<communications> Used to describe a communications channel that can carry signals in both directions, in contrast to a simplex channel which only ever carries a signal in one direction.

If signals can only flow in one direction at a time the communications is "half-duplex", like a single-lane road with traffic lights at each end. Walkie-talkies with a "press-to-talk" button provide half-duplex communications.

If signals can flow in both directions simultaneously the communications is "full-duplex", like a normal two-lane road. Telephones provide full-duplex communications.

The term "duplex" was first used in wireless, telegraph, and telephone communications. Nearly all communications circuits used by computers are two-way, so the term is seldom used.


(01 Jun 2001)

Duplex escapement, a peculiar kind of watch escapement, in which the scape-wheel has two sets of teeth.

Duplex lathe, one for turning off, screwing, and surfacing, by means of two cutting tools, on opposite sides of the piece operated upon.

Duplex pumping engine, a steam pump in which two steam cylinders are placed side by side, one operating the valves of the other. Duplex querela; Latin; double complaint.

A complaint in the nature of an appeal from the ordinary to his immediate superior, as from a bishop to an archbishop. Duplex telegraphy, a system of telegraphy for sending two messages over the same wire simultaneously. Duplex watch, one with a duplex escapement.

Alternative forms: double, twofold.

Origin: L, fr. Duo two + plicare to fold.

(01 Mar 1998)