System Interval Timer Interrupt

Windows NT requires a system interval timer to provide periodic interrupts, which are used for updating of the system clock, and for time-slice processing. All processors must receive the interrupts, and they must use the same vector on all processors. They do not need to be synchronized. Either a single clock that distributes an interrupt to all processors or a per-processor local clock that interrupts only its own processor may be used.

The clock should have a period in the range from 1 to 10 milliseconds. The period of the clock should be such than an integer number of clock pulses occur each second (e.g. 1000 pulses per second, not 1000.4 pulses per second). Inaccuracies in this clock will cause the system time of day clock to be inaccurate as well.