Email from Steve Russell

from: http://www.iwriteiam.nl/HaCAR_CDR.html

I wrote the first implemenation of a LISP interpreter on the IBM 704 at MIT in early in 1959. I hand-compiled John McCarthy's "Universal LISP Function".

The 704 family (704, 709, 7090) had "Address" and "Decrement" fields that were 15 bits long in some of the looping instructions. There were also special load and store instructions that moved these 15-bit addresses between memory and the index regiseters ( 3 on the 704, 7 on the others )

We had devised a representation for list structure that took advantage of these instructions.

Because of an unfortunate temporary lapse of inspiration, we couldn't think of any other names for the 2 pointers in a list node than "address" and "decrement", so we called the functions CAR for "Contents of Address of Register" and CDR for "Contents of Decrement of Register".

After several months and giving a few classes in LISP, we realized that "first" and "rest" were better names, and we (John McCarthy, I and some of the rest of the AI Project) tried to get people to use them instead.

Alas, it was too late! We couldn't make it stick at all. So we have CAR and CDR.