PWM stands for pulse width modulation. PWM fans and/or pumps are found in some CPU coolers and GPU (aka graphics card) coolers. They use an integrated circuit to control the speed of a fan or pump and, therefore, how much cooling it’s providing to the CPU or GPU. PWM fans and pumps can alter their speed and airflow based on the component's temperature.
To use this feature, you’ll need a motherboard with a PWM header and the appropriate software (for help shopping, see our motherboard buying guide). Most mainstream motherboards have at least one 4-pin PWM header, and the best motherboards usually have to four to six. Note, older fans may use 3-pin connectors.
PWM works like a switch, turning on and off while controlling the level of power delivered to the fan or pump. PWM fans works in correlation with the motor, receiving full power or zero power.
PWM is also used in servo motors, voltage regulation, telecommunications and audio equipment.
This article is part of the Tom's Hardware Glossary.