Path: utzoo!attcan!uunet!husc6!mailrus!ames!pasteur!agate!saturn!ucscc.UCSC.EDU!haynes
From: haynes@ucscc.UCSC.EDU (99700000)
Newsgroups: comp.os.misc
Subject: Re: Defining virtual memory (was: a very naive Question???)
Message-ID: <5133@saturn.ucsc.edu>
Date: 15 Oct 88 06:08:00 GMT
References: <835@amethyst.ma.arizona.edu> <5085@medusa.cs.purdue.edu> <664@cme-durer.ARPA> <5102@medusa.cs.purdue.edu> <73039@sun.uucp>
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Reply-To: haynes@ucscc.UCSC.EDU (Jim Haynes)
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In article <73039@sun.uucp> rfm@sun.UUCP (Rich McAllister) writes:
>Also, the common definition of virtual is "existing in appearance but not 
>in fact," which doesn't seem to apply to a simple remapping of addresses
>of memory which exists "in fact".
Wellll - maybe so, maybe not.  Maybe it's not the storage itself that
"exists in appearance but not in fact" but rather some other attribute
of memory, such as how it is addressed.  For instance, let's consider
the old base-address-and-boundary register scheme such as the GE635
and its descendants employed.  Now here all the memory the user program
sees is really there; but the virtual addresses, those used by the
user program, are in a space that begins at address zero.  But only
the entire virtual space can reside either in main memory or not
in main memory when it's swapped out.  There is no provision for
part of the space to be resident and part non-resident.  Yet I would
say that this memory is in some sense virtual.
>
>A proper definition of "virtual memory" should capture the idea that the
>data stored in a part of the address space may be held somewhere other
>than in main storage when not being referenced.  
>
>
>Rich McAllister (rfm@sun.com)

Well, then, we need some other term to use for the larger class of
schemes in which addresses in programs are mapped before being used
to address physical memory.
haynes@ucscc.ucsc.edu
haynes@ucscc.bitnet
..ucbvax!ucscc!haynes

"Any clod can have the facts, but having opinions is an Art."
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