On a photocopier or computer printer, duplex refers to the ability to print on both sides of each piece of paper. Most often, this is done by printing one side, shunting the paper into a special tray or duplexer unit, shunting it back in such a way that the other side is up, then printing the other side.

Because the addition of a duplexer increases the complexity of the printer's paper path, it slightly increases the chance of a paper jam. However, printing in duplex cuts in half the amount of paper you need to print your documents. Save a tree -- print in duplex.


A duplex can also be a house made of exactly two apartments. The apartments in a duplex are frequently substantially identical; sometimes they are mirror images of one another.

In data communications, duplex refers to whether the communication can happen in only one direction at a time, or in both directions at once. Half-duplex means communication can only occur in one direction at at time, like a CB radio; full-duplex means communications can occur in both directions at once, like a telephone. Old modems used to have a mechanical switch to specify half- or full-duplex, so a common cry over a telephone line when attempting to get a data call going was "Check your duplex switch!"

Du"plex (?), a. [L., fr. duo two + plicare to fold. See Two, and Complex.]

Double; twofold.

Duplex escapement, a peculiar kind of watch escapement, in which the scape-wheel has two sets of teeth. See Escapement. --
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 [L., double complaint] (Eccl. Law), a complaint in the nature of an appeal from the ordinary to his immediate superior, as from a bishop to an archbishop. Mozley & W. --
Duplex telegraphy, a system of telegraphy for sending two messages over the same wire simultaneously. --
Duplex watch, one with a duplex escapement.

 

© Webster 1913


Du"plex (?), v. t. [See Duplex, a.] (Teleg.)

To arrange, as a telegraph line, so that two messages may be transmitted simultaneously; to equip with a duplex telegraphic outfit.

 

© Webster 1913

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