[W/K] :: modem

  modulator-demodulator \mod"u*la`tor-de`mod"u*la`tor\, n.
     An electronic device that converts electronic signals into
     sound waves, and sound waves into electronic signals, used to
     transmit information between computers by the use of ordinary
     telephone lines; usually called a modem.
     [PJC]

  modem \mo"dem\ (m[=o]"d[e^]m), n. [by shortening from
     modulator-demodulator.]
     An electronic device that converts electronic signals into
     sound waves, and sound waves into electronic signals, used to
     transmit information between computers by the use of ordinary
     telephone lines; also called modulator-demodulator; as, the
     latest modems can transmit data at 56,000 baud over a clear
     telephone line. The speed of transmission of information by a
     modem is usually measured in units of baud, equivalent to
     bits per second.
     [PJC]

  modem
       n : (from a combination of MOdulate and DEModulate) electronic
           equipment consisting of a device used to connect
           computers by a telephone line

  MODEM
       MOdulator DEModulator
       
       

  modem
       
           (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.
       
          (2002-05-04)