Input-Output Organization In Computer System

Input-Output Organization

The input/output subsystem  proves an efficient mode of communication between the central system and outside environment. Data and programs must be entered into the computer memory for processing. The result of processing must be must be recorded or displayed for the user.

Peripheral devices

Any input/output devices connected to the computer are called peripheral devices.

Input Devices

• –  Keyboard
• –  Card Reader
• –  Digitizer
• –  Screen Input Devices
• –  Touch Screen
• –  Light Pen
• –  Mouse

Input-Output Interface

• Provides a method for transferring information between internal storage (such as
• memory and CPU registers) and external I/O devices
• Resolves the differences between the computer and peripheral devices
  • Peripherals – Electromechanical Devices, CPU or Memory – Electronic Device
  • Data Transfer Rate
    » Peripherals – Usually slower
    » CPU or Memory – Usually faster than peripherals
•  Some kinds of Synchronization mechanism may be needed
•  Unit of Information» Peripherals – Byte, Block, …» CPU or Memory – Word
•  Data representations may differ

I/O bus and interface modules

Input/output bus from the processor is connected to all peripheral interfaces. To communicate with a particular device, the processor places a device address on the address lines. Each peripheral has an interface module associated with its interface. Functions of an interface are as below:

• –  Decodes the device address (device code)
• –  Decodes the I/O commands (operation or function code)
• –  Provides signals for the peripheral controller
• –  Synchronizes the data flow and

Supervises the transfer rate between peripheral and CPU or Memory