WHy does the CPU has a GHz speed and a lower FSB speed?

[Lonkut]

I don't understand what the two speeds are for. Can anybody briefly explain the difference between the GHz and FSB speed and what they do?

 

[GVBN]

Front side bus * multiplier = frequency

 

[Chairman Meow]

The FSB speed is the speed at which the main memory (RAM) operates. It is typically slower than the CPU speed, because the RAM takes longer to read/write addresses than the CPU does to go through one clock cycle. The RAM is located outside of the CPU chip, and it takes time for the signals from the processor chip to reach the RAM than it does, for example, for the CPU to access its registers, which are basically just on-chip memory.

 

[Quintillus]

So, that means that, if, for example, I had a 400MHz CPU FSB, and 400 MHz memory, it would do me no good to upgrade to 533 MHz memory (assuming everything else stayed the same)?

 

[Comraddict]

So, that means that, if, for example, I had a 400MHz CPU FSB, and 400 MHz memory, it would do me no good to upgrade to 533 MHz memory (assuming everything else stayed the same)?

Yes, exactly. Running memory off sync is undesired. Running it at lower speed than CPU is ok, just something that is unavoidable if you have slower memory; but running it faster than FSB is not good idea.

Memory has its timings, which means there are other factors that influence its performance at certain MHz. By rule, memory has better timings if it runs on lower frequency. Thus, if memory is 533MHz and FSB is 400MHz, it is best to run it at 400MHz.