Computer Dictionary of Information Technology

clock

A circuit in a processor that generates a regular sequence of electronic pulses used to synchronise operations of the processor's components. The time between pulses is the cycle time and the number of pulses per second is the clock rate (or frequency).

The execution times of instructions on a computer are usually measured by a number of clock cycles rather than seconds. Clock rates for various models of the computer may increase as technology improves, and it is usually the relative times one is interested in when discussing the instruction set.