533FSB CPU on a P4B?

[Erwin]

I just got a P4B rev 1.05 cheap, and I'm thinking about using it to
upgrade my P2B system (which already has PC133 RAM). So all I need is a
new CPU, preferably a P4 2.4GHz, but I want to know at what FSB.

The reason I'm not sure is that the Asus website and documentation for
this model state that it will only support 400FSB CPU's. But the
jumpers also clearly sport a 133MHz (533FSB) for CPU setting!

So what is the deal? Didn't 533 CPU's exists yet when the P4B was
introduced and is it only "officially" unsupported, or will 533 CPU's
not run on a P4B at all?

And what BIOS version should I load? 1012 or 1014 beta 3?

-- Erwin Dokter

 

[Paul]

I just got a P4B rev 1.05 cheap, and I'm thinking about using it to
upgrade my P2B system (which already has PC133 RAM). So all I need is a
new CPU, preferably a P4 2.4GHz, but I want to know at what FSB.

The reason I'm not sure is that the Asus website and documentation for
this model state that it will only support 400FSB CPU's. But the
jumpers also clearly sport a 133MHz (533FSB) for CPU setting!

So what is the deal? Didn't 533 CPU's exists yet when the P4B was
introduced and is it only "officially" unsupported, or will 533 CPU's
not run on a P4B at all?

And what BIOS version should I load? 1012 or 1014 beta 3?

-- Erwin Dokter

The original 845 Northbridge datasheet only refers to BCLK=100MHz.
But since the Northbridge doesn't actually have a spec for
maximum BCLK clocking rate, there is no way to know whether Intel
intended faster operation or not. Intel is a pretty conservative
company.

Since the motherboard is from the Northwood era (0.13u), no matter
whether you select a FSB400 or a FSB533 processor, you should use
a Northwood processor. The BIOS is not likely to work with a
CeleronD or a Prescott P4 processor (90nm). (Other boards "black
screened" with the CeleronD, and there is no reason to expect this
board to be any different.)

The board is overclockable, and if you can find a Northwood with
a FSB533 bus on it, then I think it is worth a try. It is likely
you'll find more FSB400 processors around. So, the market may
have more to say about what processor you get, than the motherboard.

http://groups.google.ca/[email protected]

Paul

 

[Erwin]

Heh, not only can you jumper the FSB to 133MHz, in jumperless mode, the
FSB can be set all the way up to 200(!)MHz! The CPU won't be the
problem, I just want to know if the 845 can cope with 133.

Then again, would it improve performance since the memory is only
running at 133MHz? I don't think the FSB would be the bottleneck here.
I'd rather buy the 533 version so I can move it to a future board.

-- Erwin Dokter

 

[Paul]

Heh, not only can you jumper the FSB to 133MHz, in jumperless mode, the
FSB can be set all the way up to 200(!)MHz! The CPU won't be the
problem, I just want to know if the 845 can cope with 133.

Then again, would it improve performance since the memory is only
running at 133MHz? I don't think the FSB would be the bottleneck here.
I'd rather buy the 533 version so I can move it to a future board.

-- Erwin Dokter

For performance, "clock rate is king".

Performance improves if the core clock can be increased.
Performance improves if the memory clock can be increased.

The core clock is the most sensitive adjustment. Memory less so.
A 30% improvement in memory bandwidth gives a 10% improvement
in application performance (broad sweeping statement for
average usage patterns - not true for Photoshop).

That being said, switch from a 1.8GHz FSB400 with PC133 to
a 2.4Ghz FSB533 with PC133, will give exactly 33% more
performance when using a compute bound application. If you
were doing Photoshop, for example, the disk drive and the
memory will have a lot more to say about the matter, so the
improvement will not be 33%, but there will still be a
little improvement.

At FSB400, the bus transfer rate is 3.2GB/sec. A single
channel bus with PC133 memory on it, transfers at
133*8=1064MB/sec. Neither FSB speed you are looking at, is
seriously stressed talking to SDRAM memory, so the FSB is
relatively unimportant. The 845 can run memory faster than
133MHz, as I've run three sticks at 146MHz (I didn't test
with Prime95 for stability, but it did boot with no problem.)

The datasheet for the 845 says BCLK=100MHz, but I believe
(based on comments at the time) that 133MHz should be no problem,
and perhaps up to 160MHz is possible if you own really
good ram (some of the PC150/PC166 for example). When I purchased
my P4B, my plan was to overclock my 1.8A to 2.4GHz, and that
was based on comments that it was a virtually guaranteed
overclock. I would think a Northwood 0.13u FSB533 processor
would be no problem at all.

HTH,
Paul