Q77219: XMS Memory Is Not Reported Until Accessed

Article: Q77219
Product(s): Microsoft Disk Operating System
Version(s): MS-DOS:5.0
Operating System(s): 
Keyword(s): msdos
Last Modified: 22-NOV-1999

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft MS-DOS operating system version 5.0 
-------------------------------------------------------------------------------

SUMMARY
=======

XMS (extended memory specification) memory may not be reported by the MEM
command, even if HIMEM.SYS is properly loaded and extended memory is available.
XMS memory will not be reported until it has been accessed.

MORE INFORMATION
================

To reproduce this result, create a CONFIG.SYS file as follows:

     device=c:\dos\himem.sys
     files=30
     buffers=10
     shell=c:\dos\command.com c:\dos\ /p

and AUTOEXEC.BAT as follows:

     echo off
     prompt $p$g
     path=c:\dos;c:\ 

If you boot your computer with 2 MB of extended memory and the above
configuration and immediately run the MEM.EXE command, note that MEM will report
the following:

  2097152 bytes total contiguous extended memory
  2097152 bytes available contiguous extended memory

Because no program has yet accessed XMS memory, no XMS memory will be reported.
As soon as an XMS "user" (for example, DOS=HIGH, SMARTDRV.SYS) is loaded, all of
the contiguous extended memory will be reported as available XMS memory, less
the 64K high memory area (HMA) controlled by HIMEM.SYS itself.

Additional query words: 5.00 noupd

======================================================================
Keywords          : msdos 
Technology        : kbMSDOSSearch kbMSDOS500
Version           : MS-DOS:5.0

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.