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electrical device having two states: on, or closed; and off, or open. Ideally a switch offers a zero impedanceimpedance,
in electricity, measure in ohms of the degree to which an electric circuit resists the flow of electric current when a voltage is impressed across its terminals.
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 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 transistorstransistor,
three-terminal, solid-state electronic device used for amplification and switching. It is the solid-state analog to the triode electron tube; the transistor has replaced the electron tube for virtually all common applications.
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 are used instead. The PIN diodediode
, two-terminal electronic device that permits current flow predominantly in only one direction. Most diodes are semiconductor devices; diode electron tubes are now used only for a few specialized applications.
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, 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 relayrelay,
electromechanical switch operated by a flow of electricity in one circuit and controlling the flow of electricity in another circuit. A relay consists basically of an electromagnet with a soft iron bar, called an armature, held close to it.
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See J. C. McDonald, Fundamentals of Digital Switching (1990).

The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/


In electrical work, a device for closing, opening, or changing the connections of the circuit in which it is placed.
Illustrated Dictionary of Architecture Copyright © 2012, 2002, 1998 by The McGraw-Hill Companies, Inc. All rights reserved
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



a device that selects the required output circuit (or circuits) and connects to it an input circuit (or circuits) by means of connection, disconnection, or commutation. The selection may be manual or automatic, following a program stated in terms of a time or state function of other electric circuits. Switches are a component of more complex data-transmission equipment used in telemechanics and communications engineering, and they are used to solve programming and control problems in computer technology and to connect circuits in electric machines.

A distinction is made among electromechanical, electronic, and electron-beam switches. The simplest electromechanical switches are knife switches, commutators of electric machines, and sets of electromagnetic relays or electromechanical selectors. More complex switches are electronic devices assembled according to definite functional schemes; they may include ionic devices, electron tubes, semiconductor devices, and electron-tube commutators, as well as gas-discharge tubes and circulators (for ultrahigh frequencies).

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


(computer science)
A hardware or programmed device for indicating that one of several alternative states or conditions have been chosen, or to interchange or exchange two data items.
A symbol used to indicate a branch point, or a set of instructions to condition a branch.
(civil engineering)
A device for enabling a railway car to pass from one track to another.
The junction of two tracks.
A manual or mechanically actuated device for making, breaking, or changing the connections in an electric circuit. Also known as electric switch. Symbolized SW.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


A device used to open or close an electric circuit or to change the connection of a circuit.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.


1. a mechanical, electrical, electronic, or optical device for opening or closing a circuit or for diverting energy from one part of a circuit to another
2. the tassel-like tip of the tail of cattle and certain other animals
3. any of various card games in which the suit is changed during play
4. US and Canadian a railway siding
5. US and Canadian a railway point
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005






This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)


(1) A network cross connect. See Ethernet switch.

(2) In programming, a bit or byte used to keep track of some event. The term is sometimes synonymous with the branch command.

(3) In programming, a statement that saves the programmer from having to write multiple compare statements. See event loop.

(4) A modifier of a command. For example, in the Windows/DOS command dir /p the /p is a switch that modifies the Dir command to pause after each screenful. See Dir.

(5) A mechanism that allows each key to be depressed on a keyboard. See mechanical keyboard.

(6) A mechanical or electronic device that directs the flow of electrical or optical signals from one side to the other. Switches with more than two ports, such as a LAN switch or PBX, are able to route traffic. See transistor, Ethernet switch, softswitch, PBX and data switch.

With regard to a simple on/off switch, remember... Open is "off." Closed is "on."

Mechanical and Semiconductor Switches
The semiconductor transistor performs the same function as a light switch on the wall. The switch is electronically closed by sending a pulse to the trigger. See transistor.

A Manual Switch
This early switch panel from New York Electric Switchboard Company was used to manually open and close electric lines.
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