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.