What is the Real FSB Frequency?

[RonAKA]

I had my E4300 overclocked to 3 GHz on my P5B DX, but was forced into replacing the MB. I now have a Gigabyte EP45-UD3R and would like to OC to a similar value. The last overclocking I did was a couple of years ago, and my knowledge has slipped some.

Is this correct, using the E4300 in stock setup as an example? The FSB frequency from the Northbridge is 200 MHz. This is multiplied by the CPU multiplier of 9 to get the CPU to run 1.8 GHz. The memory multiplier/divider multiplies the 200 by 5/3 to get 333 MHz which is then doubled to get a memory frequency of 667 MHz.

Is the FSB frequency 200, 1800, or 667? or ?? To confuse me further I see the old board was rated at a FSB of 1066, 800, or 533, while the new one does 1600, 1333, 1066, & 800.

Will the real FSB frequency please stand up...

 

[Nickel020]

The FSB frequency is 200 MHz, Intel calls it 800 MHz quad-pumped FSB, because for bits of data are transferred every clockcycle (i.e. Hz)

The RAM actually runs at 333Mhz but is marketed as 667MHz, since it transfers two bits per clockcycle, effectively reaching the speed of (non-existing) RAM that runs at 667MHz but only transfers one bit per cycle.

The FSB that a board is rated at only concerns the FSB it supports, the FSB which the system is actually running is determined by the CPU you're using. So if you're using your E4300 with an effective FSB of 800 (200 MHz real FSB) on a X48 chipset board that supports FSB 1600 (400 MHz real), then the FSB will still be 800 (200 MHz real).

PS: The FSB is the link between the CPU and the northbridge, so there only always is one FSB frequency, there are no seperate NB FSB and CPU FSB frequencies.

 

[RonAKA]

Thanks for the reply. It is starting to come back to me. To confirm my understanding, are you really saying that when Gigabyte says the the MB supports FSB of 1600, 1333, 1066, and 800, you have to divide these by 4 to get the actual FSB frequencies of 400, 333, 266, and 200? And why do they pick out these specific frequencies when you can actually set the FSB to any number withing the overall range? Or are these the frequencies that they provide multipliers for that match the common memory speeds?

 

[BlueAcolyte]

Originally posted by: RonAKA
Thanks for the reply. It is starting to come back to me. To confirm my understanding, are you really saying that when Gigabyte says the the MB supports FSB of 1600, 1333, 1066, and 800, you have to divide these by 4 to get the actual FSB frequencies of 400, 333, 266, and 200? And why do they pick out these specific frequencies when you can actually set the FSB to any number withing the overall range? Or are these the frequencies that they provide multipliers for that match the common memory speeds?

The FSB can be set in increments of 1, but these are the most common speeds.

 

[LokutusofBorg]

The different CPUs have a different stock FSB. The E5xxx series and below are 800MHz. E7400 jumps up to 1066 and the E8xxx are 1333. Your old board wouldn't have been able to run one of the E8xxx CPUs, for example. (It isn't rated to, at least.)

 

[Nickel020]

I'm really saying that the FSB does not run at 1600, 1333, 1066 or 800 but at 400, 333, 266 and 200 MHz respectively. It does transfer 4 bits of data per cycle though so it's effectively running at the higher speeds.

The FSB is not set or picked by GB but set by Intel and determined by the CPU you use. You can of course set it manually, but at stock it will always run at the value that Intel programmed into the CPU.