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

El Camino Bignum
 /el' k@?mee?noh big?nuhm/, n.

    The road mundanely called El Camino Real, running along San Francisco
    peninsula. It originally extended all the way down to Mexico City; many
    portions of the old road are still intact. Navigation on the San Francisco
    peninsula is usually done relative to El Camino Real, which defines 
    logical north and south even though it isn't really north-south in many
    places. El Camino Real runs right past Stanford University and so is
    familiar to hackers.

    The Spanish word ?real? (which has two syllables: /ray?ahl'/) means
    ?royal?; El Camino Real is ?the royal road?. In the FORTRAN language, a
    real quantity is a number typically precise to seven significant digits,
    and a double precision quantity is a larger floating-point number, precise
    to perhaps fourteen significant digits (other languages have similar real
    types).

    When a hacker from MIT visited Stanford in 1976, he remarked what a long
    road El Camino Real was. Making a pun on ?real?, he started calling it ?El
    Camino Double Precision? ? but when the hacker was told that the road was
    hundreds of miles long, he renamed it ?El Camino Bignum?, and that name has
    stuck. (See bignum.)

    [GLS has since let slip that the unnamed hacker in this story was in fact
    himself ?ESR]

    In the early 1990s, the synonym El Camino Virtual was been reported as an
    alternate at IBM and Amdahl sites in the Valley.

    Mathematically literate hackers in the Valley have also been heard to refer
    to some major cross-street intersecting El Camino Real as ?El Camino
    Imaginary?. One popular theory is that the intersection is located near
    Moffett Field ? where they keep all those complex planes.


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

El Camino Bignum

    /el' k*-mee'noh big'nuhm/ The road mundanely called
   El Camino Real, a road through the San Francisco peninsula
   that originally extended all the way down to Mexico City and
   many portions of which are still intact.  Navigation on the
   San Francisco peninsula is usually done relative to El Camino
   Real, which defines logical north and south even though it
   isn't really north-south many places.  El Camino Real runs
   right past Stanford University.

   The Spanish word "real" (which has two syllables: /ray-al'/)
   means "royal"; El Camino Real is "the royal road".  In the
   Fortran language, a "real" quantity is a number typically
   precise to seven significant digits, and a "double
   precision" quantity is a larger floating-point number,
   precise to perhaps fourteen significant digits (other
   languages have similar "real" types).

   When a hacker from MIT visited Stanford in 1976, he
   remarked what a long road El Camino Real was.  Making a pun on
   "real", he started calling it "El Camino Double Precision" -
   but when the hacker was told that the road was hundreds of
   miles long, he renamed it "El Camino Bignum", and that name
   has stuck.  (See bignum).

   [Jargon File]

   (1996-07-16)