A clock governs the operation of a CPU. The clock ticks so many times per second. The time difference between two consecutive ticks is the time of a processing cycle which is the minimum time needed by the CPU to perform an operation. Hence, CPU speeds are measured by clock rates. Clock rates (number of processing cycles per second) are measured in hertz (named after a German scientist), where 1 hertz means 1 cycle per second. The number of processing cycles needed to execute a program instruction determines the instruction execution time. Current microprocessor speeds are expressed in megahertz (1 MHz = 1 million cycles per second) and gigahertz (1 GHz = 1 billion cycles per second). |
