Peripheral

A peripheral is a device attached to a computer to pass data in and out of the computer - either to secondary storage which is permanently accessible; some other form of data storage, intended for off-line storage; communication, either to users or other computers, etc.

Devices may use either programmed I/O or DMA to get data in and out of the CPU and/or main memory, and interrupts to get the CPU to pay attention to the device.