[ntp:questions] Timekeeping broken on Windows XP with multimedia timer enabled (-M option)

Evandro Menezes evandro at mailinator.com
Thu Jan 21 16:00:36 UTC 2010

On Jan 21, 9:51 am, "David J Taylor" <david-tay... at blueyonder.delete-
this-bit.and-this-part.co.uk.invalid> wrote:
> Thanks, Martin.  I'm beginning to wish I'd never asked, as I have Windows
> XP SP3 here and yet the performance counter is running at 2.4GHz (Intel
> E6600 dual-core).  Or does the PM_Timer only apply to AMD systems?

Windows chooses the most precise, invariant frequency source available
in the system.  As I said before, Intel's Core2 processors have a TSC
that doesn't vary with the CPU clock (though its precision is not as
good as it seems).  Only newer AMD processors sport the same feature
and even then it must be enabled by a BIOS option that's not always
available.  Therefore, the likelihood of an AMD system using the PM
timer is greater than new Intel systems.

In these days, it's moot to worry about the precision of the
QueryPerformanceCounter function.  Windows will use the most precise
time source in the system and only very old systems would not have at
least the PM timer.


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