The behavior of the air flow inside a hard disk drive is evaluated by a three-dimensional unsteady-flow analysis technique called large eddy simulation (LES). The simulation shows that the fluctuation of the aerodynamic force is strongly correlated with the amplitude of the disk vibration, which causes positioning error of the readwrite head. It also shows that the power loss caused by the friction of the air on the disks, which accounts for most of the power consumption of hard disk drives at a high-speed revolution, can be qualitatively predicted.