fax

fax: see facsimile.

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fax

 in full facsimile

Device for the transmission and reproduction of documents by digitized signals sent over telephone lines. Fax machines scan printed text and graphics and convert the image into a digital code: 1 for dark areas, 0 for white areas. The code is transmitted through the telephone network to similar devices, where the documents are reproduced in close to their original form. Though the concepts for fax technology were developed in the 19th century, widespread use did not occur until the 1970s, when inexpensive means of adapting digitized information to telephone circuits became common.

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(FACSimile) Originally called "telecopying," it is the communication of a printed page between remote locations. Fax machines scan a paper form and transmit a coded image over the telephone system. The receiving machine prints a copy (a facsimile) of the original. A fax machine is made up of a scanner, printer and modem with fax signaling.

Group 1, 2, 3 and 4
Fax standards were developed starting in 1968 and are classified by Groups. Groups 1 and 2, used until the late 1980s, transmitted a page in six and three minutes respectively. Group 3 transmits at less than one minute per page and uses data compression at 9,600 bps. The Group 3 speed increase led to the extraordinary rise in usage in the late 1980s. Group 3 resolutions are 203x98 dpi in standard mode, 203x196 in fine mode and 203x392 in super fine mode.

Group 3 is the common standard, but Group 4 machines can transmit a page in just a few seconds and provide up to 400x400 resolution. Group 4 requires 56 to 64 Kbps bandwidth and needs ISDN, Switched 56 circuits or DSL lines. See fax/modem and e-mail.

A Different Kind of Fax Machine

This earlier portable fax machine from Reflection Technology weighed eight ounces, worked with most cellphones and stored 25 fax pages. Its virtual display simulated a 12" monitor, and its "virtual keyboard" (lever and buttons on top) let you select menu options. (Image courtesy of Reflection Technology, Inc.)

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fax - facsimile