A processor's speed is dependant on the bus-speed of the computer. Some smart engineer a long, long time ago figured out that it doesnt have to run at the SAME speed as the computer though, but a multiplier of the bus-speed works just as fine. Ie if you have a 600MHz Athlon, which in normal cases runs at a 100MHz bus-speed, it operates with a clock-multiplier of 6.0 (6.0 x 100 = 600MHz).