Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!milano!bigtex!james From: james@bigtex.cactus.org (James Van Artsdalen) Newsgroups: comp.sys.ibm.pc.hardware Subject: Re: Physics of chip Failure (was Re: 386sx Motherboard) Message-ID: <48380@bigtex.cactus.org> Date: 5 Oct 90 21:35:07 GMT References: <1990Oct4.141439.1039@eng.umd.edu> <48351@bigtex.cactus.org> <1990Oct5.171736.13039@eng.umd.edu> Reply-To: james@bigtex.cactus.org (James Van Artsdalen) Organization: Institute of Applied Cosmology, Austin TX Lines: 24 In <1990Oct5.171736.13039@eng.umd.edu>, dank@eng.umd.edu (Daniel R. Kuespert) wrote: > While the dangers of pushing chips beyond their design speeds seems to > be well known, I've never been sure exactly _why_ they fail. My > original post (the "While you might get lucky..." above) focused on > overheating. [...] Heating slows down the signal paths in a chip because the resistance is increased. For PCs, the most important factor is likely to be that the signals simply take X nanoseconds to traverse the logic in the chip and to be driven on the pins. It doesn't matter how fast the clock goes, it still takes X ns to do the work. Speeding up the clock makes it possible to use a smaller X better, but it doesn't change X. As a chip heats up, X usually becomes longer, which is why a 386 with a "fast" crystal might work for a little bit and then fail hard. I don't know if the most likely failures will be internal signal paths, or external signal timing. Probably, "depends"... -- James R. Van Artsdalen james@bigtex.cactus.org "Live Free or Die" Dell Computer Co 9505 Arboretum Blvd Austin TX 78759 512-338-8789