DC computer case fans operate based on the principles of electromagnetism and aerodynamics. The fan consists of a motor, blades, and a housing.

The motor is the heart of the fan. It contains a stator and a rotor. The stator is a stationary part with coils of wire, while the rotor is a rotating part with permanent magnets. When an electric current is applied to the coils in the stator, it creates a magnetic field. This magnetic field interacts with the magnetic field of the permanent magnets on the rotor, causing the rotor to rotate.

The blades of the fan are attached to the rotor. As the rotor spins, the blades also rotate. The shape and angle of the blades are designed to create a pressure difference. When the blades rotate, they push air in one direction. According to the laws of aerodynamics, air moves from an area of high pressure to an area of low pressure. So, as the blades push air in one direction, more air is drawn in from the other side, creating a continuous flow of air.

The speed of the fan can be adjusted in different ways. For fans connected to a 3 - pin header, the speed can be adjusted by changing the voltage supplied to the fan. Reducing the voltage decreases the speed of the motor and thus the fan blades. For 4 - pin PWM fans, the speed is controlled by the PWM signal, which effectively changes the amount of time the fan is powered on and off within a given period, adjusting the average power and thus the speed.