# FSB speed and CPU speed - I don't understand the relationship



## Josh2004 (Nov 2, 2008)

I am trying to understand the relationship between FSB speed and CPU speed. I did some reading and thought I understood that the speed of the CPU is the speed of the FSB multiplied by the CPUs multiplier but then I started looking at some CPUs on Newegg and this didn't really make since when checking out the specs. I looked at the Intel Pentium E5200 Wolfdale 2.5GHz and saw that the FSB speed is 800 mhz and the CPU speed is 2.5 ghz. So what is the multiplier of the cpu? Can the multiplier be a decimal number? 

Another thing I'm not quite understanding when looking at motherboards is the FSB speed listed for the motherboard. Is this spec the highest possible speed this motherboard support or this the speed that motherboard has to run at? When picking out a motherboard do I just want to make sure the FSB speed is at least as high as the FSB speed of the CPU?

Any one last question about FSB speed. Is the speed listed the actual speed or is it what it amounts to based on double pumping or quad pumping?

I'm just trying to understand the relationship between all these different numbers I see everywhere. It gets a little confusing. Thanks for any help you can provide.

Edit: I have a few additional questions I'm not quite sure on.

When it comes to RAM speed do I want to make sure the speed of the ram is at least as fast as the FSB speed in order to prevent a bottleneck? 

I'm not quite understand the function of the L1 and L2 cache. Is information fed through the FSB and then certain info that is used frequently then scooted over to one of the chaches? What determines which code goes to the cache? Is this determined by the OS or this determined by the way the program you are running is written?


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