>From: "Brian J. Beesley" <[EMAIL PROTECTED]> >To: "Nathan Russell" <[EMAIL PROTECTED]> >CC: [EMAIL PROTECTED] >Subject: Re: Mersenne: The sound of M(M(19)) >Date: Sun, 7 May 2000 08:58:21 -0000 > >Much more likely to be related to a resonance with the speed at which >the FFT works at the exponent you're testing. ECM will be on a small >exponent (memory requirements!) so the FFT will run very quickly >compared with the same code running on a larger exponent. My guess is >that if you run ECM on an exponent say 30% bigger, or smaller, the >noise will vanish. Unfortunately, AFAIK, there is no tracking on George's of curves being done on exponents very near M(M(19)), except for F(19), which is far too near to be different in terms of FFT size. Were this not the case, I would run a curve or two on a nearby exponent. > > > > In any event, though, I cannot help being somewhat curious about the >source > > of the sound. Does it relate to the writing to and from memory? > >Probably something loose (maybe inside the processor cartridge) is >excited by an oscillating electric field, causing mechanical >vibration, which can get large enough in amplitude to make itself >obvious by causing contact with a non-moving part if the loose >object's natural frequency is close enough to the frequency of the >driving field. Is this something to be concerned about? > >The cheap & nasty way in which Intel join the heat sink/fan unit into >the processor cartridge proper on their SECC2 processors (cartridge >slot PIIIs) seems to have the potential to resonate seriously. If >you're feeling brave, it would be possible to disassemble this & >refit the heatsink properly, eliminating mechanical sloppiness as >well as getting better thermal contact. Well, since this in only a brief (5-curve) run in between my regular work, I'm not going to worry too much until someone tells me that I need to. It's already on curve 3, so I think it will finish today. > >I doubt it's much to do with memory access; for exponents typical for >ECM tests, the transforms will run inside the processor's L2 cache, >maybe even in the L1 cache. Also, the memory loading for ECM is very >different between Stage 1 and Stage 2; if the noise is present during >both stages, we can pretty well rule out memory access as its cause. Duly ruled out. >There is still some memory access requirement - more in Stage 2 than >in Stage 1, but still a lot less than the demands of LL testing an >exponent well into 7 figures - but running ECM simply isn't dominated >by memory bus throttling in the same way that LL testing can be. Okay, I'm confused here. First you informed me that ECM on higher exponents was limited by memory requirements; now you tell me that the memory requirement is less than that of LL testing. M(M(19)) is a quarter of the size of the largest exponent (F(20)) that George regards as workable for memory reasons. Where is my understanding wrong? Puzzled, Nathan, hoping against hope that his message doesn't get caught in the loop as well. ________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com _________________________________________________________________ Unsubscribe & list info -- http://www.scruz.net/~luke/signup.htm Mersenne Prime FAQ -- http://www.tasam.com/~lrwiman/FAQ-mers
