The Jargon File (version 4.4.7, 29 Dec 2003):

TMRC
 /tmerk'/, n.

    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
    esp. foo, mung, and frob).

    By 1962, TMRC's legendary layout was already a marvel of complexity and has
    grown in the years since. All the features described here were still
    present when the old layout was decommissioned in 1998 just before the
    demolition of MIT Building 20, and will almost certainly be retained when
    the old layout is rebuilt (expected in 2003). The control system alone
    featured about 1200 relays. There were scram switches 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 (see the Bibliography in Appendix C),
    gives a stimulating account of those early years. TMRC's Signals and Power
    Committee included many of the early PDP-1 hackers and the people who later
    became the core of the MIT AI Lab staff. Thirty years later that connection
    is still very much alive, and this lexicon accordingly includes a number of
    entries from a recent revision of the TMRC dictionary.

    TMRC has a web page at http://tmrc-www.mit.edu/. The TMRC Dictionary is
    available there, at http://tmrc-www.mit.edu/dictionary.html.


The Free On-line Dictionary of Computing (30 December 2018):

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
   switches 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.  This
   dictionary accordingly includes a number of entries from the
   TMRC dictionary (via the Hacker Jargon File).

   [Jargon File]

   (2008-06-30)