Abstract: An apparatus and method of indirectly measuring half frequency whirl in a spindle motor having a rotor adapted to rotate a disc having a track which is followed by a transducer head that is actuated by a control system is provided. Vibration signals produced at the transducer head while the transducer head follows the track are detected. The half frequency whirl is determined as a function of the detected vibration signals.

Abstract: A crash stop assembly limits pivotal movement of an actuator assembly mounted on a base plate of a disc drive. The disc drive includes a signal channel extending from the actuator assembly to a disc drive circuit board, and the crash stop assembly includes a connector bracket secured to the base plate and supporting the signal channel. The crash stop assembly further includes a crash stop secured to the connector bracket and extending therefrom, and the crash stop includes a contact surface that contacts the actuator assembly to limit pivotal movement of the actuator assembly.