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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.arch
Subject: Re: Paging
Message-ID: <7114@utzoo.UUCP>
Date: Thu, 11-Sep-86 14:03:56 EDT
Article-I.D.: utzoo.7114
Posted: Thu Sep 11 14:03:56 1986
Date-Received: Thu, 11-Sep-86 14:03:56 EDT
References: <8494@duke.duke.UUCP> <147@eneevax.UUCP>, <7621@tekecs.UUCP>
Organization: U of Toronto Zoology
Lines: 23

> I had always thought that virtual memory meant address translation only, and
> that a memory hierarchy (cache, RAM, disk, tape, ...) did not necessarily
> exist in a virtual memory system. When I looked it up, however, my textbooks
> speak of virtual memory as a way to map backing store into the address space
> of the processor...
> 
> I got two points from this reading. 1) Virtual memory *technically* implies
> only address translation, and 2) The main advantage to using virtual memory
> is to extend physical memory via a backing store (disk, drum, ...)...

Can you explain how you arrived at those points from the evidence presented?
Your textbooks clearly state that virtual memory IS the extension of physical
memory via a backing store.  They are correct; the phrase first came into
use to describe exactly that concept.  It's true that its literal meaning is
a bit different, but that's true of any idiomatic term.  The literal meaning
of "computer" is "something which computes, i.e. does arithmetic".  This then
includes a human with a slide rule (in fact, fifty years ago "computer" was
the job title for a desk-calculator operator) and probably does not include
a database machine (which does little or no arithmetic).  But that's not the
meaning normally understood for "computer".
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,decvax,pyramid}!utzoo!henry