verify the performance of the design by running tests on a simulated virtual product and produce estimates of materials required for, and costs of, production. A CAD system often requires a relatively powerful PC and non-standard input and output devices, such as: • a light pen • trackball or graphics tablet • a 3-D mouse for zooming, panning and rotating graphical models • a high-specification graphics card • multiple, large, high-resolution screens • plotters to draw scale and full-size drawings.
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Monitoring and control systems Such systems, each consisting of one or more computers: • need a real-time OS and real-time application • acquire data at frequent intervals from suitable combinations of sensors and, where necessary, ADCs • use suitable software to process the input data and usually provides the user with information for monitoring physical or chemical quantities and warning signals if limits are exceeded • may also record the data, as in data-logging, for future analysis • may use input data as feedback from a system being controlled so that software can make decisions about the required outputs to actuators, which may need to be converted to analogue form by DACs • may allow the user to interact with the information displayed and possibly to override automatic control. Monitoring systems
These include: • monitoring system for the body functions of hospital patients • burglar alarm • weather monitoring system • environmental monitoring. Monitoring and control applications
These include: • monitoring and control systems for industrial plants • monitoring and control systems for traffic.
Automation and robotics Automated systems
Such systems are: • very similar to computerised control systems but usually restricted to a single task, providing only limited interactivity for the user and lacking facilities for monitoring and analysing data • unless designed for data-logging, or audio, photographic or video recording, also less likely to include facilities for saving data • often based on microcontrollers. Household appliances
These include: • washing machine automated system • automated cooker or oven • lighting control • heating, ventilating or air conditioning control • embedded web technology (EWT). Electronic equipment
• •
camera television set.
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Satellite navigation devices
A global navigation satellite system (GNSS) is a system of at least twenty-four satellites in various orbits at an altitude of approximately 20,000 kilometres. The satellites broadcast frequent messages that enable a small satellite navigation (satnav) device containing a radio receiver and an embedded computer to calculate its location to within a few metres. The Global Positioning System (GPS) is a US military GNSS available to all users. Industrial robots
A robot is a machine that can repeatedly carry out a task under the control of a computer and whose task can be changed by reprogramming its computer. Robots can perform a wide range of repetitive production tasks. Closed-circuit television
Closed-circuit television (CCTV) is the use of one or more video cameras to produce video signals that are not broadcast, but displayed on a monitor screen. The images may be recorded. The camera may be remotely controlled by an operator or by a computer that receives data from sensors signalling an event of interest in a particular area. The computer’s software could react by panning, tilting and zooming the CCTV camera onto the area protected by the sensor and starting to record the camera’s video stream.
Expert systems An expert system is designed to support problem-solving by using the knowledge and rules of inference gathered from one or more human experts. An expert system can often solve problems using incomplete data, where the user answers ‘don’t know’ to a question or is not completely sure about their response. The essential components of an expert system (see Figure 7.49 in the coursebook) are: • a knowledge base that stores facts • a rule base that stores rules for decision-making • an inference engine that processes the user’s problem using the contents of the knowledge and rule bases • a user interface that enables the user to communicate with the inference engine. An expert system is created by: • collecting information from one or more experts • inputting factual information to the knowledge base • inputting decision-making rules to the rule base • creating an inference engine that will process facts, rules and data about the problem to be solved from the user • creating a user interface for: – input that will ask the user questions about their problem – output that will deliver proposed solutions with explanations • testing the system with a variety of inputs for which certain outputs are expected • producing a user manual and training users of the system.
Education, training and entertainment Computer-based learning
Computer-based learning, also known as computer-assisted learning (CAL) or computer-based training (CBT), consists of the multimedia presentation of interactive learning activities.
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Virtual reality in training
VR simulation or, with haptic (tactile) feedback, augmented reality (AR) simulation can be extremely useful in training. They can provide a trainee with visual and haptic (tactile) instruction from a virtual tutor and completely safe practice in techniques that would otherwise be hazardous to the trainee or others. Applications in music
• • •
musical composition software performance: – pitch correction software recording.
Animation
Animation consists of displaying a rapid succession of 2-D or 3-D graphics or model arrangements to create the illusion of movement. It is used for web presentations and advertisements and for film and television.
Use of the Internet Websites
A website is a collection of web pages containing text, graphics, video and sound. A website is hosted on a web server on the Internet. The information in the website can be viewed by other Internet users using a web browser. Websites are used to raise the profile either of a person or an organisation and to communicate with others. Some applications of websites are: • online shopping • online banking • search engines. Internet Security
To prevent the interception of private information such as shopping account, card payment or banking account information and particularly passwords or confidential messages, encryption (secret encoding) is used when: • a web server and browser use the secure HTTPS protocol • email client software: – creates a ‘digital signature’ to be sent with an email – encrypts the text of the email to prevent anyone who intercepts it from reading it • an online banking customer uses a hand-held smart card reader and their PIN to generate a numerical one-time password (OTP). People’s fear of the Internet
People’s worries about the risks when using the Internet include: • encountering offensive websites while searching for goods or services • downloading viruses during a transaction • being deceived by a bogus website and paying for counterfeit or non-existent goods • interception of shopping account, card payment or banking account information making them vulnerable to unauthorised access to their accounts (‘hacking’) or fraudulent transactions
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• •
browser ‘cookie’ files identifying their computer to a web server, enabling a trader to ‘retarget’ them receiving unsolicited email after they have been required to supply a valid email address in order to register for an account.
Effects of the Internet on society
Positive effects of the Internet on society include: • improved convenience • time-saving • improved access to information and services for people in remote locations or with disabilities • reduced cost of goods and services • reduced transport-related environmental impact from travel. Negative effects of the Internet on society include: increased risk of unauthorised access to our personal data environmental impact of computer use and maintenance of the satellite, cable, wireless and server infrastructure • reduced availability of bricks-and-mortar shops, banks and colleges and associated loss of employment • increased risk of fraud or misleading information • reduced face-to-face social interaction • reduced exercise and increased health problems • increased vulnerability of personal data • global culture may undermine local cultures.
• •
Intranets
Most websites can be accessed by anyone connected to the Internet. An intranet is a set of web-based information services accessible only within an organisation’s LAN or private WAN. An extranet is an intranet made available off-site to members or business partners of an organisation.
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Range and scope of computer applications
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Most schools now have computer networks for their administrative staff. a Name two jobs that could use the network. b Name two software applications that could be used. (HINT: Chapter 1 might be useful for this.)
2
Microprocessors are sometimes used in hospitals to monitor a patient on a life-support machine. Give one advantage of using a microprocessor rather than a doctor or nurse.
3
The temperature and soil moisture of a greenhouse must be controlled and must remain within a certain range. The temperature must be kept between 5°C and 30°C and the soil must not get too dry. Describe in detail how a computer system could be used to monitor and control both temperature and soil moisture in the greenhouse. In your answer state what items of hardware or equipment might be needed.
4
A large town uses computerised traffic lights, controlled by a central computer. a Give two types of input used by the system. b Give two benefits of the system.
5
Robots are now used in many different situations. a Name two different sensors that can be fitted to robots. b Describe how each of these sensors could be used. c List three jobs done by robots. d Give three reasons for using robots instead of people.
6
The Internet is widely used within a school. When pupils log on, they get the choice of the following Internet facilities allowed by the school. instant messaging a b c
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search engines
favourites
social networks
Select two of the above facilities. Define each facility and describe how each could be used in school. Give two problems or dangers that might occur when pupils have unsupervised access to the Internet. Explain how they could be prevented. In order to protect pupils which of the above facilities should be withdrawn?
A spreadsheet could be used to produce a simulation model. a Give a definition of a simulation model and state one example of where a simulation model could be used. b Give an advantage of using a simulation model.
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A number of schools are considering using video conferencing. a What is meant by ‘video conferencing’? b The schools already have computers. Give two additional pieces of hardware needed to enable video conferencing. c Give two advantages to the schools of using video conferencing.
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a b
Name five microprocessor-controlled devices in an average home. Describe any social effects that these may have had.
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Range and scope of computer applications
Below each answer there is a page reference for the coursebook. This is there to help you focus your revision. If you find that you get an answer wrong, you can use this guide to return to the coursebook to revise the areas that need some extra attention. Please note these are example answers only and do not represent the only possible answers. 1
a
Teachers could use the network to complete a computerised register and the senior management staff could send emails to the other members of staff. See ‘Communication systems’ on page 150.
b
2
Software applications that could be used are email clients, such as Outlook (see page 12) and web browsers, such as Firefox (see page 14).
A microprocessor can monitor the patient 24 hours a day, 7 days a week without getting tired or misreading data. See ‘Monitoring hospital patients’ on page 179.
3
A thermometer could be hung in the greenhouse and a humidity sensor could be stuck in the soil. Both sensors could be connected to a computer to set up an input feedback system. The computer would run a program that would test the sensor readings at regular intervals. If a reading fell outside the limits set in the software, the computer would then activate an actuator. If the soil became too dry, an actuator could run a sprinkler system for a time. If the temperature was too low, the actuator would close a window or start a heater. See ‘Monitoring and control systems’ on page 179 ‘Sensors’ on pages 66, 67 and 70.
4
a
b
Inputs used by the traffic lights system include those from sensors that tell if a vehicle is approaching the lights (or junction) and input from sensors that count the number of vehicles passing the lights. A computerised traffic lights system can be responsive to changing traffic conditions (unlike a timed system). It can also enable the traffic department to test out changes to the sequences of the lights. See ‘Monitoring and control of traffic’ on page 184.
5
Robots are now used in many different situations. a A robot could use pressure sensors and light sensors. b A pressure sensor could be used to ensure that the robot is touching an item before it carries out another action. A light sensor could be used to enable the robot to navigate around a workplace. See ‘Industrial robots’ on page 192 and ‘Pressure sensors’ and ‘Light sensors’ on page 68. c d
Robots in factories can be used for welding, placing parts and moving objects around. Robots can work in places or doing jobs that would be dangerous for people. Robots can work all day and night without breaks. Robots can accurately repeat a task many times. See ‘Industrial robots’ on page 192.
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6
a
Instant messaging is a facility that enables users connected to the Internet to ‘chat’ in realtime. A school could use instant messaging to give pupils the opportunity to exchange messages with pupils in other schools around the world. See ‘Communication systems’ on page 150 and ‘Instant messaging’ on page 13.
A search engine is a web application that indexes web pages (in its databases) and enables a user to run queries against the index. School pupils could use a search engine to find information for a project. See ‘Search engines’ on page 206 and on page 15.
Favourites are a facility of a web browser that enables a user to save the address of a page so that it can be accessed quickly. A school could provide its pupils with a set of favourites that are for recommended websites. See ‘Web browsers’ on page 14.
A social network is a website that enables users to exchange messages, photographs and other personal information. A school could have a social networking site to share information about its students to other members of the student body. See ‘Social networking websites’ on page 232. b
If pupils have unsupervised access to the Internet, they may access inappropriate material or download malware. Access to inappropriate material can be reduced by using parental control software to block certain sites. Anti-virus software can reduce the risks from malware. See ‘Computer viruses’ on page 227.
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c
In order to protect pupils, it would be better for the school to withdraw access to instant messaging and social networks.
a
A computer simulation is a model of the data in a real-world situation. A small business could store its accounts on a spreadsheet and create a simulation of its future performance under different conditions. A computer simulation makes it easier and cheaper to try out alternative scenarios to arrive at the best solution to a problem.
b
See ‘Simulation’ on page 173. 8
a b c
Video-conferencing means using both video and audio feeds over a network to connect people in a virtual ‘meeting’. Hardware needed for video-conferencing includes webcams and microphones. Advantages of video-conferencing are that meetings can be held at short notice and people do not have to spend time travelling. See ‘Video conferencing’ on page 151.
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a b
A games console, a microwave oven, an MP3 player, a DVD recorder and a sound system are all controlled by a microprocessor. These devices may contribute to people living more separate lives – it is much easier for people in a family to eat at different times, to watch TV programmes separately (or the same programme at different times). See ‘Automation and robotics’ on page 185.
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Social and economic implications of the use of computers
Social and economic effects of applications of computers The economic advantage of computerisation is increased productivity compared with manual systems resulting from computers’ ability to: • communicate and process data repetitively, more accurately and rapidly than humans • store data much more compactly than in paper documents • make cheap backup copies of data rapidly and reliably • search for information extremely rapidly and reliably • produce output rapidly in a variety of formats. Often, computerisation enables or even requires changes to the working environment, business methods or processes and the services provided by an organisation. Computerisation has changed patterns of employment. It has a tendency to result in the de-skilling of some jobs. Some jobs can be carried out by teleworkers and others are liable to be moved offshore. Workers often have to re-skill to remain employable. Health and safety
Spending long periods using a computer can make workers susceptible to a range of preventable health risks.
Health risk
Prevention
Reduced physical exercise and circulation in the legs.
Regular alternative tasks or short rest breaks.
Poor posture can cause back, shoulder and neck problems.
Ensure that the chair supports the worker’s back and the keyboard and screen are at the right height.
Sore eyes. Lack of exercise for focusing muscles of the eye over their full range.
Blink and look away from the screen regularly. Have regular eye tests. Avoid bright reflections from the surface of the screen.
Repetitive strain injury (RSI).
Use a padded wrist rest to support the hands and regularly stretch wrist and arm muscles in different ways.
Training methods A worker who works with a computer system needs to be trained properly when using a new system or an upgraded version of a familiar system. The worker may need training not only in how to use the new system’s hardware and software but also in the business processes to be used with
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it. CBT is a flexible way to re-train to meet changes in employment, although it does not provide immediate opportunities to ask questions.
Privacy and integrity of data Maintaining privacy of data involves preventing unauthorised access and accidental or malicious disclosure. Integrity of data means their completeness and correctness at all stages. Maintaining integrity involves: • avoiding corruption (unwanted changes to data) • making backup copies from which fresh working copies can be restored. It is important to maintain physical security measures around a computer system, such as: • not leaving it unattended at any time • locking the room in which it is kept, perhaps with a keycard system • monitoring the room with CCTV as a deterrent • locking the computer to a security cable • equipping the computer with a key-operated power switch. A LAN or single computer connected to the Internet needs firewall software to block unwanted communication from the Internet.
Security and reliability of data Data security can be defined as maintaining the privacy and integrity of data, together with protecting data against complete loss. A computer application’s requirements for security and reliability may include: • assigning different access rights or permissions • making backup copies • providing high availability by the use of redundant storage devices or computers.
Data protection legislation A data protection act is typically based on principles such as: • obtaining and processing personal data only fairly, lawfully and for specified purposes • keeping personal data accurate, up-to-date, sufficient, relevant and not excessive • deleting personal data when no longer needed • giving individuals right of access to the data held about them and to have factually incorrect information corrected • protecting data from corruption, loss and access by, or disclosure to, people who are not authorised to see them • not transferring personal data to another country unless that country provides a similar level of legal protection.
Hacking and other computer crime Threats to security and measures to combat them include: • the crime of gaining unauthorised access to computer data, known as hacking • other forms of computer crime including: – data theft – identity (ID) data theft, including phishing and pharming
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– – – – – – – – – •
fraudulent trading banking fraud espionage infringement of the copyright of software or music distributing or acquiring child pornography harassment (cyberstalking) child grooming distribution of malware denial-of-service attacks malware (which can be detected and removed by anti-virus software) including: – virus – worm – Trojan horse – scareware – spyware – crimeware.
Internet security Security problems posed by the Internet
Internet use poses security challenges from spyware, as well as hacking and malware. Spyware is malware that secretly collects various types of personal information from a user’s computer. Users are also vulnerable to Internet-based deception (or computer-based ‘social engineering’) such as: • phishing • pharming • advance fee fraud. Some other Internet security problems include: • spam • browser cookie files • adware.
Recent developments in the use of the Internet These include: • Web 2.0 sites, which allow account-holding users to contribute to the site’s content via a form viewed in a web browser: – social networking websites – web forums or message boards – wikis – digital media sharing websites • tagging • blogs and microblogs • feed readers • narrators • podcasts • peer-to-peer (P2P) file sharing protocols • mashups.
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8 1
a b
2
a b
3
a b
Social and economic implications of the use of computers What is meant by ‘software copyright’? Name three activities which would break software copyright. Define the term ‘hacking’. How can it be prevented? Define the term ‘computer virus’. How can a computer be protected against a virus?
4
Why is it important to secure data on a computer system?
5
What can be done to prevent the theft of data?
6
What is meant by the term ‘de-skilling’?
7
What effect has the use of computers had on patterns of employment? Identify areas where this has had a positive effect as well as those areas where it has had a negative effect.
8
a b c d
9
What is meant by ‘teleworking’? What hardware and software is needed by a teleworker? Give two advantages of teleworking for the employer. Give two advantages of teleworking for the employee.
List three principles on which data protection legislation is based.
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Social and economic implications of the use of computers
Below each answer there is a page reference for the coursebook. This is there to help you focus your revision. If you find that you get an answer wrong, you can use this guide to return to the coursebook to revise the areas that need some extra attention. Please note these are example answers only and do not represent the only possible answers. 1
a b
2
a b
Software copyright is similar to copyright in a book – it guarantees that the author or developer of the work is the person legally entitled to get commercial benefit from it. Copying a program onto a CD, putting it onto a web server and emailing it to someone are all activities that break software copyright. Hacking means gaining unauthorised access to a computer, locally or over a network. Hacking can be prevented by checking user credentials – requiring a valid username and password to gain access to the computer. See ‘Hacking’ on page 225.
3
a b
A computer virus is a piece of program code within a data or program file that copies itself and ‘infects’ other files in the same or another host computer. The effect of a computer virus can be prevented by running up-to-date anti-virus software. See ‘Computer viruses’ on page 227.
4
It is important to secure data on a computer system to reduce the risk of corruption and/or loss and to make sure it is only accessed by authorised users. See ‘Security and reliability of data’ on page 223.
5
The theft of data can be prevented by requiring a valid user name and password to gain access to a computer. See ‘Security and reliability of data’ on page 223 and ‘Computer crime’ on page 225.
6
De-skilling is the loss of skills due to using a computerised process to replace a worker with specific training and skills. See ‘Case study: Computerisation in a steel works’ on page 217.
7
The use of computers has decreased the number of skilled workers, such as those with practical skills in determining when materials are ready to move to another part of a manufacturing process, leading to de-skilling. However, computer use has also created new jobs in the fields of programming and computer maintenance. See ‘Case study: Computerisation in a steel works’ on page 217.
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8
a b
c d
Teleworking is a method of working in which an employee works from home or a remote office using telecommunication links. They may also connect to the employer’s network. A teleworker needs a computer, a telephone, a broadband connection (i.e. access to the internet) and networking software. Some might also need the tools required for video conferencing. Advantages of teleworking are that an employer does not need to supply buildings and furniture for all its staff. Advantages of teleworking are that an employee does not spend time and money travelling to work and that work can often be fitted around other commitments. See ‘Case study: Computerisation in a steel works’ on page 217.
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The principles on which data protection legislation is based are: • Personal data may only be obtained and processed fairly, lawfully and for specified purposes. • Data must be accurate, kept up-to-date, sufficient, relevant, not excessive and deleted when no longer needed. • Individuals have a right of access to the data held about them and to have factually incorrect information corrected. • Data must be protected from corruption, loss and access by or disclosure to people who are not authorised to see them. • Data must not be transferred to another country unless that country provides a similar level of legal protection for personal data. See ‘Data protection legislation’ on page 224.
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9
Algorithm planning and design
Creating a plan The main stages of planning any solution are: • understanding the problem • defining the scope of a solution – the extent of the facilities that the solution will provide • creating the solution • documenting the solution • testing the solution.
Creating the solution This involves: • top-down design or stepwise refinement • algorithms, which can be represented as – program flowcharts – pseudocode (see Chapter 10) • modules of code • menus.
Document the solution Techniques for documenting an algorithm include: • structure diagrams (see, for example, Figure 9.4 in coursebook) • program flowcharts (for symbols, see Table 9.1 in coursebook). For documenting the hardware required in a solution while showing much less processing detail, we can use system flowcharts, which have a much larger set of symbols (see Table 6.2 in coursebook).
Testing and interpreting algorithms Dry running is the process of thinking through the operation of an algorithm, to test it during design, for troubleshooting and to work out its purpose, if not stated. A trace table is a tabular record of a dry run. It has a column for each variable, usually in the order in which their values are first assigned. Each row is completed with the values of the variables whenever they change, moving to the next row when necessary.
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Algorithm planning and design
1
A school wants to calculate the number of hours spent in school by a sample of students from time of arrival and departure data. Draw a structure diagram and a program flowchart for an algorithm with the following features: a For each student, enter the student’s name, the time of arrival and the time of departure. b Calculate the length of time each student spends in school. c Output the student’s name and the time spent in school.
2
Consider the following algorithm. START
set Count, LowCount, HighCount to 0
Count = 10?
yes
output LowCount, HighCount
no STOP
input Temperature
Temperature < 18?
no
yes LowCount ← LowCount + 1
Temperature >= 30?
no
yes HighCount ← HighCount + 1
Count ← Count + 1
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a
Complete the following trace table using the temperature values 14, 17, 23, 27, 29, 30, 32, 26, 18, 12. Temperature
LowCount
HighCount
Count
0
0
0
Output
14
b 3
What is the purpose of the algorithm?
What is the purpose of the following algorithm? START
Count ← 0 Total ← 0
input Number
Number <0?
yes
no Total ← Total + Number
output Count, Total, Total / Count
Count ← Count + 1
STOP
input Number
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4
Read this algorithm. START
input a, b
a>b?
yes
no t ← b*2
t ← a*2
output a, b, t
STOP
a b
Write down the output if the two numbers input are 4 and 3. (a = 4 and b = 3.) Explain why an algorithm is written as a subroutine (procedure) and stored in a program library.
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9
Algorithm planning and design
Below each answer there is a page reference for the coursebook. This is there to help you focus your revision. If you find that you get an answer wrong, you can use this guide to return to the coursebook to revise the areas that need some extra attention. Please note these are example answers only and do not represent the only possible answers. 1
Structure diagram: calculate students’ times spent in school
process student data * while there are still any to process
input name, arrive time, depart time
calculate duration in school
print name and duration
Program flowchart: START
more data?
no
STOP
yes read name, arrive time, depart time
duration = depart time – arrive time
print name, duration
See ‘Structure diagrams’ on page 243 and ‘Program flowcharts’ on pages 244–5.
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2
a
Temperature
HighCount
Count
0
0
0
14
1
1
17
2
2
23
3
27
4
29
5
30
1
6
32
2
7
26
8
18
9
12 b
LowCount
3
10
Output
3, 2
The algorithm inputs 10 temperature readings and counts separately those of at least 30 degrees and under 18 degrees. It then outputs the number of low readings and the number of high readings. See ‘Dry running’ on page 247.
3
The algorithm reads a series of numbers until the number is less than 0. As long as the number is more than 0, it adds the number to a total variable and adds 1 to a count variable. Once the loop ends, it calculates the average of the numbers (Total / Count) and then outputs the count, the total and the average. See ‘Dry running’ on page 247.
4
a b
The output is: 4, 3, 8. An algorithm written as a subroutine (procedure) and stored in a program library can be re-used by other programs. The program can call the subroutine from the library file by temporarily passing control to it. See ‘Modules of code’ on page 242.
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10
Programs and pseudocode algorithms
The concept of a program A program is a sequence of instructions or programming language statements written to make a computer perform certain tasks. Well-structured programs require a programming language to support the following program constructs: • sequence • selection • iteration • subroutine. A computer’s processor can only run a computer program in the form of a file of machine code, which is a sequence of binary codes representing instructions for the processor. The instruction set for a family of processors is the machine language in which machine code is written for that family of processors. When machine code runs, the processor repeatedly: • fetches an instruction from internal memory • decodes the instruction • executes the instruction.
Programming languages Computer programming languages can be divided into two types: • low-level – closer to machine language • high-level – closer to English. Low-level languages
Machine language is the lowest-level sort of language, because the long string of zeros and ones in a machine code program is so difficult for a programmer to read or write. Each complete machine language instruction consists of an opcode (operation code), which may be as short as a single byte, even for a 32- or 64-bit processor. Some opcodes require one or more operands, which are numerical values or memory addresses upon which they operate.
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An assembly language for each family of processor is an alternative to machine language. Assembly code is easier to read and write than machine code, as two or more meaningful letters act as a mnemonic (memory-aid) for each machine language opcode. Assembly code (source code) must be translated into machine code (object code). This can be done manually, but it is quicker and more reliable to use a translation program called an assembler. High-level languages
High-level programming languages look far more like English or mathematical notation than low-level languages. They are much easier to read, write, test, debug and maintain, are problemoriented rather than machine-oriented, and are portable between different families of processor. A high-level language program must be translated into machine code before it can be run by a processor. This needs translation software that is more complex than an assembler, since one high-level language statement is translated into one or more machine language instructions. A high-level language program can be translated in two very different ways: • by a compiler program • by an interpreter program.
Pseudocode Pseudocode uses keywords commonly found in high-level languages and mathematical notation. It describes an algorithm’s steps like program statements, without being bound by the strict rules of vocabulary and syntax of any particular language, together with ordinary English. Arithmetic
Use the arithmetic operators in Table 10.4 of the coursebook. Assignment
Assignment is the process of writing a value into a variable (a named memory location). For example, Count ← 1 can be read as ‘Count is assigned the value 1’, ‘Count is made equal to 1’ or ‘Count becomes 1’. Another way of indicating assignment is a pseudocode statement such as: set Swapped to False
If an algorithm needs to read the value of a variable before it assigns input data or a calculated value to the variable, the algorithm should assign an appropriate initial value to the variable, known as initialisation. Input
We indicate input by words such as INPUT, READ or ENTER, followed by the name of a variable to which we wish to assign the input value. Output
We indicate output by words such as OUTPUT, WRITE or PRINT, followed by a comma-separated list of expressions.
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Totalling
To keep a running total, we can use a variable such as Total or Sum to hold the running total and assignment statements such as: Total ← Total + Number add Number to Total
Counting
It is sometimes necessary to count how many times something happens. To count up or increment by 1, we can use statements such as: Count ← Count + 1 increment Count by 1
Structured statements for iteration (repetition or loops)
Many problems involve repeating one or more statements, so it is useful to have structured statements for controlling these iterations or repetitions. Exit conditions consist of logical expressions whose truth can be tested, such as Count = 10 or Score < 0. At a particular time, a logical expression is either True or False. • WHILE…DO…ENDWHILE (see, for example, Figure 10.2 in the coursebook) • REPEAT…UNTIL (see, for example, Figure 10.3 in the coursebook) • FOR…TO…NEXT (see, for example, Figure 10.5 in the coursebook). Structured statements for selection (conditional statements)
These statements are used to select alternative routes through an algorithm, using logical expressions as conditions for the decisions involved. As with iteration (repetition), selection’s logical expressions often involve comparisons, which can operate on text strings as well as numbers (see Table 10.5 in the coursebook). • IF…THEN…ELSE…ENDIF (see, for example, Figure 10.7 in the coursebook) • CASE…OF…OTHERWISE…ENDCASE (see, for example, Figure 10.8 in the coursebook).
Producing algorithms in pseudocode Writing an algorithm in pseudocode is no longer graphical like a program flowchart, but is one step closer to writing program code in a high-level language. Producing an algorithm for a solution in pseudocode typically includes: • initialising any variables for totalling and counting • using REPEAT…UNTIL for input validation • using an appropriate loop structure for repetitions of data entry and/or other processing • using conditional statements to select appropriate processing alternatives • IF…THEN…ELSE…ENDIF statements for adjusting the values of maximum and minimum variables cannot be nested.
Testing and interpreting pseudocode algorithms Dry running a pseudocode algorithm with a trace table and test data helps to understand its behaviour and purpose.
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Revision notes: 10 Programs and pseudocode algorithms
3
Example problem Line 1 Exponent ← 0 Line 2 REPEAT Line 3
Result ← 2 ^ Exponent
Line 4
PRINT "2^", Exponent, " = ", Result
Line 5
Exponent ← Exponent + 1
Line 6 UNTIL Result > 100 Figure 10.11 What does this pseudocode algorithm do?
Example trace table Table 10.7 Trace table for pseudocode in Figure 10.11.
Result
PRINT
Exponent
Notes
0
Initialise variable
1
2^0 = 1
1
1st iteration
2
2^1 = 2
2
2nd iteration
4
2^2 = 4
3
3rd iteration
8
2^3 = 8
4
4th iteration
16
2^4 = 16
5
5th iteration
32
2^5 = 32
6
6th iteration
64
2^6 = 64
7
7th iteration
128
2^7 = 128
8
8th iteration
Example interpretation
The purpose of the algorithm is to print a list of the powers of 2 starting at 20 until it reaches the first one over 100.
Finding and correcting errors in pseudocode algorithms It is important to be able to identify errors and suggest corrections in a pseudocode algorithm. Common errors in pseudocode algorithms include: • missing or faulty initialisation of variables • faulty initial and final values for the control variable (loop counter) in a FOR…TO…NEXT loop • incrementing the loop counter in a FOR…TO…NEXT loop, which interferes with the automatic counting • failing to increment an optional counter variable in the other sorts of loop • failing to complete a structured statement with the requisite ending keyword ENDWHILE, UNTIL, NEXT, ENDIF or ENDCASE • misplacing a keyword, so that statements are inappropriately inside or outside a loop.
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Revision notes: 10 Programs and pseudocode algorithms
4
10
Programs and pseudocude algorithms
1
Write an algorithm to calculate the average of ten numbers. (Average = Total of the ten numbers divided by 10.)
2
What is the difference between machine code and a program written in a high-level language?
3
Write an algorithm which will input a sequence of eight numbers between 1 and 1,000,000, and print a list of all eight numbers together with the largest and smallest number in the list.
4
List four high-level programming languages.
5
Read this algorithm. Set Result to 0 INPUT Number WHILE Number >= 0 DO IF Number > Result THEN Result ← Number INPUT Number ENDWHILE OUTPUT Result
a b c
What is the purpose of this algorithm? What value of input will stop the loop and output the answer? Copy and complete the following trace table for the input values 6, 12, 8 and −3. Result
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Number
OUTPUT
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Revision questions: 10 Programs & pseudocude algorithms
1
10
Programs and pseudocode algorithms
Below each answer there is a page reference for the coursebook. This is there to help you focus your revision. If you find that you get an answer wrong, you can use this guide to return to the coursebook to revise the areas that need some extra attention. Please note these are example answers only and do not represent the only possible answers. 1
Sum ← 0 FOR Count ← 1 TO 10 INPUT Number Sum ← Sum + Number NEXT OUTPUT "Average = ", Sum / 10
See ‘Pseudocode’ on page 260. 2
Machine code is a program written in machine language that can be understood by a specific processor family. A program in a high-level language can be run on a number of different processors but must be converted to machine code by a compiler or executed by an interpreter. See ‘The concept of a program’ on page 255.
3
Largest ← -1 Smallest ← 1000001 FOR Count ← 1 TO 8 INPUT Number IF Number > Largest THEN Largest ← Number IF Number < Smallest THEN Smallest ← Number PRINT Number NEXT PRINT "Largest number is ", Largest PRINT "Smallest number is ", Smallest
See ‘Pseudocode’ on page 260. 4
COBOL, Delphi, C++ and Java are high-level programming languages. See ‘High-level languages’ on page 257.
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Answers to Revision questions: 10 Programs & pseudocode algorithms
1
5
a b c
The algorithm inputs a sequence of numbers and keeps a record of the largest number read so far. Once the loop ends, it outputs the largest number input. Any value less than 0 stops the loop and outputs the answer. Result
Number
0
6
6
12
12
8 −3
OUTPUT
12 See ‘Testing and interpreting pseudocode algorithms’ on page 266.
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Answers to Revision questions: 10 Programs & pseudocode algorithms
2
11
Logic gates and circuits
Logic gates A logic gate is an electronic circuit that processes two-state signals according to a logical rule. Each gate has one or more inputs and a single output. Unless otherwise stated, we associate the value True with 1 and On, and the value False with 0 and Off. We only need to consider the simplest five types of logic gates, AND, OR, NOT, NAND and NOR, with a maximum of two inputs. Table 11.2 shows symbols for the gates and defines their behaviours.
Truth tables A truth table is used to show the output of a logic gate or circuit for all possible combinations of input values; we usually use the binary values, 1 and 0, as shorthand for True and False. The truth table for a two-input gate needs four rows. The truth tables that define the behaviours of the five types of logic gate are shown in Figures 11.2 to 11.6 and Tables 11.3 to 11.7 in the coursebook.
Combinational logic circuits with two inputs Two or more logic gates can be connected to produce a logic circuit with one or more outputs from two or more inputs. A logic circuit can process logical expressions and binary numbers. When producing a truth table for a logic circuit, as in Figure 11.8 and Table 11.8 in the coursebook: • it is helpful to add a column for each intermediate output as well as for the final output • as for a single logic gate with two inputs, a logic circuit with two inputs needs four rows.
Combinational logic circuits with three inputs We only need to be able to produce a truth table for a logic circuit with a maximum of three inputs and six gates. The truth table for a three-input logic circuit needs eight rows. See, for example, Figure 11.9 and Table 11.9 in the coursebook.
Designing simple logic circuits Sometimes, it is cheaper to design and hard-wire a logic circuit for a simple automated system that only requires a fixed pattern of output depending on the current values of the inputs, than to program a microcontroller or computer.
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We can use the words AND, OR, NOT, NAND and NAND as operators in a logical equation, such as L = (A AND B) OR NOT B. We use brackets to indicate that the logical operation within the brackets takes priority. We can design a logic circuit to solve a written statement of a logical problem. First, we rewrite the statement using brackets to clarify the binary value of each variable and the priority of the logical operations. Then we can write the logical equation. From the logical equation, if not an earlier stage in the rewriting process, it should be possible to draw the required logic circuit and a truth table to confirm that it has the required behaviour. See, for example, Figure 11.11 and Table 11.10 in the coursebook.
Testing logic circuits We have seen how to use a truth table to check whether a logic circuit has solved a given problem, rather as we use a trace table for dry running a flowchart or pseudocode algorithm. We can also check that a logic circuit solves the problem by building the circuit using logic simulation software or electronic circuitry, with appropriate attention to safety.
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Revision notes: 11 Logic gates & circuits
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11 1
Logic gates and circuits
Identify each of the following logic gates from its truth table. a
b
c
d
e
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INPUT 1
INPUT 2
OUTPUT
0
0
0
0
1
1
1
0
1
1
1
1
INPUT 1
INPUT 2
OUTPUT
0
0
0
0
1
0
1
0
0
1
1
1
INPUT 1
INPUT 2
OUTPUT
0
0
1
0
1
0
1
0
0
1
1
0
INPUT 1
INPUT 2
OUTPUT
0
0
1
0
1
1
1
0
1
1
1
0
INPUT
OUTPUT
0
1
1
0
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Revision questions: 11 Logic gates & circuits
1
2
Copy and complete the truth table for the following logic gates. a AND
INPUT 1
INPUT 2
0
0
0
1
1
0
1
1
OUTPUT
b NOR
INPUT 1
INPUT 2
0
0
0
1
1
0
1
1
OUTPUT
3
Draw the logic circuit required to fulfill the following statements: a Output C = (NOT(A AND B)) AND (A OR B) b Light (L) is on if Switch A is on OR (Switch B is on AND Input C is off).
4
Copy and complete the truth tables for the following logic circuits: a
A AND
NOR B
C
NOT
INPUT A
INPUT B
0
0
0
1
1
0
1
1
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OUTPUT C
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Revision questions: 11 Logic gates & circuits
2
b
A AND NOT C
OR NOT AND
B
c
INPUT A
INPUT B
0
0
0
1
1
0
1
1
OUTPUT C
A AND D
OR B AND C
NOT
INPUT A
INPUT B
INPUT C
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
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OUTPUT D
Revision questions: 11 Logic gates & circuits
3
11
Logic gates and circuits
Below each answer there is a page reference for the coursebook. This is there to help you focus your revision. If you find that you get an answer wrong, you can use this guide to return to the coursebook to revise the areas that need some extra attention. Please note these are example answers only and do not represent the only possible answers. 1
a b c d e
This truth table is for an OR gate. This truth table is for an AND gate. This truth table is for a NOR gate. This truth table is for a NAND gate. This truth table is for a NOT gate. See ‘Truth tables’ on page 276.
2
a
INPUT 1
INPUT 2
OUTPUT
0
0
0
0
1
0
1
0
0
1
1
1
See ‘Truth tables’ on page 276. b
INPUT 1
INPUT 2
OUTPUT
0
0
1
0
1
0
1
0
0
1
1
0 See ‘Combinatorial logic circuits with two inputs’ on page 277.
3
a
A NAND AND B
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C
OR
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Answers to Revision questions: 11 Logic gates & circuits
1
b
A
L
OR B AND C
NOT
See ‘Designing simple logic circuits’ on page 279. 4
a
INPUT A
INPUT B
A AND B
NOT B
OUTPUT C
0
0
0
1
0
0
1
0
0
1
1
0
0
1
0
1
1
1
0
0
See ‘Combinational logic circuits with two inputs’ on page 277. b
INPUT A
INPUT B
NOT A
NOT B
A AND (NOT B)
B AND (NOT A)
0
OUTPUT C
0
1
1
0
0
0
0
1
1
0
0
1
1
1
0
0
1
1
0
1
1
1
0
0
0
0
0
See ‘Combinational logic circuits with two inputs’ on page 277. c
INPUT A
INPUT B
INPUT C
A AND C
B AND (NOT C)
OUTPUT D
0
0
0
0
0
0
0
0
1
0
0
0
0
1
0
0
1
1
0
1
1
0
0
0
1
0
0
0
0
0
1
0
1
1
0
1
1
1
0
0
1
1
1
1
1
1
0
1
See ‘Combinational logic circuits with three inputs’ on page 278.
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Answers to Revision questions: 11 Logic gates & circuits
2
