From: eugene.leitl@lrz.uni-muenchen.de
Date: Thu Jul 15 1999 - 15:15:21 MDT
From: Christoph Wasshuber <wasshub@spdc.ti.com>
Let me put my two cents in this overclocking discussion.
Since I am working in silicon technology R&D I can give
you some insights from the fab. TI is not manufacturing
standard CPUs but we do quite good with fast DSPs, so
the experience should apply in general.
Overclocking will reduce the lifetime of your processor.
But since the lifetime of CMOS is very hard to control
precisely, that might be or might not be a problem. It is
very difficult because it changes from lot to
lot, meaning if you buy two processors at the same day
from the same distributor or vendor you might get two
totally differently behaving chips, with respect to lifetime.
The minimum lifetime of CMOS is somewhere around 10 years.
At least that is the target of manufacturing. But again that
is a statistical value, so most of the shipped chips do much better.
That means that even heavy overclocking should not realy
matter over the usual lifetime of a PC.
Going to finer and finer structures 0.18um, 0.13um means
that the production facilities are stressed to their
limits. Which means that variations become larger because
smaller transistors mean also more sensitivity to minor
process changes. Chips will have larger
variations than in the past. So you can end up with a much
better performing CPU than the specs tell you.
Stability is another issue. The best would be to write a program
which tests all possible signal combinations in the critical parts
of a processor. Running an application, no matter how
difficult it appears, is not a reliable general test. Of course,
if all you do is run one application it is enough to see if this
application runs stable. However, it is enough for one line of
assembly code to change, to let the CPU produce errors. Todays
CPUs are pretty sofisticated. So a simple black box test is
not reliable as a general test.
Nevertheless, I think overclocking is a smart way to get more
for less.
Chris....
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