Subject: Re: why is the cdr pronounced could-er?
From: (Rob Warnock)
Date: 1999/06/24
Newsgroups: comp.lang.scheme
Message-ID: <7ks7jn$>
Fernando <spamers@must.die> wrote:
| That seems natural to you? :-O  Ok...  I thought it had something to
| do with the word "could", that's why I asked. :-)

"CDR" is an acronym, not an abbreviation per se. It stands for
"Contents [of the] Decrement Register" (and, yes, CAR == Contents
[of the] Address Register). The Address and Decrement Registers
were elements of the IBM 7090/7094 machine architecture...

"CONS", on the other hand, *is* an abbreviation (of "constructor", IIRC).


p.s. And since the PDP-10 [which has many similarities to a 7094]
registers also has an "address" part and a "decrement" (well, sometimes
used as an "increment") part -- when viewed by the PUSH/POP/AOBJx/etc. set
of instructions, it was natural to pack two addresses into a single PDP-10
word and call that a CONS cell. So if "t0" contained the address of an
object known to be a cons, the PDP-10 instruction "HRRZ t0,(t0)" *was*
the CAR operation, and "HLRZ t0,(t0)" *was* CDR.

Except since HRRZ & HLRZ were the same speed, I think they decided
to do it the other way 'round, for some reason (I forget)...

Rob Warnock, 8L-855
Applied Networking
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