Computer Architecture : I/O Interface

Interface is a shared boundary between two separate components of the computer system which can be used to attach two or more components to the system for communication purposes. In computer system, there are special hardware components between the CPU and peripherals to control or manage the input-output transfers. These components are called input-output interface units because they provide communication links between processor bus and peripherals. Input and output devices are not connected directly with CPU, because of the following reasons :

  • CPU working speed is very fast as compared to I/O.
  • CPU is an electronic device whereas I/O are electromechanical device which works at very low speed.

Due to this reason, I/O devices are interfaced to the CPU buses with the help of electronic circuitry called I/O ports. An I/O port is assumed to be made up of device selection logic, bus drivers, data buffers, status registers, control lines etc. The below figure shows the interfacing of I/O devices through I/O ports.

An input device is connected to the processor with the help of the input port. The port is the place used for loading or unloading data. The input device unloads data at an input port. After this the CPU reads the data from the input port. An output device is connected to the CPU with the help of an output port. The CPU unloads data at an output port. After this the output device reads data from this port.

Serial and and Parallel Ports :

Computers possess a few built in interfaces called ports. Peripheral devices are interfaced to the computer through these ports. In Computer system data flows in and out with the help of these ports. Ports are of two types : parallel and serial port.

1. Parallel Port : A parallel port permits the transfer of all the bits of a word at the same time. In parallel data transfer there are multiple lines to connect the peripheral to the port. It is used for high speed peripherals such as disk, tape and printers.

2. Serial ports : A serial port permits the serial data transfer. In serial data transfer one bit of data is transferred at a time. It is used for slow-speed peripherals such as terminals, mouse, modem etc. Printers uses serial interface if they are of low speed.

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