High Precision Event Timer: Formerly known as Multimedia Timer, this specification provides register and programming interface definitions for event timer hardware which can be used on Intel® architecture-based personal computers. This specification outlines new timer hardware for system software when generating interrupts for thread schedulers, kernels, and multimedia timer servers. It is intended to initially supplement and eventually replace the legacy 8254 Programmable Interval Timer (PIT) and legacy Real Time Clock (RTC) interrupt-driven hardware.

You use a Windows Vista-based computer that supports High Precision Event Timer (HPET), and the computer runs for several hours. Then, you may notice that the system time differs from the BIOS time by several seconds.