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A CPU's clock speed represents how many cycles per second it can execute. Clock speed is also referred to as clock rate, PC frequency and CPU frequency. This is measured in gigahertz, which refers to billions of pulses per second and is abbreviated as GHz.
A PC’s clock speed is an indicator of its performance and how rapidly a CPU can process data (move individual bits). A higher frequency (bigger number) suggests better performance in common tasks, such as gaming. A CPU with higher clock speed is generally better if all other factors are equal, but a mixture of clock speed, how many instructions the CPU can process per cycle (also known as instructions per clock cycle/clock, or IPC for short) and the number of cores the CPU has all help determine overall performance.
Note that clock speed differs from the number of cores a CPU has; cores help you deal with less common, time-consuming workloads. Clock speed is also not to be confused with bus speed, which tells you how fast a PC can communicate with outside peripherals or components, like the mouse, keyboard and monitor.
Most modern CPUs operate on a range of clock speeds, from the minimum "base" clock speed to a maximum "turbo" speed (which is higher/faster). When the processor encounters a demanding task, it can raise its clock speed temporarily to get the job done faster. However, higher clock speeds generate more heat and, to keep themselves from dangerously overheating, processors will "throttle" down to a lower frequency when they get too warm. A better CPU cooler will lead to higher sustainable speeds.
When buying a PC, its clock speed is a good measurement of performance, but it’s not the only one to consider when deciding if a PC is fast enough for you. Other factors include, again, bus speed and core count, as well as the hard drive, RAM and SSD (solid-state drive).
You can reach faster clock speeds through a process called overclocking.
This article is part of the Tom's Hardware Glossary.