CPU upgrade question

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I'm putting together an upgrade for a friend.  He has a P4T533-C, which
supports hyperthreading but only has a 533 MHz bus speed.  My question is,
will a CPU with an 800 MHz capability work in this MB?  Will it just run
slower than it's capable of?

I realize that there is a 512K cache limit with this MB.  I already ran into
a problem with that, trying to install a Prescott CPU with a 1M cache.  Now
I have an extra CPU on my hands.  I don't want to make any more blunders.
:^(   TIA.

Tom S

Re: CPU upgrade question

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I'm curious how you came to the conclusion it was the cache
that broke it. Do you realize there is an extra signal on the
Prescott called BOOTSELECT ? On an old motherboard, the pin
of the socket, that corresponds to that signal, is grounded.
Basically, the scheme allows a newer processor, to tell it
is being plugged into an older motherboard. The processor
stopped that experiment from working, not the motherboard.
(I have no idea what happens if you snap that pin off on
that Prescott you've got :-) You could be a first. Or you
could be a proud owner of a dead socket 477 processor. )


Intel may have done that, to prevent a higher power consuming
processor, from damaging the Vcore regulator on an older
motherboard. Each generation of processor gets a slightly
different VRM or VRD (vcore regulator) spec. (And of course,
Intel now has a policy of "make'em upgrade", so this should
not come as a surprise. Intel wants you to buy all new gear,
and keep the computing industry healthy :-) )

So, assuming your board grounds BOOTSELECT, at the very least,
you would want to download datasheets for processors, until you
find a generation of processor that doesn't have such "defense
mechanisms". The answer will likely be a 0.13u Northwood.

Or, you could use the supported processor list here:


The fastest approved processor is 3.06GHz/FSB533/512KB L2, which
is a Northwood. If you cannot find one anywhere else, Powerleap
has one for $269 on this page:


Now, let us assume you could find an imaginary Northwood processor.
Say there was a 3.8GHz/FSB800/512KB L2 processor available.
If you run that at FSB533, the multiplier is locked, and
the processor runs at (533/800)*3.8 = 2.53GHz, which is slower
than the 3.06GHz mentioned above. If you overclock the FSB a bit,
to say FSB640, now you have achieved exactly what you could have
by using the $269 processor from Powerleap, except you would have
paid a small fortune for the FSB800 Northwood. And I doubt there
is such a thing as a 3.8GHz Northwood.

So, stick with the plan as laid out in the CPUSupport page.
Much less hassle and research work to do.


Re: CPU upgrade question

Thanks for the tips, guys.  Good info.

Tom S

Re: CPU upgrade question

No.  It will not run.


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