Input/output (I/O)

Hard disks are common I/O devices used with computers.

I/O is the means by which a computer receives information from the outside world and sends results back. Devices that provide input or output to the computer are called peripherals. On a typical personal computer, peripherals include inputs like the keyboard and mouse, and outputs such as the display and printer. Hard disks, floppy disks and optical discs serve as both inputs and outputs. Computer networking is another form of I/O.

Practically any device that can be made to interface digitally may be used as I/O. The computer in the Engine Control Unit of a modern automobile might read the position of the pedals and steering wheel, the output of the oxygen sensor and devices that monitor the speed of each wheel. The output devices include the various lights and gauges that the driver sees as well as the engine controls such as the spark ignition circuits and fuel injection systems. In a digital wristwatch, the computer reads the buttons and causes numbers and symbols to be shown on the liquid crystal display.

Often, I/O devices are complex computers in their own right with their own CPU and memory. A graphics processing unit might contain fifty or more tiny computers that perform the calculations necessary to display 3D graphics. Modern desktop computers contain many smaller computers that assist the main CPU in performing I/O.

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