10-26-2015
The UNIX clock/timer interrupt
The book The Design of the Unix Operating System speaks of a clock or timer that is used in scheduling. The clock generates interrupts that update priority information for processes and preempt processes in a round-robin fashion. It's apparent that this "clock" is not the same thing as the CPU clock, since is only generates 50 to 100 signals every second, as opposed to millions or billions of pulses a second. It's also apparent that it's not the same thing as the mechanism that keeps track of the date - that is to say, the number of seconds since midnight before January 1, 1970. So what exactly is it? Is it a pulse generator? Does it store a value that increments? Is it synced with the CPU clock somehow? How does it work? And how can it be "reset"?
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