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From: tuba@ur-tut.UUCP (Jon Krueger)
Newsgroups: comp.arch
Subject: Re: 64 Vs 32
Message-ID: <1092@ur-tut.UUCP>
Date: Sun, 15-Mar-87 20:51:44 EST
Article-I.D.: ur-tut.1092
Posted: Sun Mar 15 20:51:44 1987
Date-Received: Mon, 16-Mar-87 04:46:13 EST
References: <3810013@nucsrl.UUCP> <985@rpics.RPI.EDU>
Reply-To: tuba@tut.cc.rochester.edu.UUCP (Jon Krueger)
Organization: Univ. of Rochester Computing Center
Lines: 18


Bill Yerazunis "VAXstation Repo Man" writes:
> A VAX has 32 bits- so if we assume (*) that all 32
>can be used as memory address, a VAX (or other 32-bit processor)
>can have AT MOST 4 GIG of memory.
>   (*) assumptions like this are never valid.

VAX architecture limits each process to a virtual 32 bit space.  The
processor may generate physical addresses of different sizes.  VAX
implementations have supported physical spaces as small as 24 bits
(microvax) and as large as 30 bits (11/780).  Therefore, DEC could
choose to do with VAX as they did with PDP-11s, support virtual spaces
smaller than available physical memory.  Of course, that might not
be the Thing To Do, for a variety of reasons.

-- 
Jon Krueger   Department of Necessary Evil   University of Rochester
uucp: {seismo, allegra, decvax}!rochester!ur-tut!tuba   BITNET: TUBA@UORDBV