Underclocking Pentium D 3.20 GHz (dual core, multi-threaded)

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Just wondering if anyone has any experience in underclocking this kind
of processor. Mine is unstable when using it for very complex
calculations (wouldn't mind it running a bit quieter too :)
I'm wary of making BIOS changes, as everything is set to AUTO and I'm
not sure of what voltage and speed settings are safe.
Any ideas, or know of any decent documentation on this?

Re: Underclocking Pentium D 3.20 GHz (dual core, multi-threaded)

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Doesn't it seem a bit silly to be doing it this way ?

There are a couple of tests you can run.

1) Get a copy of memtest86+ from memtest.org . There is a version
   that will format a test floppy diskette for you, and a second
   version that runs as a bootable CD. Allow the test to run for
   two passes. You are allowed _No_ errors. If errors are listed,
   you need to fix that first. A typical fix for memory errors,
   is to increase the DIMM voltage (Vdimm) a bit in the BIOS.
   If this is DDR, then raise the voltage from 2.5 to 2.7V for
   example. If DDR2, maybe a bump from 1.8V to 2.0V would help.

2) If the memory tests clean, now boot back into Windows (or
   Linux if you want). Go to mersenne.org and get a copy of
   Prime95. I haven't used Prime95 on a dual core machine,
   but there must be some way to run it on both cores at
   the same time. If you have a utility that will display
   the CPU temperature, run that utility at the same time.
   You are looking to see if the CPU temp stays below 70C
   wnen Prime95 is running on both cores. Modern processors
   have throttling, and if the temp passes 70C, the processor
   responds by reducing the internal compute rate. You should
   not see the temp pass 70C in any significant way, unless
   maybe the heatsink fell off. The computer will shut down,
   if the temp reaches 90-95C or so, on the latest processors
   (shutdown is about 20C above the throttle temp).

Prime95 will error out in a very short time, if your CPU or
memory are bad. If Prime95 "torture test" option will run
for hours on end, then the CPU and memory should be in
reasonably good shape.

Again, you can try bumping up the CPU voltage a bit, and
see if that helps. But chances are, if Prime won't run without
errors, it could be memory. For example, booting Linux and
testing with four copies of Prime95, I assigned each copy a
"chunk" of RAM. (In Linux, you can run multiple copies, by
simply making a test directory for each copy of the program.)
The same "chunk" of RAM failed after 30 minutes of testing,
which told me that the RAM was defective. If the errors were
processor related, then the errors would be randomly
distributed with respect to whichever chunk of memory was
being tested.

If you have good reason to believe that the processor is
actually defective (yes, it does happen some times), then
the processor is covered by a warranty. It would be
better to do a warranty return, then have to run the
thing de-clocked.

Improving your case cooling, will mean that the CPU fan
will not have to work as hard. There are some pretty
pitiful computer cases out there, designed by idiots.
For good airflow, there should be a defined direction for
the air to move. By convention, air enters at the front
of the computer (and if the cool room air flows over the
hard drive first, so much the better, as the hard drive is
the most temperature sensitive part of the computer).
Air exits at the back of the case. There should be large
fans, large inlet vent spaces, and no restrictions to airflow,
if you expect to keep the inside of the computer case cool.

It is possible to fix miserable computer cases. I've put a
modern motherboard in a crappy case, by fashioning a metal
frame that sits in front of three 5 1/4" drive bays on the
front of the computer. I positioned a big fan, blowing into
the computer case. The fresh room air blows over the hard
drives, which are still in the bays. The fan sits on the
outside of the computer case, as there would not be
room inside. To make ventilation space at the back, I
removed all the PCI slot covers which did not have PCI
cards in them. That turns a crappy case for cooling, into
a slightly less crappy case :-)


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