Software Interrupts

Windows NT uses software interrupts to schedule and execute certain kinds of deferred processing. A software interrupt is an event which behaves just like a "normal" interrupt, but is caused by the processor writing to some control register, rather than an external event. The 80x86 Int instruction generates a kind of trap, not a software interrupt, and thus is not adequate for this purpose.

Processors only send software interrupts to themselves. They are masked in the same way as other interrupts. Software interrupts have a priority lower than any I/O device.