Input/output

In computing, input/output (I/O, i/o, or informally io or IO) is how a computer connects with the world outside it. This includes other computers, devices like printers, or even people. Inputs are the information the computer receives. Outputs are the information the computer sends out.

I/O devices are tools that help people and computers talk to each other. For example, a keyboard or computer mouse is an input device because they let you give information to the computer. On the other hand, things like monitors and printers are output devices because they show or print what the computer decides to show. Some devices, like modems and network cards, can do both — they can send information out and receive it back.

The way we see if a device is input or output can change depending on who you ask. For a user, typing on a keyboard is an output because you’re sending information out, but for the computer, that typing is an input because it’s receiving the information. This back-and-forth is an important part of how computers and people work together, a field known as human–computer interaction.

Inside the computer, the CPU and main memory are like the brain. Any time information moves in or out of this brain — like when you load a file from a disk drive — that’s I/O. Computers have special ways to handle this, like memory-mapped I/O, which helps them manage tasks like talking to devices through device drivers or using I/O channels. All of this makes sure that computers can efficiently move data, whether it’s saving a picture or loading a game.

Interface

An I/O interface helps a computer talk to devices like keyboards or printers. It uses special signals so the computer knows when a device is ready to send or receive information. This way, the computer doesn’t waste time waiting.

Computers can handle inputs and outputs in different ways. Some use special memory spots to talk to devices, while others need unique commands. Programs and operating systems each have their own ways to manage inputs and outputs. This makes it easier for software to work with hardware.

Channel I/O

Channel I/O uses special instructions to manage input and output tasks. These instructions speak to the channel or both the channel and the device. The channel then takes care of all the details needed to control and send the information. It works on its own, separate from the main system. This method is similar to direct memory access (DMA) but offers more flexibility.

Main article: Channel I/O

Port-mapped I/O

Port-mapped I/O uses special commands to talk to devices. Each device gets one or more ports. Each port has a special job. These port numbers are stored in a special place, apart from the usual memory addresses used by the computer's normal commands.

Direct memory access

Direct memory access (DMA) is a way for devices to move lots of data to and from memory. It does this without always needing help from the computer's main processor. This makes moving data faster and more efficient.