[ntp:questions] Slow convergence of NTP with GPS/PPS
Richard B. Gilbert
rgilbert88 at comcast.net
Wed Oct 22 20:32:40 UTC 2008
David Woolley wrote:
> 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.
And it probably varies in frequency with temperature and age. And
probably no one cares if the frequency is off by a percent or two,
especially if it's off on the high side. Who is going to complain if
his 2.4 GHz processor is actually operating at 2.45 GHZ??
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