Key-to-disk system - many data entry operators key in data from source documents. Batch data stored on disk. Source data passed to second data entry operator who, in verify mode, enters data a second time. Any discrepancy causes machine to beep. Data either downloaded to main computer over communications link or transferred to magnetic tape and taken to main computer room.

Light pen - uses light sensor to move characters or part of graphics

• encoded with up to 220 characters of data
• characters are easy to copy -> fake magnetic stripe cards

Smart cards - contain 1mm square microprocessor

Optical Mark Recognition (OMR) - detects marks made in pre-set positions on form

Hand-held input devices - e.g. for reading gas / electricity meters - displays customer name, address and location of meter - at end of day all readings are downloaded by communication link to main computer for processing

Digitiser (graphics tablet) - data can be transferred to a computer

Dot matrix printer - impact printer (pins strike ribbon)

• for NQL (near letter quality) each line is printer twice
• noisy (need cover in office)
• colour is not very good quality

Ink jet printer (fires drops of ink at page by boiling in microscopic tube and letting steam eject droplet)

• compact
• quiet
• slow (average 3 pages per min)
• colour can cost up to 75p per page
• resolution almost as good as laser printer
• ink may smear and paper may buckle

Laser printer (toner transferred to page then fused onto it by heat and pressure)

• 10 pages per minute
• virtually silent
• £75 per cartridge (5000 copies)

• produces high quality line drawings such as building plans and electronic circuits
• 2 types - pen (vector plotters) and penless (raster plotters)
• pen plotters use point-to-point data
• penless plotters include electrostatic, thermal and laser (for higher densities)

• 3 basic attributes - size, colour, resolution
• fixed amount of RAM to store image being displayed - determines resolution and max. no. of colours that can be displayed
• resolution determined by no. of pixels used to represent full screen image
• no. of colours displayed determined by no. of bits per pixel (2 bits -> 4 colours, 8 bits -> 256 colours)
• if you have a higher resolution you can't have as many colours

Primary storage - RAM (computer's main memory) - volatile

• magnetic tape
• magnetic disks
• CD-ROM
• microfilm

• 1.44MB
• flexible plastic disk coated in metal oxide
• two surfaces each with 80 concentric circles called tracks
• tracks near centre store same amount of data as outer tracks

• one or more disk platters permanently sealed inside casing
• each surface has its own read-write head
• capacity of between 2GB and 100GB

• several hard disks
• fixed or removable
• data stored in concentric tracks
• cylinder:- all tracks accessible from one position of read-write head
• data recorded cylinder by cylinder to minimise access time

• data recorded in 'frames' across the tape
• cheap and convenient medium for backup

• store around 680MB data
• laser beam burns holes into surface of disk -> read-only
• single spiral track divided into sectors

WORM disks (Write Once, Read Many) - optical laser disks

• integrate optical and laser technology to enable read and write storage
• 5¼" disk can store 1GB
• at the moment are expensive, slow and unreliable