Answer : 3. "Clock speed"
Explanation :

1. Clock speed is used to measure the speed of the processor.

2. Clock speed is the rate at which a processor can complete a processing cycle. It is usually measured in megahertz or gigahertz.

3. One megahertz is equal to one million cycles per second, while one gigahertz is equal to one billion cycles per second. This means that a 1.8 GHz processor has twice the clock speed of a 900 MHz processor.