peripheral

adj. of the circumference; circumferential; marginal; external, outer, exterior

n. auxiliary equipment that is connected to a computer (printer, keyboard, etc.)

For an account of the words periphery and peripheral as they are used in biology, sociology, politics, computer hardware, and other fields, see the periphery disambiguation page. A peripheral is a piece of computer hardware that is added to a host computer ,i.e any hardware except the computer, in order to expand its abilities. More specifically, the term is used to describe those devices that are optional in nature, as opposed to hardware that is either demanded or always required in principle.
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(a.)
Of or pertaining to a periphery; constituting a periphery; peripheric.
  

(a.)
External; away from the center; as, the peripheral portion of the nervous system.
  

<hardware> (Or "peripheral device", "device") Any part of a computer other than the CPU or working memory, i.e. disks, keyboards, monitors, mice, printers, scanners, tape drives, microphones, speakers, cameras, to list just the less exotic ones.
High speed working memory, such as RAM, ROM or, in the old days, core would not normally be referred to as peripherals. The more modern term "device" is also more general in that it is used for things such as a pseudo-tty, a RAM drive, or a network adaptor.
Some argue that, since the advent of the personal computer, the motherboard, hard disk, keyboard, mouse, and monitor are all parts of the base system, and only use the term "peripheral" for optional additional components.
(2002-09-03)

Noun
1. (computer science) electronic equipment connected by cable to the CPU of a computer; "disk drives and printers are important peripherals"
(synonym) computer peripheral, peripheral device
(hypernym) electronic equipment
(hyponym) printer
(part-holonym) computer, computing machine, computing device, data processor, electronic computer, information processing system
(classification) computer science, computing
Adjective
1. on or near an edge or constituting an outer boundary; the outer area; "Russia's peripheral provinces"; "peripheral suburbs"
(antonym) central
(similar) circumferential
2. related to the key issue but not of central importance; "a peripheral interest"; "energy is far from a peripheral issue in the economy"; "peripheral issues"
(similar) incidental, incident