The Computer  an electronic data processor

Computer Systems  many systems have this structure

Computer Hardware –hardware is anything tangible :  Central Processing Unit –this is inside the main box  Peripherals –these are devices attached to the CPU

Peripheral Devices  input devices –allow data to be entered into the computer  backing storage devices –allow data to be stored for processing  output devices –allow data to be output from the computer

INPUT DEVICES  Keyboard  Mouse  Joystick  Trackerball  Light Pen  Graphics Tablet  Bar Code Reader  Mark Sense Reader  Optical Scanner  Magnetic Ink Character Reader

Keyboard

Keyboard  ideal for alphanumeric data entry  Letter keys : text (word processing)  Number keys : spreadsheets)  Function keys : shortcuts  Cursor Keys : menu choice  Modifier keys : Shift, Alt, Ctrl  NOT ideal for graphics

Mouse

Mouse  Ideal for GUI  ball transmits XY movement  buttons allow selection  NOT alphanumeric data entry

Joystick

Joystick  Ideal for games  XY axis sensors for movement  digital (on / off) : cheap but jerky  analogue : expensive but smooth  buttons allow selection  NOT alphanumeric data entry

Trackerball –effectively an ‘Inverted mouse’  ideal for portable GUI  XY sensors detect ball movement  buttons allow selection

Light Pen

 Direct screen positioning for GUI  button for selection  photosensor detects light spot on VDU  screen position is calculated

Graphics Tablet

 Used in Computer Aided Design  Allows digitising of images  Ideal for GUI

Bar Code Reader  Data capture in shops and libraries  laser beam shines on to bar code  white bars reflect light to photosensor

Mark Sense Reader  Fast, specialised data capture  turnaround documents required  allows simple manual data entry  brushes passed over document  pencil mark conducts electricity

Optical Scanner

OCR

OCR  Data capture direct from writing  specialist fonts : gas meter readers  typed documents read into text files  hand written post codes deciphered

MICR - cheques

Magnetic Ink Reader  Secure data capture for banks  cheques are turnaround documents  data read by humans and machine  cannot be forged  can be read over patterned cheques

OUTPUT DEVICES  Visual Display Unit  Dot Matrix Printer  Daisywheel Printer  Bubblejet Printer  Laser Printer  Plotter  Voice Output

Visual Display Unit

Dot Matrix Printer

Daisywheel Printer

Bubblejet Printer

Laser Printer

Plotter

BACKING STORE  Floppy Disk  Hard Disk  Magnetic Tape  WORM  CD ROM

Floppy Disk

Hard Disk

Magnetic Tape

WORM  Write Once Read Many  650MB storage  Expensive

CD ROM

 Compact Disc Read Only Memory  650MB capacity  Read Only