From:	Vinzent Hoefler <JeLlyFish DOT software AT gmx DOT net>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: DMA use in a Windows Dos Box (pls help)
Date:	Wed, 26 Jun 2002 21:02:52 +0200
Organization:	JeLlyFish software
References:	<226f48f21bb08b3688f34385ce536c18 DOT 34818 AT mygate DOT mailgate DOT org>
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To:	djgpp AT delorie DOT com
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"Simone Navari" <simnav AT email DOT it> wrote:

>To do it I use XMS services to allocate
>and lock memory but if I try to do it in a Windows Dos Box, the
>operating system halts my software when it calls the XMS lock service.
>Why Windows don't allow me to do this operation ?

Because Windows handles the memory in a virtual (paging) way, it can't
give you a physical address for such a block (it simply does not
exist), what the plain XMS-service normally does. This would mean, it
could not throw out the locked block to the paging file if physical
RAM is needed in another task, the block had to be a complete
contiguous section (not good for paging) and in such a way it would be
easily possible to knock down Windows by using all available memory
from within a DOS-session without any dirty tricks...


Vinzent.

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