HPET Support – The BIOS Optimization Guide

HPET Support - The BIOS Optimization Guide

HPET Support

Common Options : Enabled, Disabled

 

Quick Review of HPET Support

The HPET, short for High Precision Event Timer, is a new system timer developed by Intel and Microsoft to replace the four system timers currently in use.

Because of its higher precision and performance, it is naturally desirable to use the HPET instead of the older system timers. However, older operating systems do not support HPET. This is where the HPET Support BIOS option comes in.

Setting it to Enabled allows the operating system and applications to use the High Precision Event Timer (HPET) for higher precision and better performance.

Setting it to Disabled disables the High Precision Event Timer (HPET). The operating system and applications will use the older system timers instead.

If you are using a newer operating system like Windows Vista or Windows 2008, you should enable the HPET Support BIOS option. Other operating systems that support HPET include Linux 2.6, FreeBSD and x86 versions of Mac OS X.

If you are using an older operating system like Windows XP or Windows Server 2003, you should disable this BIOS option.

 

Details of HPET Support

The HPET, short for High Precision Event Timer, is a new system timer developed by Intel and Microsoft to replace the four system timers currently in use :

  • the 8254 Programmable Interval Timer (PIT),
  • the Real Time Clock (RTC),
  • the Advanced Programmable Interrupt Controller (APIC) timer and
  • the PM clock (or ACPI timer).

The HPET was originally called the Multimedia Timer (MM Timer) but they changed it to its current name to avoid confusion with a Microsoft DirectX timer of the same name, as well as to better describe the timer.

The HPET is also designed to provide aperiodic functionality and higher precision, both necessary to support the tighter timing requirements of multimedia and other time-sensitive applications. High-definition video playback, for example, requires a timing resolution of 1 millisecond to decode and synchronize the video frames and audio streams.

The aperiodic functionality allows applications to issue commands “out of sync” with the system timer. This allows the application to achieve much greater precision without the need for the system timer to actually issue the clock interrupts at the frequency required to achieve that precision. By allowing the system timer to run at a much lower frequency, this feature improves system performance and in mobile systems, extends battery life.

The higher precision is afforded by the HPET’s higher frequency of at least 10 MHz, which gives it a granularity of 1 microsecond or less. Its aperiodic functionality though ensures a nanosecond level of accuracy. It also has registers that are at least 32-bits wide. Some HPETs have 64-bits wide registers which can also run in the 32-bit mode.

Because of its higher precision and performance, it is naturally desirable to use the HPET instead of the older system timers. However, older operating systems do not support HPET. This is where the HPET Support BIOS option comes in.

Setting it to Enabled allows the operating system and applications to use the High Precision Event Timer (HPET) for higher precision and better performance.

Setting it to Disabled disables the High Precision Event Timer (HPET). The operating system and applications will use the older system timers instead.

If you are using a newer operating system like Windows Vista or Windows 2008, you should enable the HPET Support BIOS option. Other operating systems that support HPET include Linux 2.6, FreeBSD and x86 versions of Mac OS X.

If you are using an older operating system like Windows XP or Windows Server 2003, you should disable this BIOS option.

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