Between 25MHz and 5GHz - it depends on the CPU
Often moden CPU's it's linked to the speed of the CPU (ie 3GHz Core 2 has 3GHz cache)... But the latest CPU's with level 3 cache have this running at a lower speed, but level 1 and 2 at full speed...
Such an open ended question - do you have a specific CPU in mind
THANKS MY Dear FRIEND