Date:	Tue, 24 Mar 1998 17:00:24 +0300 (IDT)
From:	Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
To:	Shawn Hargreaves <ShawnH AT Probe DOT co DOT uk>
cc:	djgpp AT delorie DOT com
Subject:	RE: Allocate physical memory?
In-Reply-To:	<D1FB30BBA491D1118E6D006097BCAE391ABC06@Probe-nt-2a.Probe.co.uk>
Message-ID:	<Pine.SUN.3.91.980324165618.22871E-100000@is>
MIME-Version:	1.0

On Tue, 24 Mar 1998, Shawn Hargreaves wrote:

> Does anyone here have any experience of using these VDS functions?

Sorry, I don't have any first-hand experience with VDS.

> > Why do you think conventional memory won't work on Windows?
> 
> My understanding is that Windows may remap the conventional memory
> to any part of your physical RAM: otherwise how could it run 
> multiple DOS boxes at the same time? It works to program the DMA 
> controller directly with a conventional memory address, because
> Windows will recognise what you are trying to do and arrange for
> the memory to be remapped in a suitable way, but it has no way of
> knowing what is going on with the VBE/AF driver and graphics 
> controller.

But it might be that Windows does the same kind of magic with any VDS 
call as well, or for VBE/AF drivers, for that matter.

> but I'm pretty sure 
> that in Windows there is no 1 <-> 1 mapping between conventional 
> and physical memory...

This is correct.  However, Windows does a lot behind the scenes to create
the illusion that the mapping is 1:1.  Too many DOS programs assume that 
and would break otherwise.  I don't really know if VDS and VBE/AF are 
part of this magic, but there surely is no reason to believe they aren't.

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