A disk drive includes a rotatable data storage disk, a transducer, an actuator, and a servo burst demodulator. In a magnetic disk drive according to one embodiment, vibration of a headslider can be detected with a vibration sensor attached to a head support mechanism. The mixer is further coupled to a demodulator and filter which in turn is coupled to an amplifier and a comparator. The index table generation unit allocates continuous index values to the existing brightness values, and stores the result of allocation into an index memory table. The same operation may be effected regarding accelerator.