[ntp:questions] 500ppm - is it too small?

David J Taylor david-taylor at blueyonder.not-this-bit.nor-this.co.uk.invalid
Thu Nov 12 16:49:01 UTC 2009

"Ulrich Windl" <Ulrich.Windl at RZ.Uni-Regensburg.DE> wrote in message 
news:874op0szuz.fsf at pc9454.klinik.uni-regensburg.de...
> "David J Taylor"
> <david-taylor at blueyonder.not-this-part.nor-this.co.uk.invalid> writes:
> [...]
>> Ulrich,
>> So machine running other than Windows don't suspend?  In any case, it 
>> was more
>> the clock-speed variation I was thinking of.
>> But I note that you think 500ppm is enough.
> [Skipping the part where you are saying I'm insulting]

It must have come across that way, but if not intended, then no offense 

> Yes, as even most mechanical wrist-watches are better than the 500PPM
> that NTP allows, I'm really getting tired of people trying to fix the
> broken hardware clock with software, just because the hardware vendor
> saved a few cents on the crystal. Also, NTP (and possibly operating
> system's time routines as well) was never designed for
> machines that use variable clock frequencies. So I assume: If you really
> care about a clock that is closer than 100ms to the real time, you'd use
> the proper hardware with NTP. Otherwise use something else.

You've hit one nail on the head with variable clock speed.  I think that's 
now a fact of life with today's processors and view of energy consumption.

> IMHO, most people don't care if their clock is a few minutes off, but
> with using NTP they suddenly expect that their clock will automagically
> become as good as an atomic clock.
> Ulrich

With two or three PCs here speaking the time, syncing to within a few 
milliseconds would be nice.  We do also have one application where needing 
to know the time to within a few seconds is critical, and we are trying to 
use NTP for that on a whole mass of individual users' PCs.


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