A disk drive controller including a preamplifier and a controller is disclosed, in which communications between the controller and the preamplifier are carried out over at least some shared terminals and conductors. A first pair of differential lines is provided to communicate data, sensed at read/write heads of the disk drive, from the preamplifier to the controller, and a second pair of differential lines communicates data to be written to the disk drive from the controller to the preamplifier. Control signals are communicated over a serial interface between the controller and preamplifier, over the first pair of differential lines, so that serial communication can be carried out simultaneously with the writing of data from the controller to the preamplifier. Alternatively, the control signals are communicated over the second pair of differential lines, simultaneously with the reading of data from the preamplifier to the controller.