Newbie Help

[bruce.gettel]

Hi,

Can I run a processor with an 800MHz fsb on a mobo that only supports
533MHz fsb?

Thanks.

 

[peter]

maybe....but not at 800
if your present CPU is running 8x266(Double Data Rate brings it to 533) then
it is running at 2.128
if the new processor runs at 8x400 that would make it a 3.2 but since you
cannot go higher than 533 it would only run at the same speed as the old.
Then there is the Socket type.........
then there is the power requirements
then there is the mobo............
then there is Overclocking.........

peter

 

[Paul]

Hi,

Can I run a processor with an 800MHz fsb on a mobo that only supports
533MHz fsb?

Thanks.

The interface is the same. The difference is in what happens when
the BSEL pins are presented to the motherboard.

If a motherboard is built the way that Intel would like, the BSEL
pins would go directly to the clock generator chip. Then, for the
processor to work, the clock generator chip has to have a setting
that corresponds to the BSEL value. For a FSB533 processor, the
BSEL tells the clock gen to make 133MHz. A different BSEL value
is delivered by an FSB800 processor, and that tells the clock gen to
make a 200MHz signal for the CPU input clock.

The question then is, how does the clock gen respond, when it sees
a BSEL that is not expected by design ? The clock gen could deliver
a clock even lower than the one you expect. (I.e. It could run your
processor at FSB400, and give half the expected performance. That
makes a truly pointless upgrade.)

The BIOS also plays a part. The BIOS loads microcode patches for
all the processors it knows about. That is not essential to making
the processor work (as WinXP also has a microcode loader to solve
such problems). But the BIOS could "play dumb" when it reads the
family ID of the new processor, and you could, in theory, get
stuck during the POST sequence. For example, many Asus BIOS will
not allow an unknown processor to POST, so there are no certainties
about things like this.

A question would be, what benefit do you get from this experiment ?

Let's take an example. You happen to find a 3.4GHz/FSB800 processor.
Say the motherboard runs it at FSB533. The final core speed is
(533/800) * 3.4GHz = 2.26GHz. Now, instead of that, you
could buy a 3.06GHz/FSB533/512KB L2 Northwood processor, and
it would run at 3.06GHz (because it has the right FSB).

Generally, it is better to match a high end proper processor
with your older motherboard, because it will give its true
speed. Using a FSB800 one, will likely result in the thing
slowing down, due to the motherboard running it at FSB533.

If you'd mentioned the motherboard maker and model number, or
if this is a Dell/HP/Gateway etc., the model number of the
computer, that makes it easier to look up and guess at the
hardware response.

Another thing to keep in mind - a FSB533 motherboard is from
the Northwood (0.13 micron) era, and not the Prescott (90
nanometer) era. If you insert a Prescott processor, the processor
will likely not POST, because a Prescott can detect when it
is plugged into an incompatible motherboard. Nothing bad
happens - the fans spin like they always did, but not even
one BIOS instruction gets executed. The Prescott processor has
a pin on it, that checks the kind of motherboard being used, and
the processor rejects the motherboard. So that is another
possible result. And a good reason to be checking the
CPUSupport web page of the motherboard, for any warnings
to that effect.

For that reason, if you are using a motherboard which is meant
for Northwood processors, better to search for one of those.
You can use processorfinder.intel.com to convert the OPN or the
SLxxx code, into technical specs. In that way, you can detect
whether the processor for sale is 0.13u or 90nm.

This is an example of a 3.06GHz/FSB533/512KB L2 Northwood processor.

http://processorfinder.intel.com/Details.aspx?ProcFam=0&sSpec=sl6pg&OrdCode=sl6pg

The best way to check out whether an upgrade makes sense, is to
see if someone has done it before you. That takes some of the
uncertainty out of it.

They list a 3.06GHz/FSB533/512KB, second one down on the right hand
column of this page. The advert says "Limited supply" so they
may finally be running out of them. You can certainly do better
on price, by shopping elsewhere. Being aware though, that places
like Ebay, may not provide as much identifying information about
what you are buying - for example, there is a Xeon 3.06GHz processor
too - so be careful you don't buy the wrong type.

http://www.powerleap.com/Processors.jsp

HTH,
Paul