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Q73293: When MS-DOS Fails to Load in the HMA

Article: Q73293
Product(s): Microsoft Disk Operating System
Version(s): MS-DOS:5.0,5.0a,6.0,6.2,6.21,6.22
Operating System(s): 
Keyword(s): 
Last Modified: 19-NOV-1999

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The information in this article applies to:

- Microsoft MS-DOS operating system versions 5.0, 5.0a, 6.0, 6.2, 6.21, 6.22 
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SUMMARY
=======

MS-DOS version 5.0 and 6.0 can save memory by loading itself into the first 64K
of extended memory, the high memory area (HMA). To check whether MS-DOS has
loaded itself in the HMA, issue the MEM command and look at the output. If the
last line of output reads

  MS-DOS is resident in High Memory Area

then MS-DOS has loaded itself into the HMA. However, if MS-DOS has failed to load
into the HMA, you will get one of two messages:

  64Kb High Memory Area is Available

  -or-

  High Memory Area is in Use

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

The first message, "64Kb High Memory Area is Available," is usually caused by
not having the following line in the CONFIG.SYS file:

  DOS=HIGH

To correct this problem, add the "DOS=HIGH" (without the quotation marks) line to
CONFIG.SYS.

The second message, "High Memory Area is in Use," has two possible causes:

- Something else is being loaded into the HMA, such as a network driver or some
  other application. If you want to run MS-DOS in the HMA instead of the
  program that is currently using it, you must disable the ability of the other
  program to use the HMA. Consult that program's documentation for the disable
  procedure. Then, you will need to add the line "DOS=HIGH" (without the
  quotation marks) to your CONFIG.SYS file and ensure that you are loading
  HIMEM.SYS.

- HIMEM.SYS is using the incorrect A20 handler. Upon installation, HIMEM.SYS
  usually selects one of 16 different A20 handlers, depending upon the hardware
  it detects. HIMEM's automatic detection can be overridden by the /MACHINE: or
  /M: switch. If HIMEM.SYS is installing the wrong A20 handler on its own, you
  must force it to install the correct handler with the /MACHINE: switch.
  However, if HIMEM.SYS is being forced to install an incorrect A20 handler by
  the /MACHINE: switch, you may be able to solve the problem by removing the
  /MACHINE: switch and allowing HIMEM to select which A20 it uses.

  For more information on MS-DOS 5.0's HIMEM.SYS and the /MACHINE: switch, see
  pages 610-613 of the version 5.0 "Microsoft MS-DOS User's Guide and
  Reference," or query on the following words:

  " HIMEM and /M and MS-DOS " (without the quotation marks)

  If you are using MS-DOS 6.x, type "help himem.sys" (without the quotation
  marks) at the MS-DOS command prompt, and then press ENTER.

Additional query words: 6.22 5.00 5.00a 6.00 6.20

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Keywords          :  
Technology        : kbMSDOSSearch kbMSDOS621 kbMSDOS622 kbMSDOS620 kbMSDOS600 kbMSDOS500 kbMSDOS500a
Version           : MS-DOS:5.0,5.0a,6.0,6.2,6.21,6.22

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