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 facsimile of the
original. A fax machine is made up of a scanner, printer and modem
with fax signaling.
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 resolution is 203x98 dpi in
standard mode, 203x196 in fine mode and 203x392 in super fine
mode.
Group 3 is still the standard today, 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
or Switched 56 circuits.
