James Hanley wrote:
David Maynard wrote in message ...

James Hanley wrote:


David Maynard wrote in message ...


James Hanley wrote:



it seems to me that nobody needs a high fsb. since they could just
push the multiplier really high.

I can see the greatness of ddr since the same speed processor can
read/write twice as much per cycle. (i assume that the cpu has to be
ddr to receive or write double)

How is it you can see the benefit to 'read/write twice as much per cycle'
yet not see any benefit to more of the cycles?


Obviously I see the benefit of more cycles. What do you think I meant
when I said "push the multiplier really high". That increases the
cycles per second.

No, increasing the multiplier does NOT increase the FSB cycles.


I knew that, it increases cycles per second, but just CPU cycles.
So yeah. I just realised that:
Increasing the multiplier increases CPU cycles (not FSB cycles of
course).
Increasing the FSB increases both - that is what hadn't occurred to me
:P

It isn't because of increasing 'both': that's a matter of the CPU
multiplier being locked, or not.

A 1.83 Ghz processor on a 333 Mhz FSB will perform better than a 1.83 Ghz
processor running on a 266 Mhz FSB, whether you accomplish the test by
buying two different processors or using one with an adjustable multiplier.

It isn't as dramatic an improvement as changing the CPU speed (multiplier)
partly because it's offset by the L2 cache.


So if the system supported it(processor was unlocked and very
underclocked) doubling the FSB is better than doubling the current
value of the multiplier.

It depends on what you mean by that.

If you mean taking a processor of speed X on FSB Y and *either* doubling
the FSB *or* doubling the CPU speed then no, doubling the FSB, alone, is
not as good as doubling the CPU speed, alone.

If you mean, as I suspect you do, doing one or the other to end up with the
same CPU speed after it's all said and done, then yes, because a processor
at speed X will perform better if it also has a faster FSB (within reason).

Let's put it to a practical example. I have an unlocked mobile Barton 2400
on a DFI motherboard that let's me adjust everything, so I can run it
overclocked to 2.2 Ghz at 266 Mhz FSB, 333 Mhz FSB, or 400 Mhz FSB (if I
stay at 'standard' FSBs) by adjusting the multiplier accordingly. Which do
you think will give me the best performance?

It's better to have a faster FSB(thus
increasing CPU cycles and FSB cycles) than to have a slower FSB and a
larger multiplier, which would only increase CPU cycles.

You're mixing apples and oranges. In one case you alter the CPU speed but
not in the other. That might be a constraint imposed when using a locked
multiplier CPU but it confuses the matter that increasing the FSB, alone,
improves processor performance because more instructions can get to it per
second.


More CPU cycles -- more CPU bandwidth

No. More 'CPU cycles' (all else being equal) --- more instructions
executed per second, assuming it can GET the instructions at that rate.

More FSB cycles -- more FSB bandwidth

I suppose bandwidth and throughput are the same thing

Bandwidth is capability and throughput is what is actually going through.


thanks for your response