FSB Questions

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Tim

I have a few questions regarding the FSB and how it affects the CPU ...

1) Are FSB frequency pulses generated from within the CPU itself or from
somewhere else? Where is the oscillator (if that's what it's called), and
where is the multiplier?

2) Hypothetically, if you have a processor with a 1GHz speed rating, which
it achieves using 100 MHz FSB and a 10x multiplier, what happens when you
achieve that 1GHz using an overclocked FSB and a lower multiplier? Does it
put a strain on the CPU, even though the final CPU speed is still running at
its intended frequency?

Thanks in advance.
 
I have a few questions regarding the FSB and how it affects the CPU ...

1) Are FSB frequency pulses generated from within the CPU itself or from
somewhere else? Where is the oscillator (if that's what it's called), and
where is the multiplier?

2) Hypothetically, if you have a processor with a 1GHz speed rating, which
it achieves using 100 MHz FSB and a 10x multiplier, what happens when you
achieve that 1GHz using an overclocked FSB and a lower multiplier? Does it
put a strain on the CPU, even though the final CPU speed is still running at
its intended frequency?
Click to expand...
1) From a clock generator on the motherboard.
2) No but it does stress other components as depending on the
motherboard you're also overclocking the PCI/AGP and memory.
 
1) From a clock generator on the motherboard.
2) No but it does stress other components as depending on the
motherboard you're also overclocking the PCI/AGP and memory.
Click to expand...

Second half of number one . . . as the CPU must run at a speed much higher
than most motherboard components, it runs at a certain multiple of the FSB
speed. Sometimes this muliplier can be adjusted, and sometimes not.
Sometimes you can "unlock" the multiplier of a CPU using BIOS tweaks and
more involved workarounds. -Dave
 
Tim said:
I have a few questions regarding the FSB and how it affects the CPU ...

1) Are FSB frequency pulses generated from within the CPU itself or from
somewhere else? Where is the oscillator (if that's what it's called), and
where is the multiplier?

2) Hypothetically, if you have a processor with a 1GHz speed rating, which
it achieves using 100 MHz FSB and a 10x multiplier, what happens when you
achieve that 1GHz using an overclocked FSB and a lower multiplier? Does it
put a strain on the CPU, even though the final CPU speed is still running at
its intended frequency?

Thanks in advance.
Click to expand...

Yes, there's an oscillator, on the main board as part of the clock
generator. That clock generator provides the clock for the FSB, which also
goes into the processor.

The multiplier is in the processor and is input to a phase locked loop
which multiplies up the FSB clock for the internal processor clock.

In almost all modern processor the multiplier is unchangeable (possible to
do since it's in the processor and if it won't accept changes then it can't
be changed).

If you increase the FSB, and lower the multiplier, it will have no effect
on the processor core but the FSB buffers, and internal L2 cache if it has
any, will be at the faster speed. The issue would be if it can run that
fast, not if it's 'hurt' by it.
 
I have a few questions regarding the FSB and how it affects the CPU ...

1) Are FSB frequency pulses generated from within the CPU itself or from
somewhere else? Where is the oscillator (if that's what it's called), and
where is the multiplier?
Click to expand...

You choulde see a crystal with the 14.31818 Mhz value, and a chip with
probably an ICS logo. The 14.31818 Mkz chip produces the root system
clock, the ICS chip multiplies it to the FSB frequency. The CPU itself
multiplies the FSB to the rated clock frequency.
 
If you increase the FSB, and lower the multiplier, it will have no effect
on the processor core but the FSB buffers, and internal L2 cache if it has
any, will be at the faster speed. The issue would be if it can run that
fast, not if it's 'hurt' by it.
Click to expand...

I assume that this speed issue would also pertain to the northbridge, since
the FSB connects to that also, correct?
 
Gary Tait said:
You choulde see a crystal with the 14.31818 Mhz value, and a chip with
probably an ICS logo. The 14.31818 Mkz chip produces the root system
clock, the ICS chip multiplies it to the FSB frequency. The CPU itself
multiplies the FSB to the rated clock frequency.
Click to expand...


Thanks!
 
Dave C. said:
Second half of number one . . . as the CPU must run at a speed much higher
than most motherboard components, it runs at a certain multiple of the FSB
speed.
Click to expand...

Thanks for the info.

Sometimes this muliplier can be adjusted, and sometimes not.
Sometimes you can "unlock" the multiplier of a CPU using BIOS tweaks and
more involved workarounds. -Dave
Click to expand...

That's precisely why I'm asking, I'm interested in overclocking one of the
mobile Bartons.
 
If you increase the FSB, and lower the multiplier, it will have no effect
on the processor core but the FSB buffers, and internal L2 cache if it has
any, will be at the faster speed.
Click to expand...

But aren't today's CPUs, with onboard L2 cache, usually running the cache at
core speed anyway?
 
Tim said:
But aren't today's CPUs, with onboard L2 cache, usually running the cache at
core speed anyway?
Click to expand...

Well, the processor side of it is, yes. The other side is at FSB.
 
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