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The High Precision Event Timer (HPET) is a hardware timer used in personal computers. It was developed jointly by Intel and Microsoft and has been incorporated in PC chipsets since circa 2005. Formerly referred to by Intel as a Multimedia Timer,〔 the term HPET was selected to avoid confusion with the multimedia timers as a software feature introduced in the MultiMedia Extensions to Windows 3.0.〔(【引用サイトリンク】title=Multimedia Timers )〕 Older operating systems that do not support a hardware HPET device can only use older timing facilities, such as the programmable interval timer (PIT) or the real-time clock (RTC). Windows XP, when fitted with the latest HAL (hardware abstraction layer), can also use the processor's Time Stamp Counter (TSC) or Power Management Timer (PMTIMER), together with the RTC to provide operating system features that would, in later Windows versions, be provided by the HPET hardware. Confusingly, such Windows XP systems quote "HPET" connectivity in the device driver manager even though the Intel HPET device is not being used. ==Features== An HPET chip consists of a 64-bit up-counter (main counter) counting at a frequency of at least 10 MHz, and a set of (at least three, up to 256) comparators. These comparators are 32- or 64-bit wide. The HPET is programmed via a memory mapped I/O window that is discoverable via ACPI. The HPET circuit in modern PCs is integrated into the southbridge chip. Each comparator can generate an interrupt when the least significant bits are equal to the corresponding bits of the 64-bit main counter value. The comparators can be put into one-shot mode or periodic mode, with at least one comparator supporting periodic mode and all of them supporting one-shot mode. In one-shot mode the comparator fires an interrupt once when the main counter reaches the value stored in the comparator's register, while in the periodic mode the interrupts are generated at specified intervals. Comparators can be driven by the operating system, e.g. to provide one timer per CPU for scheduling, or by applications. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「High Precision Event Timer」の詳細全文を読む スポンサード リンク
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