Abstract: In a conventional disk drive device using concentric servo tracks to operate data heads on concentric data tracks, a second mode of operation is provided which is compatible with the use of concentric servo tracks for driving the data heads in a spiral, continuous mode for accessing all of the data on a particular disk surface in a single data read or data write operation. A conventional computer system disk drive could be modified for occasional use in storing and retransmission of video signals. In the preferred embodiment of the invention, each servo track is provided with a once per revolution clock pulse which starts the operation of an integrator. The integrator generates a time varying signal of the same period as the time for one revolution of the disk pack. An error signal is generated by conventional means to indicate the error in position of the servo tracking head with respect to the servo track.