Path: utzoo!attcan!uunet!crdgw1!sixhub!davidsen From: davidsen@sixhub.UUCP (Wm E. Davidsen Jr) Newsgroups: comp.sys.ibm.pc.hardware Subject: Re: 386sx Motherboard Message-ID: <2045@sixhub.UUCP> Date: 7 Oct 90 17:00:39 GMT References: <1990Oct3.173937.995@urz.unibas.ch> <1990Oct4.141439.1039@eng.umd.edu> Reply-To: davidsen@sixhub.UUCP (bill davidsen) Organization: *IX Public Access UNIX, Schenectady NY Lines: 46 Okay, let me see if I can clarify this, since a lot of people are posting parts of the answer. When chip are available in several sppeds, there are two cases: (1) the chips are a diferent process, or (2) the faster chips are selected from the same line as the slower. If the chips are case (1), using a slower part is a bad idea for two reasons, it is very unlikely to work reliably, and it may overheat. As the clock speed goes up the power disipation goes up (not linearly) due to driving the internal capacitance (and some other stuff). Damage to the chip is unlikely, but as it gets hotter it changes some internal timings, and it may not give correct answers. If the chips are case (2), the manufacturer will test all chips at the higher speed and label the ones that pass FAST (whatever that means for that chip). Then the ones which fail are tested at the slower speed, and if they pass they are labeled SLOW, or they are not labeled at all. However, as the type (2) process improves, the line will produce more FAST chips than are needed. Therefore chips in excess of demand are only tested SLOW. When using a 16MHz chip at 20MHz, you may be using - a chip of another process, not designed for the speed - a chip which failed at the higher speed - a chip not tested at the higher speed * which is okay * which would fail is tested FAST I have regularly pushed 16MHz 386DX parts to 20MHz, and 286 from 6->8 MHz. In the case of the 386SX, I believe that the 20MHz part is another process, and it is not a good idea, although Intel was getting their 20MHz parts by picking the 16 (I'm told) for a while, and while the yield was not good, the parts didn't run overly hot. Note that I have not told you what to do, but at least this may clear the air. You really have to know if the situation is type (1) or (2), then make the decision. This is why the spole saying "don't ever do it" and "that's how Intel does it" are both partially right. -- bill davidsen - davidsen@sixhub.uucp (uunet!crdgw1!sixhub!davidsen) sysop *IX BBS and Public Access UNIX moderator of comp.binaries.ibm.pc and 80386 mailing list "Stupidity, like virtue, is its own reward" -me