Source : Free On-Line Dictionary of Computing

TMRC
     
        /tmerk'/ The Tech Model Railroad Club at {MIT}, one of the
        wellsprings of {hacker} culture.  The 1959 "Dictionary of the
        TMRC Language" compiled by Peter Samson included several terms
        that became basics of the hackish vocabulary (see especially
        {foo}, {mung}, and {frob}).
     
        By 1962, TMRC's legendary layout was already a marvel of
        complexity (and has grown in the thirty years since; all the
        features described here are still present).  The control
        system alone featured about 1200 relays.  There were {scram
        switch}es located at numerous places around the room that
        could be thwacked if something undesirable was about to occur,
        such as a train going full-bore at an obstruction.  Another
        feature of the system was a digital clock on the dispatch
        board, which was itself something of a wonder in those bygone
        days before cheap LEDS and seven-segment displays.  When
        someone hit a scram switch the clock stopped and the display
        was replaced with the word "FOO"; at TMRC the scram switches
        are therefore called "foo switches".
     
        Steven Levy, in his book "Hackers", gives a stimulating
        account of those early years.  TMRC's Power and Signals group
        included most of the early {PDP-1} hackers and the people who
        later bacame the core of the {MIT} {AI Lab} staff.  Thirty
        years later that connection is still very much alive, and this
        dictionary accordingly includes a number of entries from a
        recent revision of the TMRC dictionary (via the Hacker Jargon
        File).
     
        [{Jargon File}]