Motherboard FSB Speed - how does it effect other components?

[ryan d ale]

Hi.

I was wondering what the FSB (Front Side Bus) does for a motherboard and it seems that it is what allows the other hardware to interact with it.

The speed of the FSB on the Mobo I'm thinking of getting is 6400Mhz.

However, when I combine the RAM speeds (3X1333Mhz) and speeds of the clocks inside the graphics card it overruns that of the FSB. Is that going to be a problem?

I read somewhere that modern mobos feature indepedent FSBs for the graphics card and some other hardware but I'm finding it hard to find spec details on this.

Is the motherboard FSB only important for interactions between the mobo and the CPU?

Or am I right? (I'm never right and I would place a bet that this is no exception)

Thanks.

[VoXiNaTiOn]

By the 6.4Ghz link and the 3 sticks of RAM I'm guessing this is the X58 chipset.



The FSB on a motherboard is basically how the components all interact with each other via the NB.

In terms of independent bus speeds, these are the things connected with the south bridge, so your HDDs, Optical drives and GCards. You can't change the SATA frequency, however you can change the PCI-E frequency, however this gives little benefit and only really, in rare cases, allows a slightly higher FSB (Iirc, may be wrong there)




The memory will connect to the FSB with a divider (Basically a ratio) this allows the FSB to stay at full speed and the RAM to stay at full speed. For example lets say the FSB is 266Mhz (Working with the old P45 style chipsets due to being more familiar with them (however this will be a bit sketchy as my mobo works out the dividers for me and simply let's me choose a speed)) and you have PC2-8500 RAM (1066Mhz)

To get the full speed of the memory you would use a 1:2 divider for FSB : DRAM meaning the RAM speed will be double that of the FSB (So the FSB will be 266 and the RAM 532.) Due to this being DDR2 (Double Data Rate 2) you double that figure to get the external speed, giving you the 1066Mhz speed.




To give a real world example, here's my RAM.


(Please note that due to clockspeed fluctuations and the fact they are never 100% what you set them, figures are regularly 1-4Mhz or so out)
(I also know my RAM is in single channel, it throws up a fuss in the form of a BSOD and previously killing a stick of RAM when it is in dual channel)


My FSB is 350Mhz (To give a 350x10 = 3.5Ghz clockspeed on the CPU.)


The divider is 2:3 FSB : DRAM, so 350/2 = 175

175*3 = 525

(Due to it being DDR2) 525*2 = 1050Mhz, giving my effective RAM speed.




With DDR3 the concept remains the same, except to get the effective speed you triple it (DDR3)



Hope this helps, AgentJadeD should be able to give some more info in relation to X58 and it's QPI speed as opposed to FSB, however the concept remains the same but simply uses a multiplier on the memory instead of a divider.

[ryan d ale]

That was an excellent explanation.

Things make much more sense now.

I really appreciate it that, thanks.

[VoXiNaTiOn]

No worries, here to help .

Shout if you need anything else explained and someone here will be able to make it clear.