This paper investigates the rotating effect on the natural frequency of a cylindrical shell and a center clamped disk to a shaft. In the first part, the equation of a motion of a cylindrical shell is derived by using Hamilton's principle and the characteristic equation is solved to find the travelling wave frequencies. The natural frequencies of the micromachined ring type gyroscope is then obtained by analyzing a long cylindrical shell. In the second part, the equation of motion of the hard disk drive spindle system includes the equivalent stiffnesses associated with cover, base and flange. It is shown that simmulated natural frequencies of the system are in good agreement with the experimental measurements, by introducing the effective clamping radius of disk as well as the equivalent stiffness.