switch

switch electrical device having two states: on, or closed; and off, or open. Ideally a switch offers a zero impedance to a current when it is closed, and it offers infinite impedance when open. Mechanical switches, which operate by moving contacts together and apart, are often classified by the number of connections they can make or break at once and the number of closed positions in which they can be placed. A single-pole double-throw switch can be placed in either of two closed positions, making one connection in each position. A double-pole single-throw switch can open or close two connections at once. For many operations, as in computers and digital telecommunications, the operation of mechanical switches is too slow and transistors are used instead. The PIN diode , which contains an intermediate intrinsic layer between the n -type and p -type layers, is also used as a simple switch. This device, which normally acts as a conductor, acts as a strong dielectric when the intrinsic layer is reverse biased. See relay .

Bibliography: See J. C. McDonald, Fundamentals of Digital Switching (1990).

switching Any of various communication techniques that provide point to point transmission between dynamically changing data sources and sinks. See also packet switching, message switching, circuit switching.

switch / swich/ • n. 1. a device for making and breaking the connection in an electric circuit: the guard hit a switch and the gate swung open. ∎  Comput. a program variable that activates or deactivates a certain function of a program. 2. an act of adopting one policy or way of life, or choosing one type of item, in place of another; a change, esp. a radical one: his friends were surprised at his switch from newspaper owner to farmer. 3. a slender flexible shoot cut from a tree. 4. a junction of two railroad tracks, with a pair of linked tapering rails that can be moved laterally to allow a train to pass from one line to the other. 5. a tress of false or detached hair tied at one end, used in hairdressing to supplement natural hair. • v. [tr.] 1. change the position, direction, or focus of: the company switched the boats to other routes. ∎  adopt (something different) in place of something else; change: she's managed to switch careers. ∎  [intr.] adopt a new policy, position, way of life, etc.: she worked as a librarian and then switched to journalism. ∎  substitute (two items) for each other; exchange: after ten minutes, listener and speaker switch roles. 2. archaic beat or flick with or as if with a switch. PHRASAL VERBS: switch something off turn off an electrical device. ∎  (switch off) inf. cease to pay attention: as he waffles on, I switch off. switch something on turn on an electrical device.DERIVATIVES: switch·a·ble adj.