Message-ID:	<001d01c0f06b$963693e0$1308e289@mpaul>
From:	"Matthias Paul" <Matthias DOT Paul AT post DOT rwth-aachen DOT de>
To:	<opendos AT delorie DOT com>
Subject:	Strange XMS issue using MS HIMEM.SYS
Date:	Sat, 9 Jun 2001 00:36:29 +0200
Organization:	University of Technology, RWTH Aachen, Germany
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Reply-To:	opendos AT delorie DOT com

Hi,

I have just encountered a strange phenomenon using
the MS-DOS HIMEM.SYS when switching between
DR-DOS 7.03 and MS-DOS 7.10.

It appears that the MS-DOS HIMEM.SYS reports
4 Kb less available extended memory when loaded
under MS-DOS 7.10 compared to the available
extended memory when loaded under DR-DOS 7.03
or MS-DOS 6.22.

At the same time, the start address of the memory
is 4 Kb higher (1024 Kb+64 Kb+4Kb) than under
DR-DOS 7.03 or MS-DOS 6.22 (1024 Kb+64 Kb).

This occurs with both, the HIMEM.SYS from
MS-DOS 6.22 as well as with the driver from
MS-DOS 7.10. (Of course, the 6.22 HIMEM.SYS
only supports up to 64 MB of memory. [1 Mb=
1024Kb=1024*1024 bytes])

In all cases, I am using the DR-DOS EMM386
/VERBOSE=DEBUG option to display the
amount of XMS memory provided by the
HIMEM.SYS driver.

I am loading the drivers at the start of DCONFIG.SYS/
CONFIG.SYS/CONFIG.DOS files:

DEVICE?=c:\dos\msdos\msdos.622\himem.sys /testmem:on /verbose
DEVICE?=c:\windows\himem.sys /testmem:on /verbose
DEVICE=c:\dos\drdos\drdos.703\emm386.exe /video /multi /dpmi ...
  ... /exclude=c000-c7ff,c800-c8ff /use=c900-efff /frame=auto ...
  ... /rom=c000-c7ff,c800-c8ff,f000-ffff /handles=128 ...
  ... /verbose=debug
Note: The /frame=e800 option is not, and the /use=f000-f7ff option
      seems not to be compatible with the Windows 9x GUI.
      MS EMM386.EXE does not provide this feature, anyway.

Here are my results (on an ASUS P55T2P4 Rev.3.10 430HX
mainboard with Award 4.51PG Flash BIOS 2.07-2, equipped
with 256 Mb of physical memory):

DR-DOS 7.03:

No HIMEM.SYS, but DR 7.03 EMM386.EXE:
03FE0000 @ 00110000 ->
64Mb-128Kb @ 1024Kb+64Kb=1088Kb

MS 6.22 HIMEM.SYS + DR 7.03 EMM386.EXE:
03FE0000 @ 00110000 ->
64Mb-128Kb @ 1024Kb+64Kb=1088Kb

MS 7.10 HIMEM.SYS + DR 7.03 EMM386.EXE:
0FEF0000 @ 00110000 ->
256Mb-1088Kb @ 1024Kb+64Kb=1088Kb


MS-DOS 6.22:

No HIMEM.SYS + DR 7.03 EMM386.EXE:
03FE0000 @ 00110000 ->
64Mb-128Kb @ 1024Kb+64Kb=1088Kb

MS 6.22 HIMEM.SYS + DR 7.03 EMM386.EXE:
03FE0000 @ 00110000 ->
64Mb-128Kb @ 1024Kb+64Kb=1088Kb

MS 7.10 HIMEM.SYS + DR 7.03 EMM386.EXE:
0FEF0000 @ 00110000 ->
256Mb-1088Kb @ 1024Kb+64Kb=1088Kb


MS-DOS 7.10 (98SE):

No HIMEM.SYS, but DR 7.03 EMM386.EXE:
03FE0000 @ 00110000 ->
64Mb-128Kb @ 1024Kb+64Kb=1088Kb

MS 6.22 HIMEM.SYS + DR 7.03 EMM386.EXE:
03FDF000 @ 00111000 ->
64Mb-128Kb-4Kb @ 1024Kb+64Kb+4Kb=1088Kb+4Kb=1092Kb

MS 7.10 HIMEM.SYS + DR 7.03 EMM386.EXE:
0FEEF000 @ 00111000 ->
256Mb-1088Kb-4Kb=256Mb-1092Kb @
1024Kb+64Kb+4Kb=1088Kb+4Kb=1092Kb

This shows that the MS HIMEM.SYS drivers appear
to allocate a fixed area of 4 Kb just after the HMA
when run on MS-DOS 7.10 (maybe 7.0 as well???),
but not when run under MS-DOS 6.22 (or DR-DOS 7.03
which reports itself as DOS 6.0).

I would be very interested to known if others can
reproduce this behaviour on their systems, in particular
in comparision with PC DOS, MS-DOS before 6.22,
MS HIMEM.SYS drivers before 6.22 (3.10 as of
1993-09-30). What happens with MS-DOS 7.0?
Does anybody have an idea if this might be just a
strange artefact in MS HIMEM.SYS or if it serves
some currently unknown purpose...

Greetings,

 Matthias

-- 

Matthias Paul, Ubierstrasse 28, D-50321 Bruehl, Germany
<mailto:Matthias DOT Paul AT post DOT rwth-aachen DOT de>; <mailto:mpaul AT drdos DOT org>
http://www.uni-bonn.de/~uzs180/mpdokeng.html; http://mpaul.drdos.org

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