What is FSB?
 

What is Front Side Bus, and how does increased FSB effect your computer?

Front Side Bus is the speed of the motherboard. A processor's speed is a combination of the FSB and the multiplier at the socket. A 1GHz chip could be a 10x chip running on a 100MHz motherboard. Or, it could be a 7.5x chip on a 133MHz motherboard. The multiplier is fixed, and can't be changed... So, if you put the 7.5x chip on the 100MHz motherboard, it would run only at 750MHz.

The FSB is the speed of the memory. The higher the FSB, the faster the memory can transfer data to / from the processor. You can run higher-rated memory on a slower FSB, but not normally vice-versa. Sometimes you can get away with it... A good quality PC100 SDRAM can usually take 133MHz, but don't really count on it.