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From: peter@sugar.UUCP (Peter da Silva)
Newsgroups: comp.sys.amiga
Subject: Re: Argument for Virtual Memory
Message-ID: <1122@sugar.UUCP>
Date: Fri, 27-Nov-87 11:30:46 EST
Article-I.D.: sugar.1122
Posted: Fri Nov 27 11:30:46 1987
Date-Received: Sun, 29-Nov-87 23:54:37 EST
References: <8711151944.AA25448@cory.Berkeley.EDU> <1089@sugar.UUCP> <1912@ncr-sd.SanDiego.NCR.COM>
Organization: Sugar Land UNIX - Houston, TX
Lines: 47
Summary: Virtual definitions.

Me:
>Virtual memory is what you have when part of the memory a program uses isn't
>in real RAM, but is copied in from secondary storage on demand. This usually
>requires memory management.

In article <1912@ncr-sd>, greg@ncr-sd.SanDiego.NCR.COM (Greg Noel) writes:
> This is a definition for "swapping," and not for virtual memory, although the
> two are frequently found in the same system.

Please, let's not have the "virtual definitions wars" here. We just got done
with them elsewhere on the net.

Program may be moved in memory without knowing about it.

	Some people call this virtual memory, some people call this mapped
	or managed memory. Depends on whether your school used IBM, DEC,
	CDC, or whatever other equipment.

Program may be copied entirely to disk and then back into memory.

	I call this swapping.

Program may be partially copied to disk and reloaded on demand: when the
program needs that code or data.

	Some people call this virtual memory. The people who call what I
	call mapped memory vitual memory call this demand paged virtual memory.

The point of my article remains: to wit...

	a) Mapped memory,
	b) Protected memory,
	c) Demand Paged Virtual Memory,

May be mixed and matched. You can have any combination of these any
way you like, and there have been implementations of same.

	a only: Minix has this.
	b only: Amiga has this (WCS RAM).
	c only: this appears to be what C= has in mind for VMAmiga.
	a+b: Most '70s 16-bit minis did this.
	a+c: FORTH's disk management uses a technique like this.
	b+c: This one I don't know about. C= may be thinking of this.
	a+b+c: "Classical" VM system, such as the Vax.
-- 
-- Peter da Silva  `-_-'  ...!hoptoad!academ!uhnix1!sugar!peter
-- Disclaimer: These U aren't mere opinions... these are *values*.