NOTE: For a detailed explanation of Himem.sys and warm and cold boots, see “Technical explanation of the messages” later in this document.

This problem is most often caused by the computer’s CPU using a nonstandard type of memory management. To resolve this problem, add the lines Device=A:\Himem.sys and Set DOS16M=2 to the Config.sys and Autoexec.bat files, respectively. See the section “How to edit the Config.sys and Autoexec.bat startup files” later in this document.

If adding those lines to the startup files does not resolve the problem, check the following possibilities:

• The Himem.sys file is not in the directory in which the computer expects to find it. 
  Make sure that Himem.sys is in the same directory as Ghost.exe or in the root of the bootable floppy disk from which you are running Ghost.
• The Config.sys file is attempting to load the Himem.sys file more than once.
  When the Config.sys file calls the Himem.sys file more than once, the computer can become confused. In this case, edit the Config.sys file to remove all references (calls) to Himem.sys except one.
• The Himem.sys file is damaged. 
  Delete the copy of Himem.sys from the bootable floppy disk, and replace it with a fresh copy from the same version of DOS.

How to edit the Config.sys and Autoexec.bat startup files
This procedure modifies the Config.sys and Autoexec.bat files to accommodate different types of memory handling used by the CPU. 

Since a variety of memory handling methods are in use, you may need to repeat this procedure several times to find the modification necessary for the particular CPU on your computer, as described in Step 9. 

To modify the startup files to accommodate different types of memory handling:

1. Restart the computer.
2. Do one of the following:
   For Windows 95: When the message “Starting Windows 95” appears, immediately press F8. The Windows 95 Startup Menu appears.
   For Windows 98: Hold down the Ctrl key after restarting the computer. The Windows 98 Startup menu appears.
3. Select Safe Mode – Command Prompt Only and press Enter. The C: prompt appears.
4. At the C: prompt, enter:

   EDIT Autoexec.bat

   The DOS Editor opens and displays the contents of the Autoexec.bat file.

5. At the beginning of the file, press enter to create a blank line, and then type the following line:

   SET DOS16M=2

   This command increases reserved memory blocks from 1 to 2.

6. Press Alt+F, then X to exit the DOS Editor. When prompted to save the changes, choose Yes and press Enter. The C: prompt appears.
7. At the C: prompt, enter:

   EDIT Config.sys

   The DOS Editor opens and displays the contents of the Config.sys file.

8. Locate the line loading Himem.sys. For example, it may read:

   DEVICE=C:\Windows\Himem.sys

   The name and location of the Windows program folder may be different on your computer.

9. At the end of the line, type a space, and then type the following:

   /M:1

   The line should now read:

   DEVICE=C:\Windows\Himem.sys /M:1

   If you do not have the Himem.sys line, add the line to the beginning of the file.

   Note that the /M:1 line depends upon the hardware version of the A20 handler. You may need to try the numbers 1-17 (for instance, /M:12) to find the correct version for the computer. PS/2 computers and Prolinea computers, for example, tend to require /M:2 instead of /M:1. 

10. Press Alt+F, then X to exit the DOS Editor. When prompted to save the changes, select Yes and press Enter.
11. Restart the computer. It should now start normally.

If the problem is still not resolved
If none of these procedures resolved the problem, there may be physical damage to some component of the computer, such as a bad memory chip. Resolution of such issues is beyond the scope of this document.

Technical explanation of A20 messages
Himem.sys is a DOS program that enables access to the first 64 KB of extended memory, called “high memory.” Although Windows is an operating system, it needs this file because Windows 3.x, Windows 95, and Windows 98 are not “standalone” operating systems. They require the Disk Operating System (DOS) to load and run.

During computer startup, the computer first starts up in DOS. Once DOS is loaded and the computer has access to high memory, Windows can then load. If the computer does not have access to high memory, Windows cannot load and the computer will display A20 messages.

The number A20 refers to the “line” of the CPU that must be enabled in order for Himem.sys to access the high memory area. The A20 error occurs when the A20 line is not enabled.

Warm boot
A “warm boot” means restarting the computer without first turning off the power. In DOS, a computer can be warm booted by using the Reset button or by pressing Ctrl+Alt+Del. 

Cold boot
A “cold boot” means starting the computer by turning on the power. Generally, after turning off the power, wait 5 to 30 seconds before turning on the power again. This allows time for the hard disk to fully power down before restarting it and time for old information to “drain” from the computer.