[Beowulf] ...Re: Benchmark results

[Josip Loncaric]

Jim Lux wrote:
> 
> We're talking parts per million here, though, just to keep things in 
> perspective.

I just checked some quartz crystal oscillator specs, and they range all 
over the place.  The cheap ones recommended for Gigabit Ethernet devices 
claim 100 ppm stability, but good quality ones can be ordered with 0.1 
ppm specs.

HP application node 200-2 "Fundamentals of Quartz Oscillators" (see 
http://www.measurement.tm.agilent.com/main.cgi?PSP_NEXT=Redirect&Document:CONTENT_ID=6980) 
says that temperature effects are the dominant influence (2.5 ppm within 
0-50 deg. C).  This is followed by aging (<0.3ppm/month), line voltage 
change (<0.1ppm/10% change), and various other smaller effects.

A good crystal may deliver <2.5 ppm frequency variation over a 0 to 50 
deg. C range, but the temperature dependence may be quite nonlinear. 
Temperature compensated crystals can deliver 0.5 ppm stability over the 
same range.

Sincerely,
Josip

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