iO

IO, short for input/output, is a general term for the communication between a computer system and its environment. This encompasses the transfer of data to and from internal components, peripherals, storage devices, networks, and other systems. In computing, I/O performance is a key factor in overall system responsiveness and throughput.

IO devices are categorized as input devices (for example keyboards, mice, scanners, microphones) and output devices (monitors, printers, speakers). Some devices are bidirectional, such as network interfaces and most storage drives, handling both input and output operations.

IO pathways are implemented through hardware buses and controllers, plus software support in the operating system. I/O requests are issued by applications and device drivers and are scheduled by the OS. Data transfer techniques include programmed I/O, interrupt-driven I/O, and direct memory access (DMA). Blocking and non-blocking operations, synchronous and asynchronous models describe how the caller waits for completion.

Performance is influenced by latency, bandwidth, and contention. Techniques such as buffering, caching, and pipelining help smooth data flow. The OS often maintains a separate I/O subsystem and device drivers; IO virtualization and emulation can provide virtualized I/O resources in environments such as hypervisors.

In software, I/O is commonly expressed as streams and file operations, with APIs offering read, write, and seek operations. Common concepts include file descriptors, handles, pipes, and network sockets. The term I/O is also used in broader contexts, such as database input/output and inter-process communication.