Abstract: A data storage system having a number of disk drives is disclosed. Each disk drive is provided with a disk spindle driven by a spindle motor. The disk spindle is utilized for mounting one or more disks whose surface is used for data storage. A read/write head mounted on an actuator is provided for each disk surface. Each read/write head is positioned over a desired location on the disk surface by a control mechanism in order to transfer data to and from the disk surface. Data and position information are encoded on each disk surface according to a pre-specified format. The rotation of the disk spindle is controlled to maintain a desired angular position and velocity. A sensor signal indicative of the disk spindle angular position and velocity is obtained independently of the position information encoded on the disk surface. A reference signal, which is obtained from the disk surface, is combined with the sensor signal to adjust the angular position of the disk spindle.