[ntp:questions] NTP on Windows Server 2008 R2

Geir Guldstein dont-spam-geir.guldstein at gmail.com
Wed Feb 8 17:45:54 UTC 2012

> 1 - You could try setting the /system/ environment variable
> NTPD_USE_SYSTEM_CLOCK to "1" (or any value)
> as this will force use of the native clock (to force off interpolation).
> However, I'm not sure which version of NTP introduced this feature.
> 2 - I'm using NTP 4.2.7p241 which has produced excellent results on
> Windows, so you may also like to try that.

Thanks David.

Regarding 1: 4.2.6p5 supports NTPD_USE_SYSTEM_CLOCK. However, I don't 
think that it will make any difference. I see in the source code 
(nt_clockstuff.c) that the event log message "using Windows clock 
directly" (which I get in the case where NTP does *not* work properly) 
indicates that ntpd already has disabled interpolation. Note that this 
message is not generated in the case where NTP works reasonably well, 
which means that it does use interpolation in this case.

The event log messages indicate that the device driver changes the 
system clock's resolution:
Without device driver installed: "Windows clock precision 15.600 msec, 
min. slew 6.410 ppm/s"
With device driver installed: "Windows clock precision 0.500 msec, min. 
slew 6.410 ppm/s"
In nt_clockstuff.c I see that it is this precision that makes NTP decide 
to enable or disable interpolation if no environment variables have been 
set to control it.

Regarding 2: Thanks, I will try 4.2.7p241.


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