Author: Robert Hyatt
Date: 08:55:42 02/20/03
Go up one level in this thread
On February 20, 2003 at 09:36:24, Jeremiah Penery wrote: >Prime95 is a real-world application. It does very intense mathematical >calculation, testing several-million-digit numbers for primality. I don't >believe there's another program that will detect CPU problems faster. > The problem is that it won't detect _any_ floating point problems. Nor problems with unlikely instructions such as BSF/BSR, or fiddling with O/S issues like cache flushing, fiddling with the memory type and range registers, and so forth. There is a _lot_ of the chip that such an application simply doesn't touch, and when you use such a test to say "it works" it is like flipping a coin. If all you do is use the same instructions, you may well have a winner. But if you use something that your test didn't exercise, who knows? I don't have time for those kinds of random problems. If you do, that's certainly up to you to choose overclocking. >I overclocked my CPU for a while, and it appeared to be completely stable. I >could run Crafty for days with no problems, and I never had a crash or bug in >any other application. I ran Prime95 for a while, where a calculation error was >soon detected. Of course, when I clocked back to the normal level, the error >went away. Unfortunately your testing is backward. You assumed it was good because it ran without "crashing". But are you _sure_ crafty never computed a bad score? Or hosed the hash signature? Or generated a bogus move? No way to know. And if prime95 runs with no errors, are you _sure_ all the floating point stuff works? MMX stuff works? Oddball things like bsf/bsr? That's the flaw in this... > >I was running at somewhere near the maximum rated speed for that particular >core, which had about zero headroom to begin with, so the errors weren't all >that surprising to me. Had I bought a slower chip, I could have overclocked it >to the speed of my current chip very safely, as the core obviously has the >ability to run at that speed. Overclocking becomes particularly unsafe when one >tries to run at a speed above the normal ability of the core. Otherwise, it's >not much more than what the manufacturers do by taking chips from the same >silicon wafer and splitting them into different CPU speed bins, as those chips >should be theoretically _identical_. Note that we are not talking about buying 2.0ghz xeons and overclocking to 2.4. We are talking about buying the fastest chips made and overclocking _those_. That is a completely different issue, and that is what is being done in the cases being discussed...
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