Unit 2
Hardware Devices

Input Devices

Optical Character Recognition (OCR)

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.

Mouse, joystick, touch screen

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

Magnetic Ink Character Recognition (MICR)

Magnetic stripe

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

Output Devices

Dot matrix printer - impact printer (pins strike ribbon)

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

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


Visual Display Unit (VDU)

Storage Devices

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

Secondary storage

3½" Floppy disk

Hard disks for microcomputers

Hard disks for minis and mainframes

Magnetic tape


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

Magneto-optical disks