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

David J Taylor david-taylor at blueyonder.delete-this-bit.and-this-part.co.uk.invalid
Thu Jan 21 20:52:33 UTC 2010

> 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.

Evandro, thanks for the details.  I've never worried about the precision 
of the QueryPerformanceCounter function in my own software, I'm just 
reporting the values as a clue to why we see NTP behaving as it does.

BTW: I still have systems running which are older than Core2, on still has 
an Intel PIII 550MHz (and keeps good time as a stratum-1 server with 
Windows 2000).


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