[time-nuts] Selecting server hardware (newbie question)
Hal Murray
hmurray at suespammers.org
Tue Jan 31 04:32:33 EST 2006
phk at phk.freebsd.dk said:
>>Most systems use the 32 KHz battery backed TOY (Time-of-Year) clock
>> for timekeeping rather than the CPU crystal.
> Wrong, few systems do. Most systems use the 32.768 kHz xtal to run
> their battery-backed Real Time Clock, but this is only consulted on
> boot to get an initial fix on time.
Thanks for the heads up.
>>This is good because it's generally farther from the heat
>> generating CPU than the CPU crystal.
> This has no hold in reality.
It's not what I was expecting. Several years ago, I was trying to match the
temperature of the crystal with the observed drift. The data looked a lot
better after Dave Mills pointed out that I was measuring the temperature of
the wrong crystal.
http://www.megapathdsl.net/~hmurray/ntp/drift.gif
http://www.megapathdsl.net/~hmurray/ntp/drift-ex.gif
I think he said it was done that way in order to support SMP systems. I'm
pretty sure it works that way on this old Linux box. I probably jumped to
the conclusion that it was more common than it is.
Anybody got a list of which systems use which crystal?
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