Important Notice

The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

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mov     ax, 1681h   ; Begin Critical Section
int     2Fh         ; multiplex interrupt
 
Begin Critical Section (Interrupt 2Fh Function 1681h) prevents Windows from
switching execution from the current VM to some other. MS-DOS device drivers
and TSRs use this function to prevent a task-switch from occurring.
 
Return Value
 
This function has no return value.
 
Comments
 
When a virtual machine is in a critical section, no other task will be
allowed to run except to service hardware interrupts. For this reason, the
critical section should be released using End Critical Section (Interrupt
2Fh Function 1682h) as soon as possible.
 
 
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