LISP implementations on small machines

From: Mark Kahrs Sent: Tuesday, October 01, 2019 7:24 PM In the 70x series of IBM scientific systems (704, 709, 7040, 7090, 7044, 7094), the word "register" referred to memory locations rather than to the accumulator or multiplier/quotient. Each memory register was 36 bits long, and could be treated as 4 fields: A 15 bit address, a 15 bit decrement, a 3 bit tag, and a 3 bit index selector. In the earliest implementation of LISP, there were 4 functions which returned the different parts of a register: CAR, CDR, CTR, and CIR. These were abbreviations for "Contents of the {Address, Decrement, Tag, Index} PART OF THE Register", not "Contents of the {Address, Decrement} Register" as is so often misstated. Rich NB: Information from a talk given on the history of Lisp by Herbert Stoyan at the 1984 ACM Conference on Lisp and Functional Programming Languages, and later verified by personal inspection of the code.