Q96710: How Do I Get MS-DOS to Run in the High Memory Area?
Article: Q96710
Product(s): Microsoft Disk Operating System
Version(s): MS-DOS:5.x,6.0,6.2,6.21,6.22
Operating System(s):
Keyword(s): msdos
Last Modified: 17-DEC-2000
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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
=======
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" (without the quotation marks)
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" (without the quotation marks)
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" (without the quotation marks)
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" (without the quotation marks)
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" (without the quotation marks)
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:" (without the quotation marks)
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:\ " (without the quotation marks)
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" (without the quotation marks)
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(R) 6300 Plus 5
Bull Micral 60 16
Chaplet 1
CompuAdd(R) 386 systems 1 or 8
CSS Labs 12
Datamedia 386/486 2
Everex(TM) AT Plus 1800 1
Everex Notebook ELX 1
Excel Computer Systems 13
Hitachi(R) HL500C 8
Hewlett-Packard(R) 14
(HP(R)) Vectra(R)
HP Vectra (A and A+) 4
IBM(R) PC/AT(R) 1, 11, 12, or 13
IBM PS/2(R) 2
Intel(R) 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(R) SX 9
Unisys(R) PowerPort 2
WYSE(R) 12.5 MHz 286 8
Zenith(R) 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(R) 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).
Additional query words: appnote 6.00 5.00 6.20 dos
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Keywords : msdos
Technology : kbMSDOSSearch kbMSDOS621 kbMSDOS622 kbMSDOS620 kbMSDOS600 kbMSDOS500 kbMSDOS500a
Version : MS-DOS:5.x,6.0,6.2,6.21,6.22
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