Bits and Bytes

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Bits and Bytes!

• Concepts of ICT explained

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A computer..?

• Job specification? Desktop publishing, video
  editing, sound editor, internet browser,
  calculates wages......

OUTPUT
INPUT
PROCESSES
A computer accepts Input, Processes it in some
way, then displays or outputs the information.
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Types of Computers

• Mainframe
• Expensive with large storage capacity
• Can cope with very high volumes of transactions
• Typically used by banks, insurance companies,
  government organizations and large corporations
• Hold vast databases of information which can be
  accessed quickly and updated by a large number of
  users at the same time and support a large number
  of peripherals
• Expected to run 24 hours a day, 365 days a year

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The PC/ Personal Computer

• Types Desktop/Laptop or Notebook/ Personal
  Digital Assistants (PDAs)/Palmtop computers
• Laptop - Portable/Own integral screen and
  keyboard/May have own rechargeable batteries or
  require electric power
• Main uses of PCs are as desk-top business
  computers used for word processing, small
  business accounts, financial planning, or as home
  computers.
• Capable of stand alone or networked use, possible
  to link PCs together to share storage
  facilities, printers, or files of information.

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• Network server Administers, supports and
• protects security of a computer network
• Dumb Terminal - An input or output device with
  no processing power of its own,
• Consists of a keyboard, display screen and a
  communication link to a mainframe computer.
• Accepts input from user, displays results,
  processing done by server.
• Intelligent terminal - a terminal which retains
  a program and allows processing of data to be
  carried out without further access to the host
  computer.

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Hardware

• The physical components that make up a computer
  system
• Includes
• monitor,
• keyboard,
• cables,
• memory,
• printer and the case containing the computer
  itself (the processor)

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Software

• Term used to describe the sets of instructions or
  programs that tell the hardware what to do and
  includes the programs which we use on the
  computer e.g. Word processing, games,
  encyclopedia
• Two types of Software
• System Software
• Application Software

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System software

• Manages files and storage, Controls devices,
• Recognizes input, Sends output to screen,
  Communicates with peripherals
• Main piece of systems software is the OPERATING
  SYSTEM.
• Operating systems include DOS, UNIX, Windows 3.1,
  95, 98, 2000, XP.
• DRIVERS Special piece of software to enable
  operating system to control hardware e.g.
  Certain printers require separate drivers,
  compatible with current operating system, to be
  installed before printer will work.

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OPERATING SYSTEM

• Automatically loads when computer is
• switched on, otherwise computer will not work.
• Functions
• Boots up the system , controls input and output
  devices, manages the transmission of data between
  application software, storage device and RAM.
• Translates commands received from the
  applications software word processing programs,
  spreadsheets etc into instructions specific to
  the hardware
• Distributing RAM, controlling input and output
  devices, allowing/preventing access to
  authorised/unauthorised users

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APPLICATION SOFTWARE Generally Applies To
Programs Written For A Particular purpose
e.g. Word, Excel, Powerpoint, Access,
Desktop publishing

• WORD PROCESSING
• A programme specifically developed for the typing
  and production of letters, reports and documents.
• Unlike typewriter, text can be saved and
  modified.

• SPREADSHEETS
• Microsoft Excel - Commonly used spreadsheet
• Excel workbooks - contains
• the file in which work is done and data stored
• Each workbook contains many worksheets
• Each spreadsheet consists of columns down and
  rows across.
• Spreadsheets - largely are used for calculations
  from simple additions to complicated formulae
• Graph feature - range of options used for
  comparisons of data

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DESKTOP PUBLISHING

• A Programme for producing professional-quality
• reports, booklets and magazines.

Publisher provides pre-designed templates for a
wide range of documents newsletters, cards,
banners, flyers, brochures, calendars,
advertisements. Templates can be modified or the
user can create from scratch.

• MICROSOFT ACCESS
• A program that enables creation of and working
  of databases
• MICROSOFT POWERPOINT
• A program that creates visual slides for a
  presentation and handouts for use when addressing
  an audience

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Memory

• RAM (Random Access Memory)
• ROM (Read Only Memory)
• Cache Memory

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Random Access Memory(RAM)

• RAM is temporary, fast memory
• Working memory - holds lists if instructions
  that it is currently working on and handles work
  since last saved
• RAM is volatile and requires a constant supply of
  electric power , data is lost when the power to
  the computer is turned off
• Saving work removes it permanently from RAM to
  disk
• Additional RAM chips can be added by installing a
  memory-expansion card
• The more RAM, the faster the computer operates,
  the more programs that can be open simultaneously
  and the faster they perform
• A certain minimum RAM is required to install and
  run programs
• 64 Mb or 128Mb RAM minimum now required to run
  most programs

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ROM (Read Only Memory)

• A memory that holds data or special instructions
  for computer
• operation, such as starting the computer or
  putting characters on the screen.
• Contents of ROM are permanently fixed when the
  computer chip is made
• Information in ROM remains intact even when
  computer is switched off
• Computer can only read what is in ROM, it
  cannot alter it
• ROM cannot be altered by the computer or
  programmer - the actual content of ROM is fixed
  at the time of its manufacture. ROM can only be
  changed by changing the computer.

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Cache memory

• A special high-speed memory area linked to the
  processor that the CPU can access quickly.
• Frequently used data is stored here saving the
  processor from having to read from the hard disk
  all the time. Allows the CPU to run faster
  because it doesnt have to take time to swap
  instructions in and out of RAM.
• Measured in bytes ranging 128kB - 512kB

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Other forms of memory

• Video RAM (VRAM) used to store display images for
  the monitor.
• Determines how fast images appear and how many
  colours are available.
• Video memory chips are essential when running
  programs that display a lot of graphics.

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Memory Measurement

• Bit Short for Binary Digit-the smallest unit of
  Data that
• the computer can handle. Data is represented by
  on and off
• states of the computers electronic circuitry.The
  binary digit for on is 0 and off is 1.
• Character Combination of bits(0s and 1s) are
  used to represent charactersletters,digits and
  special symbols like, etc.
• Byte A fixed number of adjacent bits that
  represent characters are called a byte-this is
  the amount of memory needed to store one
  character such as a letter or a number.Eight bits
  are used to represent a character.
• Field A collection of related characters.
• Record A collection of fields that relate to a
  single unit is a record.
• File A grouping of related records
• Kilobytes equal to 1024 bytes or characters (KB)
• Megabytes equal to 1024 kilobytes (approx. one
  million bytes (MB))
• Gigabytes equal to one billion bytes (GB)

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Computer Power

• CPU Speed
• The amount of RAM
• Cache memory
• Hard disk size
• Clock speed

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C.P.U.

• The central processing unit is the little chip in
  personal computers that controls everything.

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Hard Disks

• Enable large amounts of data to be stored
• accessed, and read at very high speeds
• Consists of magnetic storage plates encased in a
  hard disk drive
• The computers main storage device holding the
  files for the operating system plus the program
  and data files

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The System Clock

• Every microprocessor contains a system
  clock.Controls how fast the operations within a
  computer take place.
• Processing speeds are expressed in megahertz(MHz)
• The higher the MHZ speed - the faster the
  computer

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Systems Software Utilities

• Utilities are programs that are designed to
  assist with the routine tasks of running a
  computer system
• Examples- programs to copy or delete files,
  rename files, and format new disks
• Text editors (used to write and amend programs)
  and debuggers (used for finding errors in
  programs) also available.

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• Graphical User Interface (GUI)
• Incorporates four elements Windows, Icons, Menus
  
• and a Pointing Device
• Apple Macintosh Finder or Microsoft Window use a
  computerised desktop as the interface between the
  user and the operating system. Pictures or icons
  represent such items as disks, files and
  programs. A GUI has pull-down menus that allow
  the user to select from a predefined list of
  command choices. A GUI uses a mouse to allow the
  user to point at and select the items or commands
  that are required.
• GUI is easy to use icons are self-explanatory a
  lot of similarity between basic functions of all
  Windows-based software.

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Data - Stages 3 stages Input
Processing Output

• Input Data is input into the computer by typing
  on a keyboard or using a scanning device such as
  a barcode reader in a supermarket
• Processing Once data is input it is processed in
  the brains of the computer- (Central Processing
  Unit)
• Output Data can be distributed to users via Soft
  Copy or Hard Copy
• Soft Copy - Temporary, Displayed on monitor,
  Information vanishes once monitor is turned off
• Hard Copy - Permanent, Printed copy on paper,
  acetate or microfilm

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Input devices

• Inputting methods have evolved dramatically over
  the years
• from the earlier use of keyboard, punched cards
  and paper tape.
• Input methods include
• The keyboard
• The mouse
• Trackerball
• Scanner
• Touchpad
• Light Pen
• Joystick
• Voice Input
• Graphics pad
• Magnetic disk and tape input
• Document readers
• Web Cam
• Digital camera

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• Keyboard is the slowest means of input
• Most used input device
• Its familiar
• Easy to operate
• Mouse
• Many different types including cordless
• Gives fine conrol over use of applications
• Access to menus on Rightclicking
• Tracker ball (track ball)
• A pointing device which you rotate to move the
  mouse cursor commonly found on notebook
  computers

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• Scanners
• Scanner - used as a means of capturing an
  existing two-dimensional image - a drawing or a
  photograph that could not be input using a
  graphics
• pad
• image scanners divide a picture into a matrix of
  tiny dots each of which is stored in a file in
  the computer.
• It is then possible to use this file with an
  existing text file in order to combine pictures
  with text as in a newspaper
• Optical Character Recognition (OCR)
• Enables information to be automatically read
  from a printed document
• OCR scanners can recognise typed and neatly
  handwritten material.
• OCR is used by organisations like gas,
  electricity and credit card companies, all of
  whom need to process large numbers of similar
  documents in a short space of time.
• Video scanners
• The video scanner uses a video camera to capture
  an image for processing either of an existing
  two-dimensional picture or of a three dimensinal
  object
• Video scanners will generally offer a higher
  resolution than image scanners

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• Touch screens (touch pads)
• Designed to avoid the use of a computer keyboard,
  the user will simply touch the appropriate icon
  or other reference on the screen.
• Action will be sensed by the computer, and the
  option chosen will be acted upon.
• Light Pens
• Device used in conjunction with special hardware
  and software that shines light on to a VDU screen
  to indicate a choice from a menu or to input a
  location in graphics work
• In libraries, bar codes are read by using a light
  pen or wand

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• Joysticks
• Input device for a microcomputer.The stick as it
  moves (usually in one of eight directions) is
  able to control the movement of a shape on the
  screen. Sometimes there are 2 joysticks enabling
  a screen game to be played by 2 players.
• Voice Input
• Possible to programme a computer to respond to
  voice commands
• Present voice recognition systems need to be
  trained to cope with a particular voice
• Must be restrained if the user gets a cold or has
  a sore throat

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• Graphics pad
• Used to input graphic image to a computer
• Freehand images can be input by drawing with the
  stylus
• on the bed of the pad.
• Existing drawings may be traced by the stylus on
  the bed alternatively they may be input by using
  a cursor similar to a mouse
• The cursor is positioned in turn over the key
  points on the drawing and one of the buttons on
  it is pressed
• The computer records these points and joins them
  together as necessary to define the computer
  image.
• When used to input existing drawings, graphics
  pads may also be called digitisers.
• They are used by architects to design buildings,
  and as part of CAD systems in engineering

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Magnetic disk and tape input

• Both widely used for the storage of computerised
  information
• A computer storage device that looks rather like
  an LP record that has the same magnetic coating
  as an audio
• Information is recorded onto and read from the
  surface of the disk in much the same way as a
  domestic cassette tape recorder is used to record
  and play back music
• Magnetic tape is the computer equivalent of the
  reel-to-reel tapes found on professional tape
  recorders
• Data can be transferred from magnetic disk or
  tape far faster than it can be input from any
  other device
• Speeds of input from magnetic tape or disk are
  termed data transfer rates
• Magnetic ink character recognition (MICR)
• Enable the fast and efficient clearing of cheques
• Characters are printed in a special ink that can
  be magnetised to give off a unique magnetic field
  that enables each character to be read
• Used by the banks as a way of speeding up the
  cheque clearing system- input speeds can be
  anything up to 2000 cheques a minute

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Card Readers

• A device that reads information held in the form
  of
• a magnetic strip on a plastic card e.g. Credit
  card,
• ATM card
• Bar-code readers
• An arrangement of vertical bars and spaces that
  can be read by an optical scanner and used as a
  means of identifying products or stock items
• Seen on most products purchased in supermarkets,
  inside library books, and on such items as
  freezers and computers. In supermarkets, each
  product carries a unique bar code that can be
  used both to calculate the size of the bill at
  the point-of-sale (POS) terminals (or check-outs)
  and for stock control.
• System operates from a central computer which
  controls the POS terminals.
• When shoppers goes through a check-out, each item
  is passed over the scanner which reads the bar
  code and refers to the central computer for the
  description and price.
• Information is relayed to the check-out, where it
  is displayed on a customer panel printed on a
  receipt. Stock level for the item purchased will
  be reduced , providing management with up-to-date
  stock information and enabling more efficient
  stock control and ordering.

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• Document readers
• Can be read by humans as well as by machines
• Used where there is a need to be able to process
  large volumes of similar documents, like cheques
  or gas bills Automated processing of cheques
  quickly
• Computer marking of multiple choice answer sheets
• Reading of large volumes of credit card payment
  slips
• Web Cams
• Allows two way communication including sound and
  video as well as text
• Digital cameras
• Images are stored digitally in memory in camera
• Pictures can be transferred to computer and
  edited digitally

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Computer Output

• Output Once the data has been processed,
  information can be distributed to users.
• Computer output can take the form of a display on
  a screen,
• a print-out, or transfer of information on to a
  magnetic tape or disk.
• Most output falls into one of two categories
  hard copy or soft copy.

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• Hard copy is output in a permanent or touchable
• form e.g. printed form such as on paper or
  microfilm. May be produced either on separate
  sheets or on continuous stationary taking the
  form of folded and perforated lengths of paper
• Soft copy is information that is displayed
  visually on a screen or monitor - temporary once
  the monitor is turned off or new information is
  required, the old information vanishes.
• Also can be in audio form, as in speech or music

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• Visual output
• Most common form of soft-copy output is
  information displayed on a screen or cathode-ray
  tube(CRT)
• The VDU enables a user to input information to a
  computer by using a keyboard, mouse or touch
  screen facilities and to view output on a CRT
• Two factors limit the use of the CRT its weight
  and the amount of power it consumes
• Liquid-crystal displays (LCDs) similar to those
  found on some digital watches are both light and
  economical enough to be widely used for portable
  computers

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Computer output on microfilm (COM)

• As an alternative to printed output, another form
  of hard copy is computer output on microfilm or
  microfiche
• COM is the recording of what would otherwise be
  printed output direct in reduced form on to
  either rolls or sheets of photographic film
• Microform can store documentary information with
  textual and graphical content
• Structure can be either microfilm (a continuous
  reel) or microfiche (a grid pattern)
• Microform reduces storage space requirements by
  approximately 95 of that required by paper
  documentation

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Audio output Covers the range from the simple
beep to full speech synthesis. Speech
synthesis is the production of a sound
corresponding to spoken words and it is of great
use where a user is unable to look at a CRT or is
occupied with another. Computer Speakers Have
the same function as hi-fi music speakers used in
the home stereo systems. Differ from conventional
speakers in that they are self amplified and
magnetically shielded. Most speakers are AC
powered and have separate volume tone
controls.
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Printers

• Two most common types of printers
• Inkjet Printers
• Laser Printers
• Also third category - Matrix Printers

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• Ink-jet printers
• Work by using tiny jets to spray ink at high
  speed onto the paper
• Forms characters by projecting the ink from the
  small ink nozzles (the same way as by the
  dot-matrix printer) on to the paper - for this
  reason are termed a non-impact printer.
• Ideal for low volume printing with high quality
  where speed is not priority
• Major advantage over a dot-matrix printer is low
  level of noise
• Laser printers
• Shares the same image-printer technology as the
  photocopier.
• Print image is produced by a laser beam which
  scan across the print drum, line for line as the
  print cylinder rotates.
• High quality at high speed

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Dot-matrix printers

• Gets name from way in which a number of needles
  in the print head are used to print text as a
  series of dots using a carbon ribbon.
• The more pins the print head has, the higher the
  quality of print
• The speed at which a dot-matrix printer is able
  to operates depends on which typeface is being
  printed
• Typical speeds may range between 40 and 500 c.p.s
  according to the print quality.
• Noisy and not high quality
• Suitable for high volume/low quality printing
  e.g. printing company payslips
• Widely used as a micro-computer peripheral

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• Thermal printers
• Use heat to transfer the image from the print
  head to the paper.
• Text and images are made up from a series of
  dots, in common with
• other matrix printers, but with this process the
  print head may be either a fixed array of thermal
  elements
• Daisy-wheel printers
• This printer takes its name from a flat disc with
  a number of stalks or petals radiating from its
  centre each of which has a character at its tip.
• Daisy wheel rotates at high speed and the petals
  are pushed on to a ribbon which, in turn
  transfers the characters to the paper.
• Line printer
• Gets its name from the way in which it prints a
  line of text at a time.
• Two types- chain printer and the drum printer.
• Main feature is their speed, the fastest printing
  text at around 5000 lines per minute. This is
  achieved by hitting the paper against the
  character and printer ribbon.

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Graph plotters

• An output device similar to a printer but
  normally
• allows printing of larger images
• The graph plotter is a specialist device designed
  to produce high-quality pictures and designs.
• Unlike matrix printers, a graph plotter
  reproduces the human action of drawing by using a
  pen.
• Widely used by architects and designers of all
  kinds
• Two types of graph plotter- flatbed and drum

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Peripherals

• A Peripheral is any device that is connected to
  and controlled by a computer but external to the
  CPU etc.
• Peripherals include
• Printers
• Loudspeakers
• Scanners
• Digital camera
• Microphone

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Storage

• Primary and Secondary Storage
• The Term primary storage (main memory) refers to
  RAM
• Secondary storage is auxiliary storage - any
  storage device designed to retain data and
  instructions (programmes) in a relatively
  permanent form.
• Secondary storage is non-volatile, meaning that
  saved data and instructions remain intact when
  the computer is turned off.

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CD-ROM Compact Disk Read
Only Memory

• Widely used for reference material and training
  purposes, has huge storage capacity
• Ideal for storing all forms of images including
  video sequences which take large amounts of
  storage space
• Not used for storage of documents which require
  regular updating.
• Speed of CD ROM drive is regularly being improved
• Standard CD-ROMS can only be written to once,
  CD-RW disks can be written to more than once
• A CD-writers/burner used to record or copy to a
  CD
• CD-ROMS now being over taken by DVDs (Digital
  Versatile Disks)

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Diskettes

• A diskette or floppy disk stores data and
  programs as magnetised spots
• The disk is contained in a plastic case to
  protect it
• Diskettes are sometimes called floppy because
  the disk within the envelope or case is flexible,
  not rigid.

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Zip Disk/Zip Drive

• A removable disk, capacity of 100 - 250 MB
• Can be internal or external
• Popular for keeping backups and for
  transferring large files between computers

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Electronic Commerce

• E-Commerce a generic term for all forms of
  business
• transactions on the Internet. The potential to
  advertise and sell ones product via a web site
  to mass audiences has limitless appeal.
• The 7 most popular buys on-line are Books, CDs,
  Travel, Music, Electronics, Computer hardware and
  Clothing. Books sales on-line phenomenal growth
  eg. Amazon.com. CDs from America half the local
  price however, delivery cost must be considered.
• lastminute.com specialise not only in cheap
  travel but also in occasional purchases like cars
  or mobile phones.
• Shopping on-line using a credit card is
  relatively safe. It is advisable to use
  e-commerce sites that keep your card details on a
  secure server so you dont have to send them each
  time you make a purchase. Ensure that your
  browser is set up for secure connections to the
  internet. A padlock displaying on the status bar
  of the program when you connect to a secure
  server indicates that your data is secure.

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Requirements for connecting a Computer to the
internet

• A computer with a fast processor, 16-128MB of
  RAM, up to 100MB of free hard disk.
• A Modem (unless broadband is available)
• A Telephone line
• An Internet Service Provider (ISP). Modem via the
  telephone line will link to the internet through
  the computer system of the service provider.
• Connection Software

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• Data Protection Act 1984
• Safeguard the privacy of the individual
• Legislation protects personal data handled in
  computers
• Aim to control the immense potential for misuse
  of information that arises when personal data is
  stored in computers.
• - Once data has been transcribed from paper
  files into a form that is easily readable and
  accessible by computers, it is an inexpensive and
  easy task for the data to be extracted from one
  record and correlated with personal data
  concerning the same person from another file -
  infringement of privacy.

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• Requirements of organisations that maintain
• personal records on computers
• To declare and/or register the use for which data
  is stored
• Must make information available to those
  authorised to receive without undue delay or
  inefficiency
• Provide the data subject with a right of access
  to data concerning himself on their computer
• Keep information secret from those not so
  authorised in such a way that the cost of
  unauthorised disclosure would exceed the value of
  the information to the illegitimate recipient.
• Maintain a prescribed minimum level of electronic
  and physical security in their computer
  installations - System may involve physical
  security (safes, locks entry cards) for access to
  disks and passwords and also the technique of
  cryptography and authentication.
• Not to transmit personal data to any organisation
  that does not have similar controls over misuse
  of data
• The OECDS has also drafted a convention of
  similar effects

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Repetitive strain injury (RSI)

• Also known as repetitive motion injury and
  cumulative trauma disorder is
• the name given to a number of injuries resulting
  from fast, repetitive work
• RSI causes neck, wrist, hand, and arm pain.
• RSI problems can result from prolonged computer
  keyboard use
• An RSI called carpal tunnel syndrome is
  particularly common among young people who use
  computers and certain types of scanners
  intensively. This syndrome involves damage to
  nerves and tendons in the hands.

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• RSI Causes
• Repetition and duration Prolonged, constant and
• repetitious movements such as typing irritate
• tendons and nerve casings, causing them to
  swell.
• Force The harder you hit the keys, the more
  likely to suffer injury.
• Joint angle Flexing raising, or twisting hands
  to reach the keys constricts the carpal tunnel.
• Prolonged constrained posture Holding any
  position without moving puts excessive strain on
  muscles and tendons.
• Left untreated, this syndrome can cause atrophied
  nerve damage.
• To avoid RSI
• Frequent short rest breaks.
• Plenty of sleep and exercise, maintain
  appropriate weight, sit up straight and learn
  stress- management techniques.

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Health and Safety Computer work environment

• Prolonged use of computers can cause
  eyestrain,muscular strain, changes in colour
  perception, back and neck pain,stomach aches, and
  nausea.
• To reduce such physical problems,time spent at a
  VDU be reduced to a maximum of two hours per day
  of continuous screen work.
• Periodic rest breaks be granted.
• Steps taken to reduce or alleviate glare produced
  by overhead fluorescent lighting-glare reduction
  screens should be available as required by the
  employee.

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Systems Development

• Process by which a computerised information
  system is created
• Stage 1 choosing the information system to be
  computerised
• Stage 2 Feasibility study
• Stage 3 Full analysis of the system to be
  computerised
• Stage 4 Designing how the computerised system
  will work
• Stage 5 Writing the programs
• Stage 6 Implementing the new system
• Stage 7 Maintaining the System

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Computer networks

• Connecting a computer to other computers in same
  building or in another part of the world
• Share Hardware eg. Printers
• File - Sharing
• E-mail / Data exchange

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• Computer Based Training (CBT)
• Advantages
• Flexibility of studying whenever
• Can work at own pace
• Disadvantages
• No regular routine
• Student needs to be strongly motivated or highly
  disciplined
• Cannot consult a tutor
• No interaction with other students

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• Multimedia
• Global term for the developing computer
  technology that
• can combine text, graphics, hi-fi sound,
  animation, and
• full motion video in a single high-resolution
  display
• Made possible by the common use of digital
  recording of text,
• graphics, sound, and video, coupled with the
  increased
• processor speeds required to handle large video
  files
• Multimedia Applications
• Training Cheaper alternative to traditional
  techniques for staff induction, training in new
  procedures and general management training
• Architectural Visualisations CAD system
• Advertising/promotions Logos, trademarks, and
  storyboard outlining Advertising can be created,
  animated, and given a sound track using
  multimedia authoring software
• Home Entertainment include interactive cartoons,
  games, and an interactive multimedia world atlas

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E-MAIL

• Disadvantages
• Carries of viruses
• Unsolicited e-mails Spam

• Advantages
• Quick inexpensive immediate contact can be made
• Using the cc or bcc facility numerous
  communications can be distributed simultaneously
• Attachment facility provides the means of
  forwarding long files

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• Viruses
• A virus is a program code written to replicate
• by attaching copies of itself to other objects
  within the system, normally also having a
  detrimental effect. Usually lie dormant for a
  while, then establish their presence by
  displaying a message, stopping the computer or
  deleting a file.
• These destructive programs infect a computer
  similar to the way biological viruses infect
  people.
• Problems may range from displaying messages
  through loss of service to corruption or complete
  destruction of data
• A program virus will seek out and copy itself
  into other program files whenever a previously
  infected program is run.

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• Virus Protection
• To protect, purchase your software only from
  reputable dealers
• Run an anti-virus utility and back up hard drive
• Greatest carriers of viruses are disks which are
  illegally copied programs, especially games
• Backup
• A copy you make of a file in case the original
  file gets destroyed or corrupted
• Use backup command of your computer
• Can back up files to floppy disks, a tape drive
  etc

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Precautions and power failure

• Use special anti-power surge extension leads on
  all computer sockets
• Use UPS (Un-interruptible Power Supply)
• Have backup of files