Clock and Clock Speed

The clock is a component inside the CPU that sends a regular series of pulses, or ticks, like a metronome keeping a band in time. These pulses synchronise and regulate the actions of the CPU, so its components work together in the correct order and at the right moments.

Each step of the fetch-decode-execute cycle is triggered by a pulse from the clock. For example, a pulse marks the moment the CPU stops fetching an instruction and starts to decode it. The pulse carries no instruction or data: it is a timing signal telling the CPU when to move on to the next step. The clock never stores data or does calculations — it only times the CPU's work.

Clock speed

Clock speed, also called clock frequency, is the number of clock cycles that happen each second, where one cycle is one complete pulse. A faster clock produces more pulses each second, so the CPU is prompted to work through its steps more often.

Units of clock speed

Clock speed is measured in hertz (Hz), where one hertz means one cycle per second. Each unit is one thousand times larger than the one before it:

So 1 MHz is 1,000 kHz and 1 GHz is 1,000 MHz, which means the units are not close in size at all.

Why a higher clock speed matters

A higher clock speed means more cycles each second, so more instructions are processed in a given time. For example, a 2.4 GHz processor completes 2,400,000,000 cycles every second and a 3.2 GHz processor completes 3,200,000,000, so the faster chip has an extra 800,000,000 cycles each second to spend fetching, decoding and executing. It can usually work through more instructions in the same time.