The word "modem" is a contraction of the words
modulator-demodulator. A modem is typically used to send digital
data over a phone line. The sending modem modulates the data
into a signal that is compatible with the phone line, and
the receiving modem demodulates the signal back into digital
data. Wireless modems convert digital data into radio signals
and back.
Modems came into existence in the 1960s as a way to allow
terminals to connect to computers over the phone lines. The
1960s were the age of time-shared computers, so a business
would often buy computer time from a time-share facility and
connect to it via a 300-bit-per-second (bps) modem. In a system
configuration existed at that time, a dumb terminal at an
off-site office or store could "dial in" to a large,
central computer.
A dumb terminal is simply a keyboard and a screen. A very
common dumb terminal at the time was called the DEC VT-100,
and it became a standard of the day (now memorialized in terminal
emulators worldwide). The VT-100 could display 25 lines of
80 characters each. When the user typed a character on the
terminal, the modem sent the ASCII code for the character
to the computer. The computer then sent the character back
to the computer so it would appear on the screen.
When personal computers started appearing in the late 1970s,
bulletin board systems (BBS) became highly popular. A person
would set up a computer with a modem or two and some BBS software,
and other people would dial in to connect to the bulletin
board. The users would run terminal emulators on their computers
to emulate a dumb terminal.
People got along at 300 bps for quite a while. The reason
this speed was tolerable was because 300 bps represents about
30 characters per second, which is a lot more characters per
second than a person can type or read. Once people started
transferring large programs and images to and from bulletin
board systems, however, 300 bps became intolerable. Modem
speeds went through a series of steps at approximately two-year
intervals:
300 bps - 1960s through 1983 or so
1200 bps and 2400 bps - Gained popularity in 1984 and 1985
9600 bps - First appeared in late 1990 and early 1991
19.2 Kbps, 28.8 Kbps and 33.6 Kbps became the standard in
Mid 90’s. Mostly used was the 33.6 Kbps Modem.
56 Kbps - Became the standard in 1998.
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