[ntp:questions] Re: Regular 16ms jump of NTP on Windows XP SP2

Terje Mathisen terje.mathisen at hda.hydro.com
Thu Sep 7 06:00:10 UTC 2006

Bert Gøtterup Petersen wrote:
> When running Windows I see a spike of about 16ms in the loopstats-files on 
> all the Windows nodes. 
> The peculiar thing is that the spike occurs every 24 hours and 15 minutes 
> per machine, but not at the same time on different machines.

Hmmm. Could this be an internal windows OS counter wrapping around?

24 hours + 15 min = 86400 + 900 = 87300 s

The original keyboard timer chip which generates the Dos 55 ms timer 
tick had a 64 K period which was close to but not exactly one hour...

87300 / (24 * 65536) = 0.055038

Yes! This is the original DOS timer tick period which Windows is still 
emulating for anything running inside a Dos box, as well as programs 
using very old Windows APIs.

I'm willing to bet that the spike is caused by a once/day fixup of any 
residual errors caused by the fact that this emulation isn't totally 

- <Terje.Mathisen at hda.hydro.com>
"almost all programming can be viewed as an exercise in caching"

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