11.4 Software - Nature_ Capabilities and Limitations

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Nature, Capabilities and Limitations
Categories of Software

 3 general categories :-
   General Purpose
           Applications software
 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
        Systems Software
 Operating systems
 Utility programs
 Programming language
 Performance monitoring software
 Communications software
     General purpose software
   Includes all common application packages such
    –   word processing
    –   desktop publishing
    –   spreadsheet
    –   database
    –   computer-aided design (CAD)
    –   presentation graphics
            Integrated packages
 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
                  Software suites
 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
          Lotus SmartSuite
          Corel
           Generic or Specific?
   Generic software
    – 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
   Specific software
    – 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
            Generic Software
   Application packages that are used to
    perform operations that are an integral part
    of day-to-day business operations.
                Word processor
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
       package’s dictionary.
– 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’
              Spreadsheet features
   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
 Use functions
    – 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;
   Write macros
    – to automate common procedures;
   Create templates
    – 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
   ??
           Presentation Graphics
   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
       Application Generators
   A piece of software that allows users to
    generate their own applications without
    having to do much programming e.g.
    Paradox database software.
         Report Generators

 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
                Web Browser
   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.
Operating Systems
             Systems software
   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
         Operating Systems
   DOS             OS2
   Windows 3.1     Unix
   Windows 9x      Linux
   Windows ME      MacOS
   Windows NT
   Windows 2000
   Windows XT
Functions of an operating system
  Memory management.
 Resource allocation and scheduling
 Backing store management
 Interrupt handling
 Allowing a user to communicate with the
                  Utility programs
   Virus checkers
    – 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
Also Specifies:
 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
    Command-driven interface
          e.g. DOS
 The user has to type in commands in exactly the
  correct syntax to perform any operation
 Experienced users may be able to perform
  operations faster
  using DOS than by
  using WIMP GUI
                    Windows 3.1

   DOS with WINDOWS system

   Microsoft GUI

   Allows
            Windows 9x
 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
   UNIX
    – 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)
   Linked object
    – 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
   Embedded object
    – 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
  drawing package
 You’re doing a research assignment and want to
  download articles from the Internet on ‘Computers
  and Dolphins’
 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
             Evaluating software
   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
      benchmark tests.
           Software Reliability
   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,
      multi-user systems.
Storage Devices
     Primary & Secondary Storage
   Primary Storage
    – Volatile storage, such as RAM, is primary storage
    – All contents lost when machine switched off
    – Good practice to make regular back-ups
   Secondary Storage
    – Non-volatile, more permanent storage for software and
      data files
    – For example:
          Magnetic Tape, Magnetic Disks, CD-ROM, microfilm
                     File Processing
 Method usually depends upon whether every record
  needs to be processed.
 Sequential Processing
    – Every record has to be read. Typically used in a payroll
   Random Processing
    – 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
       called tracks.
      Tracks are divided into sectors when disk is formatted
                        Hard Disks
   PC
    – 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
   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
               Magnetic Tape

 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
                    Other Devices
   CD-ROM
    – 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
                      Other Devices
   Magneto-Optical Disks
    – 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.
   Microfiche
    – 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
Input Devices
          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
  data set
 Supervisor can see all operators data entry
  speeds and number of errors!
Key to Disk (2)
 Used by banks for cheque processing
 Advantages
    – 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
    bar codes?
      Other uses for Bar Codes
   Warehousing
    – bar coded containers of raw materials are stored in racks of
      bins which are also bar coded.
   Medical
    – bar codes used to identify blood and other samples.
   Libraries
    – used to record loans and track stock.
   Banking, insurance and local government
    – for document control and retrieval.
            Any Others?
 Magnetic Stripe
 Smart Cards
 ????
Output Devices
   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
   Dot Matrix
    –   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
   Inkjet Printer
    – Very popular – often bundled with PC
    – Cheap with very good resolution, particularly on
      special papers
    – 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
   Laser 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
           Maps
           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.
 Resolution
    – Number of pixels used to represent a full screen
   Colours
    – 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
   Buses
    – Used to transfer data, addresses and control signals to various
       components of the computer
   Internal Bus
    – Connect the various registers and internal components of the CPU
   External Bus
    – Connect the CPU to main memory and the I/O units
   Interface 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
   Buffers
     – 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
       controlled independently
             Once I/O is initiated by CPU, a special I-O channel takes control.
     – Many printers will have their own memory buffer
   Spoolers
     – These speed up communication between devices which operate at
       different speeds
     – 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
        Windows systems.
    –   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.

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