Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!cornell!batcomputer!itsgw!steinmetz!davidsen
From: davidsen@steinmetz.ge.com (William E. Davidsen Jr)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Computer Products United 386 16MHz
Keywords: Chapter Two.
Message-ID: <13345@steinmetz.ge.com>
Date: 10 Mar 89 23:13:11 GMT
References: <9804@ihlpb.ATT.COM> <10866@pasteur.Berkeley.EDU>
Reply-To: davidsen@crdos1.UUCP (bill davidsen)
Organization: General Electric CRD, Schenectady, NY
Lines: 57

In article <10866@pasteur.Berkeley.EDU> jsilva@cogsci.berkeley.edu.UUCP (John Silva) writes:

| A 16Mhz 386 can be successfully used at 20Mhz, *as long as they are kept cool*.
| The reason for this is the chip will generate a certain amount of heat in
| normal operation (which the specs account for), and running them at a higher
| clock rate will generate excessive amounts of heat.  This reduces the life
| of the processor, and the operating temperature range.
| 
| Generally, if you buy a 20Mhz 386 board with a 20Mhz processor you'll be paying
| a little more for increased lifetime and reliability.  Running a 386 out of
| spec isn't worth the hassle over the long run.

  You may have a good conclusion, but I think you got there using
incorrect information...

  Everything I have read or seen indicates that Intel does not have
assembly lines producing 386s in 20, and 16 MHz, but that there is
one chip foundry which produces 386s using the same parts and masks.

  Chips labeled as 20 MHz are tested at that speed and are guaranteed
for it. Chips labeled for lower speeds may be either (a) chips not
tested at the higher speed, or (b) chips which failed the higher speed
and passed the labeled speed.

  Intel says that they test under conditions which can not be duplicated
casually, using extremes of rated voltage and temperature. Just trying
it at home doesn't duplicate this. Therefore I agree that going with a
tested chip for peace of mind is a good idea.

  The chip does not change by putting a label on top which says 16 MHz.
There is no reason to suspect that a chip rated at any speed will run
hotter than a chip rated a any other speed. I therefore disagree that
running a slow chip at a high speed will "reduce the life of the
processor" more than running a fast chip. They should run at the same
temperature and have the same mean time to failure.

  This doesn't mean that the chip won't run hotter at higher speeds, not
does it imply that some chips may not run the higher speeds if they get
hot. Again you have the right idea, the chips may not be reliable if run
fast, but not because they run hotter than "fast" chips, just that they
won't run at the higher temperature.

  Depending on who you talk to, there is a 50-80% chance that any chip
which works at all will work at 20 MHz. If I had a system which I could
increase to 20MHz, I'd try it for any non-critical application.

  I think we've gotten to the same point from different directions.

NOTE: I don't have information on the 25 MHz parts for sure, but since
they are they same 'D' stepping using the same design rules you may
conclude that it's worth trying. Keeping *any* CPU cool is a good idea,
regardless of it's rating for speed or temperature. Remember "a cool
electron is a happy electron."
-- 
	bill davidsen		(wedu@ge-crd.arpa)
  {uunet | philabs}!steinmetz!crdos1!davidsen
"Stupidity, like virtue, is its own reward" -me