A Fluid Dynamic Bearing (FDB) is a type of bearing primarily used in fans and motors, including those in computer water cooling systems. Its principle involves separating moving parts with a thin layer of fluid, most often oil. During shaft rotation, hydrodynamic pressure is generated in the fluid, creating a "fluid cushion" that prevents direct contact between metal surfaces. This minimizes friction and wear. Compared to simpler sleeve or ball bearings, FDB bearings are characterized by quieter operation, as the fluid effectively dampens vibrations. Additionally, thanks to reduced wear and a sealed design that prevents lubricant leakage and dust ingress, they offer a longer lifespan and higher reliability.