Function  25h  Set Interrupt Vector 
     Sets the address of the code DOS is to perform each time the specified 
     interrupt is invoked. 
entry   AH      25h 
	AL      int number to reassign the handler to 
	DS:DX   address of new interrupt vector 
return  none 
note 1) Registers are unchanged. 
     2) No error codes are returned. 
     3) The interrupt vector table for the interrupt number specified in AL 
	is set to the address contained in DS:DX. Use function 35h (Get Vector) 
	to get the contents of the interrupt vector and save it for later use. 
     4) When you use function 25 to set an interrupt vector, DOS 3.2 doesn't 
	point the actual interrupt vector to what you requested. Instead, it 
	sets the interrupt vector to point to a routine inside DOS, which does 
	this: 
		1. Save old stack pointer 
		2. Switch to new stack pointer allocated from DOS's stack pool 
		3. Call your routine 
		4. Restore old stack pointer 
	The purpose for this was to avoid possible stack overflows when there 
	are a large number of active interrupts. IBM was concerned (this was an 
	IBM change, not Microsoft) that on a Token Ring network there would be 
	a lot of interrupts going on, and applications that hadn't allocated 
	very much stack space would get clobbered.  
 
 

See also:

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