peripheral : a device connected to a computer to provide communication (as input and output) — Webster
Peripheral is a device connected to a host computer, but not part of it, and is more or less dependent on the host. These are also input/output devices. It expands the host’s capabilities, but does not form part of the core computer architecture. An output peripheral is an external device that provides input and output for the computer. For example RAM has a peripheral output. Some peripherals, such as the external hardrive, provide both input and output for the computer. Usually for every external device there are input and output peripherals. An example of only input peripherals, a keyboard and a mouse are input and peripherals. An example of an output peripherals are hard drives disk. — Wikipedia
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