The analysis of the head positioning error is one of the most important themes for increasing the areal storage density of magnetic disk drives. In this paper, the sensitivity of the position error signal (PES) is corrected for its nonlinearity with an adaptive gain estimator. PES is divided into the repeatable positioning error (RPE) and the non-repeatable positioning error (NRPE). RPE is transformed into the repeatable head displacement (RHD) which is evaluated in the track width variance and the write-to-read track misregistration (TMR). NRPE is decomposed into its contributing components which are the mechanical vibration, the flutter vibration, the position sensing noise and the force disturbance. Finally, NRPE is transformed into the real NRPE which doesn't include the position sensing noise.