What is PWM and DC in BIOS?

In a computer’s BIOS there are two control modes for regulating fan speeds PWM (Pulse Width Modulation) and DC (Direct Current). If we understand these modes we can improve noise levels and cooling issues.

PWM Mode:

Uses a 4-pin fan connector.
The fan motor is regulated by fan speed which electrical pulses are provided by it to send in the varying width to the electrical fan motor.
It allows for finer control of fan speed, down to 20 to 100 percent maximum RPM.
At lower speeds, where modern cooling solutions are used, PWM is more efficient and quieter.
DC Mode:

Uses a 3-pin fan connector.
Serves to control fan speed (that is, adjust voltage to the fan depending on voltage (12V for Maximum RPM, lower voltages for reduced speed))
But not as old and not as precise as PWM, and works with older hardware.
Key Differences:
DC fans can use up to 3W full speed, whereas PWM fans will consume less, around 0.5-1W.
The BIOS allows you to switch between PWM and DC fan control manually or on modern motherboards the type is often automatically detected.
Expert Insights:
For modern CPU and GPU cooling, use PWM because it’s flexible and precise, DC is ok for case fans, and legacy systems.