Essentials of Computer Organization and Architecture, 5th Edition

4.4   CLOCKS

Every computer contains an internal clock that regulates how quickly instructions can be executed. The clock also synchronizes all of the components in the system. As the clock ticks, it sets the pace for everything that happens in the system, much like a metronome or a symphony conductor. The CPU uses this clock to regulate its progress, checking the otherwise unpredictable speed of the digital logic gates. The CPU requires a fixed number of clock ticks to execute each instruction. Therefore, instruction performance is often measured in clock cycles—the time between clock ticks—instead of seconds. The clock frequency (sometimes called the clock rate or clock speed) is measured in megahertz (MHz) or gigahertz (GHz), as we saw ...