Comparison To Predecessors
HPET is meant to supplement and replace the 8254 programmable interval timer and the RTC's periodic interrupt function. Compared to these older timer circuits, the HPET has higher frequency (at least 10 MHz) and wider 64-bit counters (although they can be driven in 32-bit mode).
While 8254 and RTC can, similarly to HPET, be put in one-shot mode, the set-up process is so slow that their one-shot mode is not used in practice for tasks requiring precise scheduling. Instead, 8254 and RTC are typically used in periodic mode with very small time interval. For example, if an application needs to perform several short (some milliseconds, perhaps) waits, it is better to have a periodic timer running constantly with 1 ms period because of the high setup cost of an 8254 or RTC one-shot timer. This causes an interrupt on every millisecond even if the application needs to do actual work less frequently. With HPET, the extra interrupts can be avoided, because the set-up cost of a HPET one-shot timer is considerably smaller.
Read more about this topic: High Precision Event Timer
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