The system I built/overclocked is a Pentium-II 266 with a Shuttle
Computer International HOT-641 motherboard and 256 megs of 10ns RAM.
The original bus clock speed was 66 mhz which I upped to 83 mhz in the
BIOS Configuration Utility. I had to remove the case and train a 3"
desk fan on the CPU to keep it cool enough to run at 333 mhz but the 20%
increase in speed was worth it. I ran a burn-in test on it for 2 solid
days when I first overclocked it to make sure I didn't have a weak
processor, and when I started Prime95 I tortured it for about a half of
a day with no errors so I figured it was good to go. I think the
problem is heat-related, due to the onset of hotter months in this
climate and the poor ability of our air conditioner to handle the heat.
I have since started looking at P2-450mhz processors because adding an
extra 20% to the Prime # "expected completion date" test time after
having a shorter completion time is rather irksome.
Thanks to all the list members who offered different and vaild
viewpoints as to the nature of the problem. I have since configured my
reported CPU speed in Prime95 back to 266 (which I forgot to do), and
the reported time between iterations increased to a more accurate
figure.
Gary Diehl
Brian J Beesley wrote:
>
>
> > It is also possible to have an overclocked CPU pass the full self test
> > suite, but later exhibit problems. The likely culprit is simple wearout
--
> > the CPU initially was barely functional at the overclocked speed, but slowed
> > enough that it no longer runs. If this happens, you usually can still run
> > the CPU at the rated speed.
>
> Or, the errors are there all the time but at a low rate e.g. on
> average 1 every day. This is very likely to pass the 1 hour "self
> test" but will show up in actual use, or on the continuous "torture
> test" (see the "Options" menu in Prime95).
>
> If you've overclocked your system at all (_not_ reccomended, but I
> know it can be successful in some cases) then I suggest you let
> the torture test run for a couple of days before committing yourself
> to doing "real" work. It can happen that an overclocked system
> appears to run fine for "office" applications but causes problems
> with Prime95 because very few other applications use the floating-
> point unit even half as intensively as Prime95 does.
>
> Note that simple overheating can also cause problems, even if your
> system _isn't_ overclocked. Might be an idea to check that case
> and processor cooling fans are operating. They have been known to
> fail!
>
> Finally (I think this is right - I'm sure George will chip in if not) there
> is a small but finite chance that you could get a very occasional
> "sum out error" even if your system is 100% perfect. This is due to
> abnormal combinations of data in the FFT triggering the "sanity
> check" in the code; the result may well be OK. The program should
> check that the "error" is "deterministic" (repeatable) rather than
> random and continue automatically if it is - though there will be an
> error log entry - PrimeNet uses this information to flag the result as
> "suspect", the exponent should then be re-assigned for an early
> double-check instead of waiting its turn as usual.
>
> Regards
> Brian Beesley
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