What sets the FSB?

[nheather]

I have an Intel E6750 on an Abit IP35.

The CPU runs at 2.666GHz with an FSB of 1333MHz.

The SoftMenu settings have the following

External Clock - 333
Multiplier - 8
RAM - 1:1.2

I can understand that

CPU = 333 x 8 = 2664
RAM = 333 x 1.2 x 2 = 799.2

But what determines the FSB?

I assume it's running at 1333MHz but is it fixed, or related to external clock.

In other words if I increased External Clock to 350 what would happen to FSB? My guess is that it will be 1400MHz but I'm not certain.

Thanks for the help,

Cheers,

Nigel

 

[95thrifles]

Your external clock is your FSB, theres actually 2 FSB values, your real/actual value, which is 333, and the rated value which is the real value quad pumped = 333x4=1333. So yeah if you change your external clock to 350, your rated FSB would become 1400. as I said your actual FSB is the 350 though, this is the speed your computer uses to talk to other components, the rated FSB is only relevant to the CPU and is quad pumped because of the naumber of channels/lanes (I get mixed up with my terminology at times )
If you go into the overclocking section theres a couple of stickies at the top about OC'ing for beginners and they explain a little bit about the terms etc

 

[errata]

as above the external clock sets your base fsb for communcication across the mobo with the processor and ram, separate multipliers then apply for ram and cpu to get the speed ratings we all know so well

the cpu fsb speed is usually quoted as the quad version as the magic of intels archtecture manages to pass 4 bits of data for each external clock tick

so 333 x 4 is the 1333 often quoted, if you do nothing else raising the ext clock 1 will increase the cpu 4

dual core cpu's come in 800 fsb (200 x4 ) 1066 (266 x 4 ) 1333, 1600 (400 x 4)

for ddr or ddr2 ram it is indeed 333 x 1.2 x 2 as the magic of ddr2 passes 2 bits per clock tick and its got a 1.2 multiplier from the motherboard chipset

If you raised your ext clock to 350 the proccesorw would gain speed ((350-333) x 4)
and the memory (350-333) x 2 both woudl be overclocked

if the cpu can take it but not the memory then you would change the memory multiplier to somhning less say 1:1.1 so 350 *1.1 * 2 = 770 or relax some ram timngs or increase ram voltage

 

[nheather]

Thanks for the replies.

So the RAM 400MHz and 800MHz, the CPU 2.66GHz and the CPU 1333MHz are clocks that exist only with the RAM and the CPU.

The highest frequency on the MoBo is the external clock.

Yes I will step down my RAM timings - unfortunately, my MoBo is a bit limited on available ratios - essentially I can have 1:1 or 1:1.2 - all the others are higher. It would have been nice to have something in between but I don't have that luxury so I'll have to make do with 1:1 but perhaps I'll be able to tighten the timings or reduce the voltage to compensate.

Cheers,

Nigel

 

[Big.Wayne]

if I increased External Clock to 350 what would happen to FSB? My guess is that it will be 1400MHz but I'm not certain.

Hey nheather,

you basically have it right although your jargon isn't quite right!

The thing you are reffering to as External Clock is actually called the FSB!

The thing you are reffering to as FSB is actually called System BUS!

so using your processor to clarify:

• Intel® Core™2 Duo Desktop Processor E6750
  
  • Front Side Bus (FSB) = 333MHz
  • Multi = x8
  • System Bus = 1333MHz
  • Memory = 333MHz (minimum)
  • Effective Memory= 666MHz or DDR2-666

The base figure is the FSB, all other frequencies are based on this through divison or multiplication!