[ntp:questions] Slow convergence of NTP with GPS/PPS

David Woolley david at ex.djwhome.demon.co.uk.invalid
Wed Oct 22 06:30:22 UTC 2008

Richard B. Gilbert wrote:

> The clock in a PC is basically the guts of a cheap "Quartz" watch.  It 
> wouldn't surprise me if the manufacturers bought the crystals rejected 
> by the watch makers.  I suspect that the clock exists MOSTLY so the 
> machine will have the correct date for things like letters and checks.

That describes the RTC, and may not even be valid for HPET systems.  The 
clock that ntpd disciplines is not based on a 32kHz watch crystal, but 
on a much higher frequency crystal.  Historically, the primary purpose 
of the latter crystal is to provide a logic clock for the processor and 
memory, not for time keeping.

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