Computer Arechitecture | I/O Organization : External Devices

I/O operations are accomplished through external devices. The External devices provides a means of exchanging data between the external environment and the computer. An external device attaches to the computer by a link to an I/O module. An external device linked to an I/O module is called peripheral device or peripheral.

The External Devices can be categorized as :
  1. Human Readable : The human readable external devices are suitable for communicating with computer user. For example - video display terminals and printers.
  2. Machine Readable: These are suitable for communicating with equipment. For example - sensor, actuators used in robotics application.
  3. Communication : These are suitable for communicating with remote devices. They may be human readable device such as terminal and machine readable device such as another computer.

The below figure shows the Block Diagram of External Device.


The interface to the I/O module is in the form of control, data and status signal. The control signal determines the function that the device will perform. For example send data to I/O module (READ or INPUT), receive data from I/O module (WRITE or OUTPUT), report status or perform some control function such as position a disk head. The Data signal send or receive the data from I/O module. Status signal indicates the status of signal (READY/NOT READY). Control logic associated with the device controls on specific operation as directed from I/O module. The transducer converts the data from electrical to other form of energy during output and from other forms of electrical during input. Buffer is associated with transducer to temporarily hold data during data transmission from I/O module and external environment. Buffer size of 8 to 16 bits is common.





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