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

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

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.

Step 2. Edit Your CONFIG.SYS File

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

   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 

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: 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.

• Microsoft MS-DOS "User's Guide," Chapter 6, "Making More Memory Available."



• Microsoft MS-DOS Help Command Reference, (type help at the MS-DOS command prompt).

Additional query words: appnote 6.00 5.00 6.20 dos

Keywords : msdos
Issue type :
Technology :

Article ID: Q96710

Last Reviewed:
December 14, 2000

Send to a friend

Provided by
Microsoft Product Support Services