A Computer Modem
(which stands for modulator-demodulator) is a device that encodes digital information
over an analog signal (such as a phone line or radio), and also decodes the
analog signal to recover the digital information. The most familiar example
is a typical computer (voiceband) modem that turns the digital '1s and 0s' of
a personal computer into sounds that can be transmitted over the telephone lines.
You can have one PC Modem that sends and receives information from the Internet,
or a pair of modems can communicate via the phone line to form a closed network.
Modems are generally classified by the amount of data they can send in a given
time, normally measured in bits per second, or "bps". They can also
be classified by Baud, the number of distinct symbols transmitted per second.
Typically, the fastest modem that can be used over regular phone lines is a
56k baud modem.
Fewer users now use regular dial-up connections, so the need for slower modems
is far less. However, faster PC modems are used by Internet users every day,
such as: cable modems
and DSL modems (ADSL modems). In other forms of telecommunications, "radio
modems" transmit repeating frames of data at very high data rates over
microwave radio links. Some microwave modems transmit more than a hundred million
bits per second. Optical modems transmit data over optical fibers. Most intercontinental
data links now use optical modems transmitting over undersea optical fibers.
Optical modems routinely have data rates in excess of a billion (1x109) bits
per second.
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