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From: roy@phri.UUCP
Newsgroups: comp.arch
Subject: Re: 64 Vs 32
Message-ID: <2610@phri.UUCP>
Date: Sun, 22-Mar-87 11:53:15 EST
Article-I.D.: phri.2610
Posted: Sun Mar 22 11:53:15 1987
Date-Received: Wed, 25-Mar-87 01:09:17 EST
References: <3810013@nucsrl.UUCP> <985@rpics.RPI.EDU>
Reply-To: roy@phri.UUCP (Roy Smith)
Organization: Public Health Research Inst. (NY, NY)
Lines: 20
Summary: pdp-11 style memory mapping on vaxen?

In article <985@rpics.RPI.EDU> yerazuws@rpics.RPI.EDU (Crah) 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.

	Remember when the 11/45 came out and they managed to wedge an
18-bit physical address space onto a 16-bit machine and then the 11/70 came
along and they managed to extend that to 22 bits?  Anybody willing to guess
when we'll see 48 bit physical addresses on 32 bit machines?  Anybody for
demand paging and bank switching at the same time?

	A question: I remember reading somewhere that the top 2 bits in a
VAX address signify user/kernel and data/text segments, which really leaves
you with "only" a 30-bit address space.  Is that a hardware feature or just
the way VMS sets up the memory map?
-- 
Roy Smith, {allegra,cmcl2,philabs}!phri!roy
System Administrator, Public Health Research Institute
455 First Avenue, New York, NY 10016

"you can't spell deoxyribonucleic without unix!"