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1 definition found
 for modem
From The Free On-line Dictionary of Computing (30 December 2018) :

      (Modulator/demodulator) An
     electronic device for converting between serial data
     (typically EIA-232) from a computer and an audio signal
     suitable for transmission over a telephone line connected to
     another modem.  In one scheme the audio signal is composed of
     silence (no data) or one of two frequencies representing zero
     and one.
     Modems are distinguished primarily by the maximum data rate
     they support.  Data rates can range from 75 bits per second up
     to 56000 and beyond.  Data from the user (i.e. flowing from
     the local terminal or computer via the modem to the telephone
     line) is sometimes at a lower rate than the other direction,
     on the assumption that the user cannot type more than a few
     characters per second.
     Various data compression and error correction algorithms
     are required to support the highest speeds.  Other optional
     features are auto-dial (auto-call) and auto-answer which
     allow the computer to initiate and accept calls without human
     intervention.  Most modern modems support a number of
     different protocols, and two modems, when first connected,
     will automatically negotiate to find a common protocol (this
     process may be audible through the modem or computer's
     loudspeakers).  Some modem protocols allow the two modems to
     renegotiate ("retrain") if the initial choice of data rate is
     too high and gives too many transmission errors.
     A modem may either be internal (connected to the computer's
     bus) or external ("stand-alone", connected to one of the
     computer's serial ports).  The actual speed of transmission
     in characters per second depends not just the modem-to-modem
     data rate, but also on the speed with which the processor can
     transfer data to and from the modem, the kind of compression
     used and whether the data is compressed by the processor or
     the modem, the amount of noise on the telephone line (which
     causes retransmissions), the serial character format
     (typically 8N1: one start bit, eight data bits, no
     parity, one stop bit).
     See also acoustic coupler, adaptive answering, baud
     barf, Bulletin Board System, Caller ID, SoftModem,
     U.S. Robotics, UUCP, whalesong.
     Usenet newsgroup: news:comp.dcom.modems.

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