Measures how quickly the CPU processes data?

Answer 1

Clock Speed

Edit: Not really. Clock speed alone has a very small effect on the processing power of a CPU. Allow me, as pasted from another similar answer:

Most basic? Clock speed along with operations per clock cycle.

This measures how frequently the processor processes data and how much it can process each frequency "tick" Clock speed's nice, but more operations per cycle is far more important.

Cache hit rate, pipeline length, cache miss recovery cycle time, integer unit efficiency, MMX processing power, FSB speed, thermal efficiency, etc can all change how powerful and fast a processor is. Cache hit / miss rate and recovery time have just as substantial effect on processing power as the clock speed does.