• In addition to the processor and a set of memory modules, the third key element of a computer system is a set of input-output subsystem referred to as I/O, provides an efficient mode of communication between the central system and the outside environment.
  • Programs and data must be entered into computer memory for processing and results obtained from computations must be recorded or displayed for the user.
  • Devices that are under the direct control of the computer are said to be connected on- These devices are designed to read information into or out of the memory unit upon command from CPU.
  • Input or output devices attached to the computer are also called peripherals.
  • Among the most common peripherals are keyboards, display units, and printers.
  • Perhaps those provide auxiliary storage for the systems are magnetic disks and tapes.
  • Peripherals are electromechanical and electromagnetic devices of some complexity.
  • We can broadly classify peripheral devices into three categories:
    • Human Readable: Communicating with the computer users, g. video display terminal, printers etc.
    • Machine Readable: Communicating with equipments, g. magnetic disk, magnetic tape, sensor, actuators used in robotics etc.
    • Communication: Communicating with remote devices means exchanging data with that, e.g. modem, NIC (network interface Card) etc.

                                     

                                             Fig: Block diagram of Peripheral device

  • Control signals determine the function that the device will perform such as send data to I/O module, accept data from I/O module.
  • Status signals indicate the state of the device e. device is ready or not.
  • Data bits are actual data transformation.
  • Control logic associated with the device controls the device's operation in response to direction from the I/O module.
  • The transducer converts data from electrical to other forms of energy during output and from other forms to electrical during input.
  • Buffer is associated with the transducer to temporarily hold data being transferred between the I/O module and external devices e. peripheral environment.

Input Device


  • Keyboard
  • Optical input devices
    • Card Reader
    • Paper Tape Reader
    • Optical Character Recognition (OCR)
    • Optical Bar code reader (OBR)
    • Digitizer
    • Optical Mark Reader
  • Magnetic Input Devices
    • Magnetic Stripe Reader
    • Magnetic Ink Character Recognition (MICR)
  • Screen Input Devices
    • Touch Screen
    • Light Pen
    • Mouse
  • Analog Input Devices

Output Device


  • Card Puncher, Paper Tape Puncher
  • Monitor (CRT, LCD, LED)
  • Printer (Impact, Ink Jet, Laser, Dot Matrix)
  • Plotter
  • Analog
  • Voice