Computer Architecture : I/O Modules

A computer system has three major components : CPU, the memories and I/O devices such as printers, scanners and modem. Each component interface to the system bus and control various peripheral devices. The computer will be no use if it is not communicating with the external world. A computer must have a system to receive information from outside world and must be able to communicate results to external world. Thus, a computer consists of an I/O (input-output) system. This system includes two components, The first one is I/O devices and the second one is I/O module, which not only connects an I/O device with the system bus, but plays a very crucial role in between. A device which is connected to an I/O module of computer is called a peripheral device.

The Input/Output module ( I/O module ) is normally connected to the computer system on one end and one or more Input/Output devices on the other. An I/O module is needed because of :
  1.  Diversity of I/O devices make it difficult to include all the peripheral device logic into CPU.
  2. The I/O devices are usually slower than the memory and CPU. Therefore, it is not advisable to use them on high speed system bus directly for communication purpose.
  3. The data format and word length used by the peripheral may be quite different than that of a CPU.

An I/O module is a mediator between the processor and an I/O devices. It controls the data exchange between the external devices and main memory or external devices and CPU registers. An I/O module provide an interface internal to the computer which connects it to CPU and main memory and an interface external to the computer connecting it to external device or peripheral. The I/O module should not only communicate the information from CPU to I/O device, but it also coordinate them. 

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