KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q78813: HIMEM.SYS Reports Loading A20 Handler X,Y

Article: Q78813
Product(s): Microsoft Disk Operating System
Version(s): MS-DOS:5.0
Operating System(s): 
Keyword(s): 
Last Modified: 21-NOV-1999

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft MS-DOS operating system version 5.0 
-------------------------------------------------------------------------------

SUMMARY
=======

If two numbers appear on the A20 handler message when HIMEM.SYS starts, the
second number refers to a delay that pertains to some IBM AT compatible
computers. This number is determined by HIMEM.SYS, and you cannot change it.

MORE INFORMATION
================

For example, if the following message is displayed when HIMEM.SYS starts

  Installed A20 handler number 7,2.

the first number, 7, refers to the machine number. You can change this number by
including the /MACHINE switch on the DEVICE command for HIMEM.SYS in your
CONFIG.SYS file.

The second number, 2, refers to a delay number that is relevant for certain IBM
AT compatible machines. You cannot specify the delay number; it is determined
automatically by HIMEM.SYS.

In the example above, the Toshiba A20 handler (machine number = 7) is installed
using delay number 2.

There are only three valid delay numbers: 0, 1, 2. Also, there are only specific
valid combinations of machine and delay numbers. A delay number of 0 is never
displayed; the absence of a delay number implies a delay number of 0.
(Therefore, "1" is equivalent to "1,0".) The following list details the valid
combinations of machine and delay numbers under MS-DOS 5.0. All machine numbers
not listed here are not associated with delay numbers.

Machine Code    Machine Number, Delay Number
------------    ----------------------------

at              1
at              1,1
at              1,2
toshiba         7,2
at1             11
at2             12,1
css             12,1
at3             13,2
philips         13,2

The following combinations identify identical A20 handlers:

11   = 1
12,1 = 1,1
13,2 = 1,2

If you specify /MACHINE:1 as a HIMEM.SYS parameter, HIMEM will automatically
attempt to determine which of the three delays is appropriate. However, if you
specify /MACHINE number 11, 12, or 13, HIMEM.SYS will not attempt to determine
the correct delay value. Instead, it will use the delay value as shown in the
previous table. For example, if you specify /MACHINE:11, HIMEM.SYS will use
machine number 1 ("at") with delay number 0.

These alternative values for "at" are useful only if you cannot load HIMEM.SYS on
an IBM AT compatible computer.

Additional query words: 5.00 noupd

======================================================================
Keywords          :  
Technology        : kbMSDOSSearch kbMSDOS500
Version           : MS-DOS:5.0

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.