Does the CPU care about FSB???

[Terminator]

I raise this question because with all the clocking we do I was curious when they 'create' a CPU is it designed for a specific market area?. When clocking it seems we can clock whatever chip by bumping the FSB (locking the PCI etc for stability) to whatever!!! Multipliers always seem to be the problem.

So the question really is.... Say for instance we have a 200MHz FSB AMD.... is there a limit??? Or similarly for Intel chips..

I'm assuming we have memory that would support any 'reasonable' speed.

T

[Midknyte]

I'm not sure what you are asking. The CPU will have a certain overall clock tolerance. If you reduce the multiplier, you can theoretically increase the fsb until you hit the CPU's overall clockspeed max. other things like chipset and memory come into play also, but generally a faster fsb is better.

[causticVapor]

Some CPUs actually have a limit that the FSB will tolerably run at. I remember AMD making a tbred stepping revision so its FSB interface would be able to interface more quickly with the northbridge (tolerate higher FSB speeds). This lead to Barton's 166MHz bus.

[Terminator]

Cheers causticVapor

That's what I wanted to know.

My question originally was to ask the question 'is a CPU designed for a SPECIFIC FSB or for an overall MHZ speed.

This is because we seem to run ..eg. XP2500's at 10X200 no prob...and it will run at 12*166.. similar overall MHz.


So they DO design CPU for a specific FSB and us bad lads run them out of spec.

T

[causticVapor]

Well, theoretically a CPU can run with an FSB the same speed of the processor or greater, but that would cause a lot of noise problems on the traces connecting the CPU to the northbridge and/or memory. It's simply impossible to go that far that fast without a redesign of the traces on the FSB.

[Midknyte]

The chipset is more sensitive to FSB than the CPU. Look at the new P4EE with 1066 FSB versus 800FSB. They both run at the same overall clockspeed, however the motherboards they run on are different (925XE versus 925/915/875/856)

[causticVapor]

Well in the scenario I was assuming a northbridge that could keep up with the CPU. Pretty hard to do, yes, but it was the constant in my example.