Path: utzoo!mnetor!uunet!vsi!friedl
From: friedl@vsi.UUCP (Stephen J. Friedl)
Newsgroups: comp.sys.ibm.pc
Subject: caution when cranking up the CPU clock
Message-ID: <49@vsi.UUCP>
Date: 26 Feb 88 01:17:07 GMT
Distribution: comp
Organization: V-Systems, Inc. -- Santa Ana, CA
Lines: 54
Keywords: 80x86, Intel, many MHz


     The following is from Jerry Pournelle's column in _Byte_,
March 1988 (page 183).  It is reproduced without permission.

[begin article]

"FAIR WARNING

     "Every now and again I see computers -- usually offshore-
constructed clones -- run at amazing speds, but when I look in-
side, the critical parts are ordinary chips.  'We select the good
ones,' one exhibitor told me at COMDEX.  'Try a lot until we find
parts that work.'

     "That sounds right, but it isn't, at least not in the case
of Intel chips.  I've been talking to a former Intel designer,
and he tells me that Intel has very elaborate test equipment.

     "When Intel makes a batch of expensive parts -- say, 386 or
387 chips -- they're put into the automated test setup and run at
the highest possible speed.  Most of them fail those tests; the
few that pass are then certified for that speed and sold at a
premium.

    "The rest of the parts are tested at lower speeds.  Those
that pass get certified; the others are tested at still lower
speeds and become the 'ordinary' stock.  A few don't pass at even
the minimum speed and are discarded.

     "The point is, every 'ordinary' chip Intel sells has *failed
a test* [Jerry's emphasis] at higher speeds.  That's guaranteed.
The failure the part experienced may not be critical.  Intel has
excellent test equipment and can find failures that may never
show up in ordinary use -- but could could you know what the
failure was?  It might be in a little-used area, but even
little-used features might be critical [like the early 80386 mul-
tiply? :-) SJF].  So while it's fun to crank up the speed on your
system, it's guaranteed that if you run Intel parts much above
their certified speed, you'll get failures.  Murphy's law will
take care of the rest."

[end of article]

     Please, no flames (about Intel QC or Jerry Pournelle).  This
was interesting and I thought it would be relevant for the many
netlanders looking at faster machines.  The above advice undoubt-
edly applies for all parts in your machine: look under the hood
before you buy!

     Steve
-- 
Life : Stephen J. Friedl @ V-Systems Inc/Santa Ana, CA     *Hi Mom*
CSNet: friedl%vsi.uucp@kent.edu  ARPA: friedl%vsi.uucp@uunet.uu.net
uucp : {kentvax, uunet, attmail, ihnp4!amdcad!uport}!vsi!friedl