Input/output

In <a href="/facts/Computing/Kghtm9fX">computing</a>, input/output (I/O, i/o, or informally io or IO) is the communication between an information processing system, such as a <a href="/facts/Computer/SQe1aK05">computer</a>, and the outside world, such as another computer system, peripherals, or a human operator. <a href="/facts/Information/3LdrzXtJ">Inputs</a> are the signals or data received by the system and outputs are the signals or <a href="/facts/Data_(computing)/cPjfFHph">data</a> sent from it. The term can also be used as part of an action; to "perform I/O" is to perform an <a href="/facts/I/O_scheduling/4WvHrePc">input or output operation</a>.
I/O devices are the pieces of <a href="/facts/Hardware_(computing)/8jSjsCNv">hardware</a> used by a human (or other system) to communicate with a computer. For instance, a <a href="/facts/Computer_keyboard/MczF9LIS">keyboard</a> or <a href="/facts/Computer_mouse/fJpa1tUE">computer mouse</a> is an <a href="/facts/Input_device/TXYLUkux">input device</a> for a computer, while <a href="/facts/Computer_monitor/NRaTDFHc">monitors</a> and <a href="/facts/Computer_printer/PnDF2QuF">printers</a> are <a href="/facts/Output_device/zQt81QMq">output devices</a>. Devices for communication between computers, such as <a href="/facts/Modem/9H0Xwtq0">modems</a> and <a href="/facts/Network_card/wyf5FR29">network cards</a>, typically perform both input and output operations. Any interaction with the system by an interactor is an <a href="/facts/Input_(computer_science)/CulgMb3T">input</a> and the reaction the system responds is called the output.
The designation of a device as either input or output depends on perspective. Mice and keyboards take physical movements that the human user outputs and convert them into input signals that a computer can understand; the output from these devices is the computer's input. Similarly, printers and monitors take signals that computers output as input, and they convert these signals into a representation that human users can understand. From the human <a href="/facts/User_(computing)/zQRzG0KG">user</a>'s perspective, the process of reading or seeing these representations is receiving output; this type of interaction between computers and humans is studied in the field of <a href="/facts/Human%E2%80%93computer_interaction/EkmIxGCx">human–computer interaction</a>. A further complication is that a device traditionally considered an input device, e.g., card reader, keyboard, may accept control commands to, e.g., select stacker, display keyboard lights, while a device traditionally considered as an output device may provide status data (e.g., low toner, out of paper, paper jam).
In computer architecture, the combination of the <a href="/facts/Central_processing_unit/Jxp1bqMV">CPU</a> and <a href="/facts/Main_memory/wPHKFpdx">main memory</a>, to which the CPU can read or write directly using individual <a href="/facts/Instruction_(computer_science)/8p8vwUeE">instructions</a>, is considered the brain of a computer. Any transfer of information to or from the CPU/memory combo, for example by reading data from a <a href="/facts/Disk_drive/hnsXRb5X">disk drive</a>, is considered I/O. The CPU and its supporting circuitry may provide <a href="/facts/Memory-mapped_I/O/PmLNFq01">memory-mapped I/O</a> that is used in low-level <a href="/facts/Computer_programming/QmSsFnu0">computer programming</a>, such as in the implementation of <a href="/facts/Device_driver/rDYnHU1G">device drivers</a>, or may provide access to <a href="/facts/Channel_I/O/vDBtN2wQ">I/O channels</a>. An <a href="/facts/External_memory_algorithm/sCcj8M8o">I/O algorithm</a> is one designed to exploit locality and perform efficiently when exchanging data with a secondary storage device, such as a disk drive.

Input/output open-in-new

Input/output