A peripheral (pronounced peh-RIHF-uh-ruhl, a noun truncation of peripheral device, ) is any computer device that is not part of the essential computer (the processor, memory, and data paths) but is situated relatively close by.

A near synonym is input/output (I/O) device. Some peripherals are mounted in the same case with the main part of the computer as are the hard disk drive, CD-ROM drive, and NIC.

Other peripherals are outside the computer case, such as the printer and image scanner, attached by a wired or wireless connection.

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