When MS-DOS Fails to Load in the HMA (73293)

The information in this article applies to:
    Microsoft MS-DOS operating system 5.0
    Microsoft MS-DOS operating system 5.0a
    Microsoft MS-DOS operating system 6.0
    Microsoft MS-DOS operating system 6.2
    Microsoft MS-DOS operating system 6.21
    Microsoft MS-DOS operating system 6.22

This article was previously published under Q73293


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


High Memory Area is in Use


The first message, "64Kb High Memory Area is Available," is usually caused by not having the following line in the CONFIG.SYS file:
To correct this problem, add the DOS=HIGH 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 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

    If you are using MS-DOS 6.x, type help himem.sys at the MS-DOS command prompt, and then press ENTER.

Modification Type: Major Last Reviewed: 5/10/2003
Keywords: KB73293