DOCUMENT:Q73737  23-NOV-1999  [msdos]
TITLE   :DOSSWAP.EXE Problem Occurs When Swap Not Allowed
PRODUCT :Microsoft Disk Operating System
PROD/VER:MS-DOS:5.0
OPER/SYS:
KEYWORDS:msdos

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

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

SUMMARY
=======

There is a problem in MS-DOS version 5.0 Task Swapper that can cause mysterious
failures after a task switch request is not allowed.

A task switch request is prevented whenever you attempt to switch tasks by
pressing ALT+TAB or ALT+ESC when task switching could cause a problem for the
application. When the request is prevented, the machine beeps, and the task
switch does not occur.

If you find that erratic behavior occurs after you are not allowed to perform a
task switch, you should obtain the above application note.

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

A task switch request is disallowed under the following circumstances:

 - If you are running an application that is MS-DOS Shell Task Switcher aware
   and you press ALT+TAB to switch, Task Swapper may disallow the call because
   the application has notified MS-DOS Shell not to swap it. For example, Novell
   NetWare never allows task switches while it is servicing any MS-DOS function
   (INT 21) call over the network.

 - If you run any application that uses netBIOS asynchronous API (for example,
   VTP or an SQL application in a session), Task Swapper automatically disallows
   any switch request to avoid possible problems.

In either of the above cases, the value in the CX register will be destroyed. The
affect of the CX register being destroyed will vary, depending on what the
application was storing there.

Additional query words: appnote 5.00 dosshell dosswap kbfest

======================================================================
Keywords          : msdos 
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.

Copyright Microsoft Corporation 1999.