How does the Motherboard's FSB affect CPU speed?

[redfella]

Hello,

I am under the impression that my CPU speed is directly affected by my mobo's FSB speed. At the moment I have a 533FSB mobo w/ a 800FSB CPU, if I upgrade to a 800FSB mobo will I see a noticable difference? My bios makes it sound like I cannot get the full potential of my cpu (only 1.8 worth out of 2.4 at the moment) if I do not have both the cpu and mobo at 800 FSB, is this correct?

Stats:

- Intel 2.4 800FSB Northwood CPU
- Asus p4s8x-x 533FSB mobo
- 1 gig Corsair XMS
- nVidia 128mb 6800
- yadda yadda

Thanks in advance.

 

[the cobbler]

I would imagine in an Intel you would see a huge difference in performance, because the FSB is what is "bottlenecked" in Intel's architecture.

please someone correct me if that assumption is wrong

 

[furballi]

NO if the core speed of the CPU is still the same.

 

[redfella]

Originally posted by: furballi
NO if the core speed of the CPU is still the same.

I have a 2.4 CPU, but my bios says its running at 1.8... This due to the 533 FSB mobo bottlenecking my 800 FSB CPU. What am at a loss still is knowing whether or not upgrading to an 800FSB mobo will help or not. As its stands its about 50/50. Half of everyone ive talked to says that it will help, the other half say the exact opposite.

 

[potato28]

Originally posted by: furballi
NO if the core speed of the CPU is still the same.

Wrong. The FSB will make it run faster, making a 2.4ghz cpu feel like a 2.4ghz cpu, instead of BIOS downclocking it to make it saturate the FSB.

 

[Fern]

Originally posted by: furballi
NO if the core speed of the CPU is still the same.

No, core speed is a function of FSB x Multiplier.

The multi on Intel's CPUs are locked. Meaning he can't increase the multi to compensate for a lower FSB.

In effect, his CPU is now underclocked.

Fern

EDIT: I don't see how your getting the CPU up to 1.8ghz on a mobo with 533mhz FSB speed. Here's the math:

Should be - 200mhz (FSB) X 12 (multi)= 2.4ghz CPU
As is - 133mhz (FSB) X 12 (multi)= 1.6ghz

Note: Intel mutliplies (marketing BS) their actual FSB speeds by a factor of "4". So, a 533mhz FSB is actually 133mhz (533 divided by 4). 800 FSB is actually 200 (800 divided by 4).

Have you OC'd the mobo (raised the FSB)?

Is your Corsair ram PC3200 (or DDR400, whichever way you like to say it )

 

[kmmatney]

As said above, you are underclocking the cpu. The cpu is running at 1.8 GHz instead of 2.4 GHz. You may be able to get some more performance if you overclock the FSB as high as you can, but it looks like you need to get a new motherboard with 800 MHz FSB.

 

[redfella]

Originally posted by: Fern
EDIT: I don't see how your getting the CPU up to 1.8ghz on a mobo with 533mhz FSB speed. Here's the math:

Should be - 200mhz (FSB) X 12 (multi)= 2.4ghz CPU
As is - 133mhz (FSB) X 12 (multi)= 1.6ghz

You are exactly right, I'm not even getting 1.8ghz... only 1.6ghz!

Thanks everyone, this is exactly what I needed to hear. I was orginally under the impression that getting a new motherboard would help significantly, but a couple people said otherwise... However, now I'm positive getting a new mobo will help a lot. Thanks again.