Author: Jeremiah Penery
Date: 21:28:42 11/09/04
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Maybe this helps some, it was posted in another forum by a MSFT Online Support Partner: http://www.talkaboutsoftware.com/group/microsoft.public.win32.programmer.kernel/messages/87257.html Fundamentally, Windows has no concept of time *other* than an interrupt (the Time/Scheduling interrupt) that fires every 10 milliseconds. [15ms on multiprocessor system(?)] - Windows uses the scheduler interrupt to update its own internal clock. - The CPU does not have a clock to tell "how much time since the last interrupt" * Some new CPUs *do* have an internal clock, but Windows can not rely on new CPUs. - QueryPerformanceCounter() relies on hardware inside the ACPI chipset. This functionality only exists on ACPI hardware, so Windows can not rely on it. Basically, hardware limitations force this architecture. When a thread calls Sleep(), Windows can not tell if it used 1 nanosecond or 9.99 milliseconds of its quantum.
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