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Mail Archives: djgpp/1997/06/06/09:20:26

From: "Charles Sandmann" <sandmann AT clio DOT rice DOT edu>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: DPMI Host limited to 64MB physical memory on Compaq PC ??
Date: Thu, 5 Jun 1997 13:54:23
Organization: Aspen Technology, Inc.
Lines: 27
Message-ID: <3396c50f.sandmann@clio.rice.edu>
References: <3396CF50 AT smtpgate DOT villingen>
Reply-To: sandmann AT clio DOT rice DOT edu
NNTP-Posting-Host: spica.dmccorp.com
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

> ( blank config.sys ), and loaded nothing in the autoexec.bat
> The dpmi info call reports 3840 physical pages ( = 15360 kBytes )

In this configuration, CWSDPMI uses the BIOS int 15h call to determine
how much memory is installed.  It seems your BIOS only reports 16Mb memory.
The maximum it can report via the BIOS call is 64Mb (since the return call
gives size in Kb in a single 16-bit register).

> With HIMEM.SYS /EISA loaded I get 62MB

This is interesting, since none of the HIMEM.SYS versions I have support
a /EISA switch.  I suspect this is an OEM enhancement to work around the
BIOS limitation.  I got some information about a XMS extension which allows
more than 64Mb to be supported - but I haven't found a system which supports
it yet.  It seems this HIMEM.SYS is probably limited to 64Mb also.

> So it seems that CWSDPMI is not seeing all 128MB.

The only hope here is to try a custom CWSDPMI build which might support the
extra memory by not loading HIMEM/EMM and ignoring the BIOS return size and
to pass the real size in via some other method.

One way to test the memory would be to boot clean, and run a DJGPP program
which would run a memory sizing test to make sure all 128Mb is addressable
in the hardware.  If that works, you could (even without a modified DJGPP)
use the memory mapping functions to allow access to the extra 64Mb as a
single non-pageable chunk of memory.

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