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From: daveb@geac.UUCP (Brown)
Newsgroups: comp.arch
Subject: Re: *Why* do modern machines mostly hav
Message-ID: <1155@geac.UUCP>
Date: Mon, 17-Aug-87 08:06:03 EDT
Article-I.D.: geac.1155
Posted: Mon Aug 17 08:06:03 1987
Date-Received: Tue, 18-Aug-87 01:43:09 EDT
References: <2807@phri.UUCP> <101200004@datacube> <1332@killer.UUCP> <8974@beta.UUCP> <25740@sun.uucp>
Reply-To: daveb@geac.UUCP (Dave Collier-Brown)
Organization: The little blue rock next to that twinkly star.
Lines: 19

In article <25740@sun.uucp> guy%gorodish@Sun.COM (Guy Harris) writes:
>> This is also the classic C example of a normal (int, float, etc) pointer
>> at 18-bits being shorter than a 'char *' at 36 bits.
>In other words, an array of 10 "int *"s would require 5 words, not 10, and an
>"int **" would require at least 19 bits...
> ...  I'd be surprised if this was the case in any DEC-10 or
>DEC-20 C implementation. 

I'm not sure about the DEC-10, but the Honeywell 36-bit machines used
the high half (the CAR) of the word as a pointer-to-word, and any
bit/byte addressing info was in the high end of the lower half.  The
C (and late-model B!) compilers therefore had an addressing scheme
that was guaranteed to fit in whole-words, even if the pointers were
to bits... :-).
-- 
 David Collier-Brown.                 |  Computer Science
 Geac Computers International Inc.,   |  loses its memory
 350 Steelcase Road,Markham, Ontario, |  (if not its mind)
 CANADA, L3R 1B3 (416) 475-0525 x3279 |  every 6 months.