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Date: Sun, 25 Feb 2024 21:58:39 +0200
Message-Id: <86a5nowc28.fsf@gnu.org>
From: "Eli Zaretskii (eliz AT gnu DOT org) [via djgpp AT delorie DOT com]" <djgpp AT delorie DOT com>
To: djgpp AT delorie DOT com
In-Reply-To:
	<CALPW7mSqDTJcOs0JywP8Q8OPQHsj-qVR8dQsAyCkZUo2OPo_kw AT mail DOT gmail DOT com>
	(djgpp AT delorie DOT com)
Subject: Re: DJGPP documentation updates
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Reply-To: djgpp AT delorie DOT com

> From: "A. Wik (awik32 AT gmail DOT com) [via djgpp AT delorie DOT com]" <djgpp AT delorie DOT com>
> Date: Sun, 25 Feb 2024 19:28:07 +0000
> 
> On Sun, 25 Feb 2024 at 17:11, Eli Zaretskii (eliz AT gnu DOT org) [via
> djgpp AT delorie DOT com] <djgpp AT delorie DOT com> wrote:
> >
> > > I'm not sure now if I understood it correctly. But my understanding of
> > > the spec is that DPMI host which supports paging may page-out also
> > > linear addresses below 1 MB.
> >
> > Really?  IME, no DPMI host does that.  DOS memory is always mapped
> > 1:1, AFAIR.
> 
> Windows maps VMs one at a time into the low 1 MB, although the memory
> that was in use when Windows started is replicated (at the same linear
> address) in all the VMs.  A VM is approximately a "DOS box", but there
> is always a so-called "system" VM in which (usually) the GUI is
> running.
> 
> There is also expanded memory (LIM EMS) that involves mapping the
> "expanded" memory into or out of a program's low 1 MB address space.

I think there's a misunderstanding here.  The issue at hand is whether
the DOS memory's linear address, as it appears within a certain VM,
can ever have the value above 1MB.  If the linear address is _always_
below 1MB, then for all practical purposes it is the same as the
"physical address", since what the VM does under the hood is none of
the business of the DJGPP programmer.