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From: suhre@trwrb.UUCP
Newsgroups: comp.sources.d,misc.misc
Subject: Re: Lisp operators
Message-ID: <1619@trwrb.UUCP>
Date: Thu, 26-Feb-87 13:43:06 EST
Article-I.D.: trwrb.1619
Posted: Thu Feb 26 13:43:06 1987
Date-Received: Sun, 1-Mar-87 09:00:05 EST
References: <1277@beta.UUCP> <517@cod.UUCP> <1297@zeus.TEK.COM>
Reply-To: suhre@trwrb.UUCP (Maurice E. Suhre)
Organization: TRW EDS, Redondo Beach, CA
Lines: 22
Xref: utgpu comp.sources.d:372 misc.misc:617

In article <1297@zeus.TEK.COM> dant@tekla.tek.com (Dan Tilque) writes:
>
>Many years ago at school when I learned Lisp (I've never used it since) I
>learned that there are essentially two operators in the language.  These
>are "CAR" and "CDR".  ("CDR" *is* pronounced "could-er".)  The interesting
>thing about them is their origin.  It seems that on the machine where
>the language was developed (at Stanford, I think; don't know what machine)
>there were two registers: a Current Address Register (CAR) and a Current
>Decrement Register (CDR).
The IBM 7094 had a 36 bit word, which could contain two 15 bit fields.
One was the "address", the other the "decrement".  There were LXA (Load
Index in Address), SXA, LXD, and SXD instructions.  I thought the acronyms
were CAR = Contents of Address Register, CDR = Contents of Decrement
Register.

So, the names CAR and CDR were spawned by the hardware implementation,
but not required by it.

-- 
Maurice Suhre

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