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.
HTH
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).
Cheers,
David
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