  
PSS ID Number: Q96710
Article last modified on 12-04-1995
PSS database name: MSDOS
 
5.x 6.00 6.20 6.21 6.22
 
MS-DOS
 
How to load MS-DOS into the High Memory Area.

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The information in this article applies to:
 
 - Microsoft MS-DOS operating system versions 5.x, 6.0, 6.2, 6.21, 6.22
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SUMMARY
=======
 
Microsoft MS-DOS can conserve memory by loading itself into the first 64
kilobytes (K) of extended memory, known as the high memory area (HMA).
MS-DOS can load itself into the HMA if your computer has an 80286 or higher
processor, extended memory, and is configured correctly.
 
This article provides guidelines for configuring your system so that
MS-DOS can successfully load into the HMA.
 
MORE INFORMATION
================
 
To find out whether MS-DOS has loaded into the HMA, type the following
at the MS-DOS command prompt:
 
   mem
 
MS-DOS displays information about your system's memory. If the last
line of the display reads "MS-DOS is resident in the High Memory
Area," MS-DOS has successfully loaded into the HMA.
 
If MS-DOS fails to load into the high memory area, follow the
procedures below in the order presented.
 
Step 1. Make Sure Your System Meets the Prerequisites
-----------------------------------------------------
 
1. Make sure your system has an 80286 or higher processor.
 
2. Make sure your computer has extended memory. (MS-DOS cannot load
   into expanded memory.) To find out, type the following at the
   MS-DOS command prompt:
 
      mem
 
   The MEM command reports the type and amount of memory that your
   computer has.
 
NOTE: If your system does not meet these requirements, you cannot
load MS-DOS into the HMA.
 
Step 2. Edit Your CONFIG.SYS File
---------------------------------
 
Edit your CONFIG.SYS file to be sure that it contains all required
statements.
 
1. Open your CONFIG.SYS file in a text editor. For example, to edit
   the file with MS-DOS Editor, type the following at the MS-DOS
   command prompt:
 
      edit <drive>:\config.sys
 
   where <drive> is the drive containing your CONFIG.SYS file.
 
2. Make sure your CONFIG.SYS file contains a DEVICE command for
   HIMEM.SYS. If the file doesn't contain one, insert the following
   line at the beginning of the file:
 
      device=<drive>:\dos\himem.sys
 
   where <drive> is the drive containing your MS-DOS directory.
 
3. Make sure your CONFIG.SYS file contains a DOS=HIGH command or a
   DOS=HIGH, UMB command. If the file doesn't contain one of these
   commands, insert the following line:
 
      dos=high
 
4. If you are using MS-DOS Editor, choose Exit from the File menu. When
   MS-DOS Editor displays a dialog box prompting you to save your
   file, choose the Yes button or press ENTER.
 
5. Restart your computer by pressing CTRL+ALT+DEL.
 
6. Use the MEM command to find out whether MS-DOS loaded successfully
   into the HMA. If MS-DOS failed to load into the HMA, continue with
   the next procedure.
 
Step 3. Add the /CPUCLOCK Switch
--------------------------------
 
1. If you are using MS-DOS 5.x or earlier, you need to create an MS-DOS
   startup disk. To do so, insert a formatted floppy disk in drive A and
   type the following:
 
      sys <drive>: a:
 
   where <drive> is the drive containing your MS-DOS directory.
 
   NOTES:
 
   - Do not use drive B when you create a startup disk. Most computer
     BIOS startup procedures do not look for a disk in drive B when
     starting the computer (even though the light on drive B may turn
     on momentarily).
 
   - If you are using MS-DOS 6.0 or 6.2, you can skip to step 3. You
     do not need to create a startup floppy disk because you can use
     the MS-DOS interactive startup key (F8) to bypass commands in
     your CONFIG.SYS file if they cause your system to stop responding
     (hang). For more information on using interactive startup, see
     the "MS-DOS User's Guide," for version 6.
 
2. Copy your CONFIG.SYS file to the startup disk by typing the
   following:
 
      copy <drive>:\config.sys a:\
 
   where <drive> is the drive containing your CONFIG.SYS file.
 
3. Use MS-DOS Editor to open your original CONFIG.SYS file. Locate the
   DEVICE command for HIMEM.SYS and add the /CPUCLOCK:ON switch to it.
   The command should now appear similar to the following:
 
      device=c:\dos\himem.sys /cpuclock:on
 
4. Save your CONFIG.SYS file.
 
5. Restart your computer by pressing CTRL+ALT+DEL.
 
6. Use the MEM command to find out whether MS-DOS has loaded
   successfully into the HMA. At the MS-DOS command prompt, type:
 
      mem
 
   If MS-DOS has failed to load into the HMA, continue with the next
   procedure.
 
Step 4. Add the /MACHINE Switch
-------------------------------
 
The /MACHINE switch specifies the type of computer you have. The
following table lists machine types in alphabetical order, and shows
the number to specify with the /MACHINE switch:
 
   Machine Type               Number
   ----------------------------------------------
 
   Abacus 386                 1
   Acer 1100                  6
   AT&T® 6300 Plus          5
   Bull Micral 60             16
   Chaplet                    1
   CompuAdd® 386 systems    1 or 8
   CSS Labs                   12
   Datamedia 386/486          2
   Everex™ AT Plus 1800    1
   Everex Notebook ELX        1
   Excel Computer Systems     13
   Hitachi® HL500C          8
   Hewlett-Packard®         14
      (HP®) Vectra®
   HP Vectra (A and A+)       4
   IBM® PC/AT®            1, 11, 12, or 13
   IBM PS/2®                2
   Intel® 301z or 302       8
   JDR 386/33                 1
   OPT 386-25 motherboard     1
   Pak 386SX                  1
   PC Limited                 4
   PC 380/33C, PC 350/33C,    2
      or PC300/33C BIOS
      revision 1.14
   Philips                    13
   Phoenix Cascade BIOS       3, 1, or 8
   Toshiba 1600 and 1200XE    7
   Toshiba 5100               7
   Tulip® SX                9
   Unisys® PowerPort        2
   WYSE® 12.5 MHz 286       8
   Zenith® ZBIOS            10
 
To add the /MACHINE switch, follow these steps:
 
1. Since using the wrong /MACHINE switch can cause your system to
   stop responding (hang), you should make an MS-DOS bootable system
   disk before changing the /MACHINE switch. To do this, put a
   formatted floppy disk in drive A and use the SYS program to
   transfer the system files from your boot drive. For example, if
   your boot drive is C, type "sys c: a:" (without the quotation
   marks) at the MS-DOS command prompt, and then press ENTER.
 
2. Use a text editor, such as MS-DOS Editor, to open your CONFIG.SYS
   file.
 
3. Locate the DEVICE command for HIMEM.SYS, and add the /MACHINE
   switch and the number from the table above that corresponds to your
   hardware. The switch should be followed by a colon (:) and your
   machine number. For example, the following DEVICE command specifies
   a Toshiba® 5100:
 
      device=c:\dos\himem.sys /cpuclock:on /machine:7
 
   NOTE: If your computer is not on the list, or you are not sure
   which number to use, try machine numbers in the following order:
   1, 11, 12, 13, 8, 2-10, 14-16.
 
4. Save your CONFIG.SYS file.
 
5. Restart your computer by pressing CTRL+ALT+DEL.
 
   If your computer fails when you restart it, or you see the "ERROR:
   Unable to control A20 line!" message, the machine number you
   specified is incorrect for your hardware. If the computer hangs and
   you are using MS-DOS 5.0, insert the bootable system disk in drive A
   and restart your system. If you are using MS-DOS 6.0 or 6.2, use the
   F8 key to start the interactive startup procedure. When you are
   prompted to load HIMEM.SYS, press the N key.
 
   Then, edit your CONFIG.SYS file, specify a different machine
   number, save your changes, and restart your system. You may need to
   try several machine numbers before you identify the one that works
   for your computer.
 
6. After your computer starts, use the MEM command to find out whether
   MS-DOS loaded into the HMA. If it did not, repeat this procedure
   and specify a different machine number.
 
REFERENCES
==========
 
If you are using MS-DOS 5.0, refer to the following sources for
additional information:
 
 - Microsoft MS-DOS "User's Guide and Reference," page 282, which
   explains how to load MS-DOS into the HMA.
 
 - Microsoft MS-DOS "User's Guide and Reference," pages 610-613,
    which provides details about the HIMEM.SYS device driver.
 
If you are using MS-DOS 6.0 or 6.2, refer to the following sources for
additional information:
 
 - Microsoft MS-DOS "User's Guide," Chapter 6, "Making More Memory
   Available."
 
 - Microsoft MS-DOS Help Command Reference, (type "help" [without the
   quotation marks] at the MS-DOS command prompt).
 
KBCategory: kbtool kbdisplay kbfile kbappnote
KBSubcategory: msdos
Additional reference words: appnote 6.00 5.00 6.20 dos
=============================================================================
Copyright Microsoft Corporation 1995.


 
