Nature, Capabilities and Limitations
Categories of Software
3 general categories :-
Written to perform specific tasks
such as order entry, payroll, stock control or hospital
May be designed specifically for a company
(‘bespoke software’) and written especially for them
using a programming language or software such as a
database management system
Alternatively, the software may be purchased ‘off the
Performance monitoring software
General purpose software
Includes all common application packages such
– word processing
– desktop publishing
– computer-aided design (CAD)
– presentation graphics
combine features from all five of these
once very popular
– single product
– at a relatively low price
– data could be transferred between applications
However, have fewer and less sophisticated
features than are found in separately purchased
offer several products packaged together
cheaper than buying the packages separately
– e.g. Microsoft Office
includes Word, Excel, Access, PowerPoint,
Publisher, PhotoDraw, FrontPage etc.
– Other Examples include
Generic or Specific?
– e.g. word processing, spreadsheet and database.
– This simply implies that any of the dozens of spreadsheet
packages, for example, can be made to do many different
tasks, and is not designed specifically for one type of
– e.g. a payroll or stock control system, or a software package
to help fill in an income tax return.
– Designed to do one particular task
Bespoke or off-the-shelf? (1)
Advantages of buying an off-the-shelf package
– generally less expensive
– it may be possible to speak to other users of the package for
their evaluation before buying
– can be bought and installed straight away
– software is tried and tested and likely to contain fewer bugs
than newly written software
– usually well documented
– training may be available in common packages
Bespoke or off-the-shelf? (2)
Advantages in buying tailor-made software
– designed to do exactly what the user wants
– can be written to run on specified hardware
– can be integrated with existing software
– may not be a suitable package available
Application packages that are used to
perform operations that are an integral part
of day-to-day business operations.
A program or set of programs used to enter, edit, format,
store and print documents. A document may be anything
from a simple memo to a complete book.
Word processors have several important features:
– Spelling and grammar checker
Each word in a document can be checked against words held in the
– Automatic creation of index and table of contents
Any word in the text can be marked for inclusion in an index, which
can be updated at any time.
– Import files
Tables, photographs, graphics and even video and sound files can be
imported from other sources and inserted in a document.
Word processor (cont.)
– Mail Merge
A document and a list of names and addresses can be
merged to produce personalised letters.
– Creation of templates
with preset text styles, margins, formatting, letterheading,
– WYSIWYG capability
‘What You See Is What You Get’
Format cells, rows and columns
– specifying for example, the alignment of text, number of
decimal points, height and width of cell;
Copy cell contents to other locations
– with automatic adjustment of formulae;
Determine effect of changes of data
– this facility is termed ‘what-if’ calculation;
Insert, move or delete rows and columns
– such as SUM, AVERAGE, MAX, MIN in formulae;
Spreadsheet features (cont.)
Create a simple database
– and sort or query the data to produce report of, say, all
females earning over £20,000;
– to automate common procedures;
– spreadsheets with formats and formulae already entered, into
which new figures may be inserted;
Create ‘multi-dimensional’ spreadsheets
– using several sheets, copy data between sheets;
Create many different types of charts and graphs
Database and Electronic Mail
e.g. PowerPoint. Useful for putting together a
presentation which can be delivered using a
computer attached to a projection device.
– slides with text, graphics and pictures
– animation or sound effects
– ‘transition’ effects between slides
Tips for creating a presentation
Start with a title screen to introduce the
Use a consistent style for each slide
Don’t put more than 4 or 5 points on each
slide - people can’t take in too much
information at once
Be sure the font size is large enough
to be read from all parts of the room
A piece of software that allows users to
generate their own applications without
having to do much programming e.g.
Paradox database software.
A piece of software that allows a user with
little knowledge of programming to specify
the format and content of a printed report to
be composed using values from a database
or calculations performed by a computer.
Examples :- Crystal Reports, RPG ( Report
Program Generator) and report wizards in
Shows a web page for which you have either
entered the URL or clicked on a ‘hot’ link;
Browses back and forward;
‘Bookmarks’ pages for quick reference;
Keeps a ‘History’ list of pages visited;
Saves pages for viewing off-line;
Shows animation sequences in Java script;
Plays back sound, video clips and multimedia;
Downloads files to a local hard disk;
Submits on-line forms by e-mail;
Allows access to some personal e-mail.
Computers require two types of software
– Applications software
such as word processing, spreadsheet or graphics
– Operating systems software
to control and monitor the running of application
programs, and allow users to communicate with the
Windows 3.1 Unix
Windows 9x Linux
Windows ME MacOS
Functions of an operating system
Resource allocation and scheduling
Backing store management
Allowing a user to communicate with the
– check disks and memory for viruses and delete them if
Security and accounting software
– checks user IDs and passwords, counts and reports the
number of attempts made to log on under each user ID, the
amount of processor time used at each session, total login
time and so on;
File management utilities
– attempt to repair corrupted files, reorganise files on disk so
that free space is ‘defragmented’, ‘zip’ (compress) files so
that they occupy less space.
DOS (Disk Operating System)
tells the computer how to format, read and write
information on disk (either floppy or hard)
manages peripheral devices such as printer and
controls the execution of application software
how many files can be held in a disk directory
what is an acceptable file or directory name
the number of bytes that can be on a disk
the amount of memory usable by a program
The user has to type in commands in exactly the
correct syntax to perform any operation
Experienced users may be able to perform
using DOS than by
using WIMP GUI
DOS with WINDOWS system
Full operating system (no DOS)
Work in 32 bit
Removed 8 character filename limit
New User Interface
Plug and Play (Pray!)
Windows NT4 (& 2000) use same UI
UNIX / LINUX
– General purpose, Multi-User, Multi-tasking
– Used on machines from many manufacturers (unlike
– GNU – freeware licence
– Becoming increasingly popular
– Many applications being ported to LINUX
Both started as CLI, but now have X-Windows
Capabilities of Software
Object Linking & Embedding (OLE)
OLE allows information to be shared between different
– For example, a spreadsheet created in Excel can be
included in a Word document either by embedding it in
the document, or by creating a link from the document.
An embedded object has no connection with its
original source file.
A linked object ensures that the information
displayed in the document will always be displayed
– via the link – directly from the source file.
Object Linking & Embedding (OLE)
– original information remains in the source file
– destination file displays a representation of the linked
information but stores only the location of the original
– linked information is updated automatically if you change
the original data in the source file
– Use if file size is a consideration
– becomes part of destination file.
– because an embedded object has no links to the source
file, the object is not updated if you change the original
Portability of Data
Portability is the ability to run the same program on
different types of computer. It can also refer to the
ability to transfer a file from one computer to another.
For all sorts of reasons, it’s important to be able to
transfer data between applications and between
computers of the same or different types, perhaps using
different operating systems.
Files (binary, text or graphical) can be downloaded from
the Internet using ftp (File Transfer Protocol) – software
that can copy files between different types of computer
Examples of Portability
You’re writing a report in Word and want to be able
to insert an Excel spreadsheet in the report
You’re using a desktop publishing system and you
want to be able to import some graphics from a
You’re doing a research assignment and want to
download articles from the Internet on ‘Computers
You want to e-mail your friend on a Unix machine in
Hull from your PC in Southampton, and send her a
scanned photograph she requested
Problems with portability
A document created using one word processing package (e.g.
Word) commonly cannot be read by a another (e.g. Word
Perfect) running on the same computer
Formatting codes vary in different packages.
– For this reason, most word processing packages allow documents to
be stored in ‘Text only’ format.
A document created on one computer using a particular word
processor appears differently on the screen of another computer
running the same word processing package.
– Some word processors (e.g. Word Perfect) lay out a document based
on the printer that is being used.
Another possible problem is that fonts used with the original
application may not exist, or be installed, on the new computer.
Upgradability upgrades about every two
Software manufacturers commonly bring out
years. This causes some or all of the following problems:
– Documents or applications produced by the upgraded software are
not ‘downwardly compatible’ (or ‘backwards compatible’).
In other words, a document written in Version 6 can usually be read in
Version 7, but not vice versa.
Usually, the newer version allows the user to save the file as a ‘Version
6 file’ so that it can be read by the earlier version.
– The new version is likely to contain new features non-existent in
earlier versions so that data or formatting may be lost if it is
converted to the earlier version for another user.
– The upgraded software frequently needs more memory, more disk
space and a faster processor to work efficiently meaning that
hardware has to be upgraded.
On the other hand, of course, a new version often brings impressive
improvements in ease of use, functionality and speed.
Criteria for selecting a software
Compatibility with existing hardware. Will the software run on existing
Compatibility with existing software. Can files from other packages be
Quality of documentation
Ease of learning. How good is the on-line help? Are tutorials available?
Ease of use. Easy to use? Shortcuts for advanced users?
Technical support. Is this available, and at what cost?
Upgrade policy. Will future upgrades be available at a discount? Can files
created in older versions be used?
Speed. How long does it take to perform complex but frequent operations
such as database queries?
Cost. May involve cost of an individual package or a site licence
Before selecting a particular package you could:
– Read reviews of it in a computer magazine.
Magazines commonly compare similar software packages on
dozens of different criteria;
– Consult other users who have experience of the type of
software you are thinking of purchasing;
– Perform benchmark tests (performance tests) to see how
fast various packages perform a number of different
tasks. Computer magazines often publish the results of
Batch systems are relatively easy to test.
– More controlled environment, where data is entered as batch,
processed and then output.
– Expected results easily compared with actual results
– Problems can be fixed and tests run again.
More complex on-line systems with GUI interfaces are much
more difficult to test:
– No single, well-defined flow of events at user interface.
– It is often nearly impossible to restore a database to the condition it
was in before a bug was detected.
– Continuous development techniques mean that new versions appear
to quickly for the testing to keep pace.
– User find ways to use the the new software in ways which were not
anticipated by the designers.
– Performance tests are very difficult to set up for massive, on-line,
Primary & Secondary Storage
– Volatile storage, such as RAM, is primary storage
– All contents lost when machine switched off
– Good practice to make regular back-ups
– Non-volatile, more permanent storage for software and
– For example:
Magnetic Tape, Magnetic Disks, CD-ROM, microfilm
Method usually depends upon whether every record
needs to be processed.
– Every record has to be read. Typically used in a payroll
– Each record has its own address allowing direct access
Address can be calculated from a unique key
Or retrieved from a separate index
– Typical in Database Management Systems
Floppy Disks & Zip Disks
– 3.5” Floppy Disk
Thin plastic disk (mylar) covered in metal oxide in a hard plastic case.
HD (high-density) disk can store 1.44 Mb
– Zip Disk
Slightly larger than floppy but similar construction
Hold 100Mb or 250Mb of data
– Disk Storage
Diskette has two surfaces, each with (typically) 80 concentric circles
Tracks are divided into sectors when disk is formatted
– One or more platters in a sealed casing.
– Typically 5Gb to 30Gb as of Spring 2001.
Minis & mainframes
– May be fixed or removable
– Fixed are faster, more reliable, greater storage capacity
– Similar storage in concentric track, but on multiple platters,
giving rise to concept of cylinders.
– Cylinder is the set of tracks that multiple read/write heads
access in one position.
Hard Disk layout
Magnetic Tape is obviously a serial medium.
– Have to read through tape to find a required record
– Updates require creation of a new tape
Data cannot be changed in situ
Cheap and convenient for backup
– Cartridge tape for PCs can store up to 20Gb
Data record in frames across the tape
One frame represents one byte
Frames form tracks along the tape, typically 9
tracks – 8 data tracks and one parity track
– Stores up to 700Mb.
– Various data types
– Read-only. Read by reflecting a laser beam off the surface
and detecting the presence or absence of tiny pits which will
have been burned into the surface to represent binary digits
WORM – Write Once, Read Many
– Similar to CD-ROM, but usually gold in colour
– Intended use for firms to store their own data for rapid
– Favoured by ‘pirates’ to produce illicit copies of software
– Integrate optical and laser technology for read and write storage.
– A 5.5” disk can store up to 2.6 Gb.
– Still under development, but may replace magnetic disks when price
and speed permit.
– COM (computer output on microfilm) devices create the4” by 6”
hard-copy films that are microfiche
– Each sheet may contain upto 270 frames each containing a page of
information which can be viewed using a special viewer
Keyboard data entry
Most common method of input device
Suitable for most applications (although not
always the nest method)
– It is easy to make transcription errors – that is, copy
the data wrongly from the document
– It is time-consuming
– Data entry operators who enter data all day every
day are prone to repetitive strain injury (RSI)
Voice data entry
The user speaks the text into a microphone
Special software interprets the text exports it to a
word processing package
The accuracy of the voice recognition system is
improved by ‘training’ it to a particular user’s
voice - still not 100% accurate esp with
technical / legal words
Needs a powerful machine!
Scanners / OCR
Scanners can be used to read typed documents
OCR (Optical Character Recognition) software can then
be used to interpret the text and export it to a word
processor or data file for editing
Very powerful OCR software can also convert neat
Scanners are also used to input large volumes of data
on pre-printed forms such as credit card payments
where data is in a specific place
Key to Disk (1)
Large amounts of data is collected on forms
Many operators sit at terminals and key data
to a disk
Data stored on disk is later added to main
Supervisor can see all operators data entry
speeds and number of errors!
Key to Disk (2)
Used by banks for cheque processing
– It is hard to forge the characters
– The characters can be read even if the cheque is
crumpled, dirty or smudged
– The characters are readable by humans, unlike bar
Disadvantages - COST
Bar Codes (1)
The pattern of lines represents numbers
A barcode consists of
– Country (2 or 3)
– Manufacturers code (5)
– Represent product details (5)
– Check digit (1)
What benefits might a supermarket get from using
Other uses for Bar Codes
– bar coded containers of raw materials are stored in racks of
bins which are also bar coded.
– bar codes used to identify blood and other samples.
– used to record loans and track stock.
Banking, insurance and local government
– for document control and retrieval.
Factors affecting choice
– Volume of output
High volume require fast, heavy-duty printer
– Quality of print required
– Location of printer
– Are multiple copies required?
– Is colour required?
Types of Printer
– Impact Printer - Print head has 9 or 24 pins
– Pins strike paper through a ribbon.
– 24 pins give better print quality – dots closer
– NLQ (Near Letter Quality) obtained by printing each line
twice, which second pass slightly displaced so as to fill any
– Printers are often bi-directional
– Very versatile
– Colour possible via 4-colour ribbon – but quality not too good
– Can be very noisy
Types of Printer
– Very popular – often bundled with PC
– Cheap with very good resolution, particularly on
– Droplets of ink are fired at the paper
– Large areas of colour may get the page too wet
unless special paper is used
– Colour printing can be quite expensive
Types of Printer
– More accessible now as prices come down
– Similar process to photocopier with toner images
being fused onto the paper by heat and pressure
– Very high quality
– Virtually silent
– Colour option can be very expensive
Used for high quality line drawings
– Building plans
– Circuit diagrams
Pen (Vector plotters)
– Draw images using point-to-point data, moving pen over the
– Low in price
Penless (Raster plotters)
– Electrostatic, thermal or laser plotters
Required for high-density images
Assemble drawings for machines
Three attributes: size, colour and resolution.
It has its own RAM to store the image on screen
Amount of RAM will determine resolution and number of
colours that can be displayed.
– Number of pixels used to represent a full screen
– Dependent on number of bits available for each pixel
If only 1 bit, only 2 colours can by displayed
8 bits will allow 256 colours
16 bits (2 bytes) will allow 65,536 colours per pixel
800x600 with 65,536 colours requires approx 1Mb of video RAM
Communicating with the CPU
– Used to transfer data, addresses and control signals to various
components of the computer
– Connect the various registers and internal components of the CPU
– Connect the CPU to main memory and the I/O units
– Because I/O units vary in terms of their speed, mode of operation
and so on, they are not connected directly to the CPU. Each device
will have its own interface unit
Data Transmission – Parallel & Serial
– A parallel bus with 8 lines can transfer 1 byte at a time
– A serial bus only transfers 1 bit at a time.
– Common serial interface is the 25-pin RS232C cable used to
connect an external modem to a PC
– Most mouse interfaces used to be a 9-pin serial interface,
although now they are usually a PS2 connection and
increasingly USB (Universal Serial Bus connection)
USB offers speeds of up to 12 megabit per second
– In serial mode only 1 line is used for data, the other lines are
used for control signals, grounding etc
– Parallel is faster because 8 bits are transferred
– Parallel only available over short distances (2 – 3 metres)
Buffering & Spooling
– Memory used to hold data during I/O transfers to and from I/O
– CPU operates much faster than printer so input and output have to
Once I/O is initiated by CPU, a special I-O channel takes control.
– Many printers will have their own memory buffer
– These speed up communication between devices which operate at
– Output for the printer, for example, may be spooled (written) to disk.
– When the printer becomes free, output will be printed
– This is the method employed on a network.
Installing Hardware Devices
Scanners, printers, mouse, soundcard etc
– When these devices are installed on to a computer system
they usually require a device driver to be installed.
– You may also need to assign a port for a printer
– Most devices can now be installed via Plug and Play on
– A printer driver carries information specific to the printer
model – fonts and control sequences, etc.
– The driver will translate the font and formatting information in
your document into a form that the printer can understand.