Erratic Keyboard Behavior Using HIMEM.SYS (74730)

The information in this article applies to:
    Microsoft MS-DOS operating system 5.0
    Microsoft MS-DOS operating system 5.0a
    Microsoft MS-DOS operating system 6.0
    Microsoft MS-DOS operating system 6.2
    Microsoft MS-DOS operating system 6.21
    Microsoft MS-DOS operating system 6.22

This article was previously published under Q74730


You may encounter erratic keyboard behavior when using HIMEM.SYS driver on certain systems. Symptoms may include a variety of problems interpreting the state of the SHIFT, CAPS LOCK, NUM LOCK, ALT, and CTRL keys.

If you encounter this kind of problem, setting the /CPUCLOCK: switch to ON may alleviate the problem. If not, use the HIMEM /machine:xxxx switch to specify an alternative value for the A20 handler. Switches which have been found to be most likely are 11, 12, and 13 (in that order). These switches represent progressively longer delays in the switch state of the A20 line compared to the default handler 1.


Another workaround is to include the following line in your AUTOEXEC.BAT file.
   c:\dos\keyb us,,c:\dos\keyboard.sys
KEYB replaces the ROM BIOS INT 09h keyboard interrupt handler with its own routine. This may allow handling of the keyboard in a manner that does not conflict with A20 handling.

Modification Type: Major Last Reviewed: 5/12/2003
Keywords: KB74730