DOSSWAP.EXE Problem Occurs When Swap Not Allowed (73737)

The information in this article applies to:
    Microsoft MS-DOS operating system 5.0

This article was previously published under Q73737


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.


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.

Modification Type: Major Last Reviewed: 11/23/1999
Keywords: KB73737