Any peripheral gadget that links to a computer for input or output is an auxiliary. When a device is attached, it can do so electronically or directly and is managed by the computer. Accessories or merely "I/O devices" are other names for peripherals.

Depending on whether they deliver input, receive output, or both, peripherals can be categorized. A keypad and mouse are two examples of entry devices that transmit human instructions to a computer. An output device, such as a monitor, transfers data from the computer and shows it on the screen. When writing, a multi-function printer offers both input and output (when scanning). In the shape of data going back and forth between it and the computer, an auxiliary storage device similar to a flash drive also offers input and output.

Hardware interfaces are used by peripherals to directly attach to a computer. Although Thunderbolt, HDMI, Display Port, and audio interfaces are also widely used, USB is the most common link. Although some devices interact by RF through an adapter that is directly connected to a computer, Bluetooth is still the most popular type of wireless communication. Most devices are plug-and-play, but some require a program driver in order for the computer to communicate with it.