The motherboard CPU fan interface is a crucial connection point for cooling the CPU. It allows the motherboard to supply power to the CPU fan and, in some cases, control its speed. There are mainly two types of common interfaces: 3-pin and 4-ppin. The 3-pin interface consists of a power pin, a ground pin, and a tachometer pin. The power pin provides the electrical energy to drive the fan's motor. The ground pin completes the circuit. The tachometer pin sends a signal back to the motherboard indicating the fan's rotational speed. This enables the motherboard to monitor if the fan is working properly and at what speed. However, with a 3-pin interface, the motherboard can't directly control the fan's speed in a very precise way.

The 4-pin interface, also known as a PWM (pulse width modulation) interface, has an extra pin. This PWM pin allows the motherboard to send a signal that can vary the voltage supplied to the fan in a rapid on-off cycle. By adjusting the duty cycle of this signal, the motherboard can precisely control the fan speed. For example, when the CPU is idle and generating less heat, the motherboard can reduce the fan speed to minimize noise. When the CPU is under heavy load and producing more heat, it can increase the fan speed to enhance cooling. Some motherboards also have additional fan headers with different power ratings and features. These headers can be used to connect case fans or other cooling fans in the system. The proper connection and configuration of the CPU fan interface are essential for maintaining the CPU's temperature within a safe range and ensuring the overall stability and performance of the computer system.