Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!mit-eddie!uw-beaver!tektronix!orca!tekecs!frip!andrew
From: andrew@frip.gwd.tek.com (Andrew Klossner)
Newsgroups: comp.os.cpm
Subject: Re: a very naive Question???
Message-ID: <10460@tekecs.TEK.COM>
Date: 12 Oct 88 14:38:19 GMT
References: <836@amethyst.ma.arizona.edu>
Sender: news@tekecs.TEK.COM
Organization: Tektronix, Wilsonville, Oregon
Lines: 35

Lots of errors and inconsistencies in this discussion, mostly based on
terminology disagreement.

	"I read an article in UNIX World comparing system V and AIX. It
	clearly stated that System V did not have VM(Virtual Memory
	concept)."

As has been pointed out, the initials "VM" in the IBM mainframe world
stand for "virtual machine," a completely different animal from
"virtual memory."

		"The actual definition of Virtual Memory involves the
		concept of allowing programs to believe that they are
		running at a particular address, when in fact they may
		actually be at a completely different *physical*
		address."

	"Wrong. The actual concept of virtual memory is the ability to
	allow programs to use more memory than the machine physically
	has by swapping the least recently used pages to secondary
	storage."

The term "virtual memory" has different definitions depending on who
you talk to and when you talk to them.  You can find texts that define
VM in both of the above ways.  The original poster was not "wrong."

	"Demand paging involves only the code portion of the program."

I've never heard this before.  In my (not trivial) experience, the term
"demand paging" always refers to dynamic paging of both instructions
and data.  I'd be interested in references to articles or books that
employ this restricted definition.

  -=- Andrew Klossner   (uunet!tektronix!tekecs!frip!andrew)    [UUCP]
                        (andrew%frip.gwd.tek.com@relay.cs.net)  [ARPA]