Clock tick multiplied by 232 613 Programmable Interval Timer

Besides the Real Time Clock and the Time Stamp Counter, IBM-compatible PCs include another type of time-measuring device called Programmable Interval Timer (PIT ). The role of a PIT is similar to the alarm clock of a microwave oven: it makes the user aware that the cooking time interval has elapsed. Instead of ringing a bell, this device issues a special interrupt called timer interrupt, which notifies the kernel that one more time interval has elapsed. 12! Another difference from the alarm clock is that the PIT goes on issuing interrupts forever at some fixed frequency established by the kernel. Each IBM-compatible PC includes at least one PIT, which is usually implemented by a 8254 CMOS chip using the 0x40-0x43 I/O ports.

Continue reading here: [2The PIT is also used to drive an audio amplifier connected to the computers internal speaker

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