"John Manning" said:
I can't afford to upgrade the motherboard and CPU at the same time, so I
would like to run an 800MHz FSB Northwood P4 in an Asus P4B533-E. I know
that the CPU will be underclocked in this case but will it still work until
I can buy a motherboard that supports an 800MHz FSB?
Has anyone tried something like this?
TIA,
John
If you look on this page:
http://www.asus.com.tw/support/cpusupport/cpusupport.aspx
you can see what processors are supported. You can see there is
one P4 with a 256KB cache, and that could be a Willemette. The
rest appear to be Northwood based. There are no Prescotts listed
on the page, so I wouldn't try one of those (the Vcore a Prescott
needs, might not be available or coded properly for your
motherboard).
Another interesting thing on that page, is the 3.06GHz/533 processor
requires a revision 1.02 motherboard. That is likely just to get
Hyperthreading support. If you don't have revision 1.02 or later
motherboard, then you likely won't get Hyperthreading to work
(no big loss).
Another issue can be power consumption. What I would do, is look
up the data for a 3.06GHz/533 processor, see how much current it
draws, then compare to the current your FSB800 processor draws.
The 3.06Ghz draws 65.4 amps at roughly 1.5V . The amperage is the
most important factor, as the amps cause heating of the MOSFETs,
and at some level, saturation of the powdered iron toroids.
The 3.0Ghz/FSB800/512KB Northwood draws 64.8 amps at again,
roughly 1.5V , so even if it could be run at full speed, there
is sufficient current. Since power is proportion to FCV**2, the
reduction in F would lead to a directly proportional reduction in
power - the current drawn will be roughly reduced by a factor
533/800. So, you are well covered there.
ftp://download.intel.com/design/Pentium4/datashts/29864312.pdf
Next comes the BIOS. Asus BIOS try to ascertain various amounts
of information about a processor. On an AMD board, there is some
kind of profile used, and so the BIOS likes to match the processor
it finds, to that profile. (Without more info on chipsets and
the like, it is pretty hard to determine exactly what is being
"tuned" in the profile.) On the Intel side, many of the most
recent processors have had certain features added (EIST speed
step, EMT64 extension, PRB for Prescott 4A/4B power type), which
while not necessarily failing to post completely, may lead to
not getting full performance.
That being said, a FSB800 Northwood likely doesn't have that
much different a multiplier. Say we compare a 2.53/533 to a
3.0/800, the 2.53 would be 133 x 19, and the 3.00 would be
200 x 15. Running the 3.00 at 133 x 15 gives 2Ghz as your speed.
The only thing that will likely go missing, is the microcode
loader. A 3.06/533 processor will have a different family code
than a 3.0/800 processor, and you may see a BIOS warning about
the missing code. WinXP and perhaps WinXP SP1 will likely load
the required microcode for you, leaving the boot interval as
the longest period the processor will be run without the
proper microcode patches. (SP2 will likely fall on its face,
if you don't fix the microcode
))
New microcode can be added to an old BIOS, as long as CTMC
can be used to add the code. It really depends on whether your
BIOS is Award or AMI, as CTMC only works with an Award BIOS.
(See page 311 section 8.10.4 for info on INT 15h 0xD042 call.)
http://www.intel.com/design/pentiumii/manuals/24319202.pdf
I would say the odds are excellent, of being able to run the
Northwood. Jamming a CeleronD (Prescott core) in there should
yield a black screen. Putting a Prescott FSB800 in there, I
have no idea what might happen - the results could be a little
more positive than the CeleronD experience, but there is more
potential for a black screen with that choice as well.
I say with the Northwood, "go for it"
Do some Googling on CTMC and microcode,
to find out how to extract a 2KB microcode segment for your
new processor, from another motherboard's downloadable BIOS
file, and then add it to your board. The CTMC method has the
advantage that it doesn't endanger the BIOS like trying to hack
a completely new BIOS file. CTMC uses a BIOS hook, to write
the microcode to a 2KB location reserved in the flash ROM for
it, and the rest of the BIOS code is untouched. Since the 2KB
location is "volatile", you may have to repeat the CTMC update,
if you change processor types a lot on the board. The BIOS
warning will tell you, if the 2KB segment ever gets overwritten
by some other microcode.
Post back how it works out.
HTH,
Paul
