Missing Himem.sys or A20 error in Windows95 or 98
by Roxanne Pierce
When you reboot the computer, it displays one of the following (or
- "Windows XMS driver Unable to control A20 line; XMS
driver not installed."
- "HIMEM.SYS is missing."
This error message does not appear when first applying power to the
computer, only when rebooting it once it is already powered on. It is more likely to
affect laptop computers than desktop computers. This error message will frequently appear
for the first time after installing one of several versions of Norton Anti-Virus.
Turn the computer off completely, then follow these steps to make changes to the
computer's DOS startup files, autoexec.bat and config.sys:
Press Alt+F to open the File menu. Choose Exit and press Enter. When prompted to save
changes, answer Yes and press Enter.
Reboot the computer. It should now boot normally.
- Turn on the computer.
- For Windows 95 When the screen says
"Starting Windows 95", immediately press the F8 key. This displays the Windows
95 Startup Menu. For Windows 98: as soon as
you turn on the computer, press and hold the CTRL key until the Windows 98 Startup Menu is
- Select Safe Mode - Command Prompt Only either by highlighting that option with your down
arrows or by typing in the number of that menu option, and then press the Enter key on
- At the C:\> prompt, type EDIT AUTOEXEC.BAT [Enter]
- You should now have a blue screen which you can edit text in. At the very top of the
window, add the following line SET DOS16M=2
- Press Alt+F to open the File menu. Choose Exit and press the Enter key.
- When prompted to save changes, use your arrow keys to highlight "Yes" and
- You will now be back at the C:\> prompt. Type EDIT CONFIG.SYS [Enter]
- In the text editor, find a line which refers to a file called HIMEM.SYS and add
the very end of that line. Be sure there is a space following the end of the existing line
and the /M:1
- If you do not have a HIMEM.SYS line, add the following line:
Note1 You may need to
alter the path if your version of Windows 95 or Windows 98 is not located in the Windows
Note2 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.
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