Magnetic disk system having servo signal detecting function depending on

Abstract

Servo data respectively recorded in the peripheral and innermost tracks of a magnetic disk at low and high densities in synchronism with a predetermined write period are read back and binarized by the magnetic head as flux reversal patterns. In this case, on the basis of a table stored in the EEPROM in advance, the filter characteristic of a characteristic variable type low-pass filter is variably set to be a characteristic defined by a low cutoff frequency fc and a small boost amount in the peripheral zone and to be a characteristic defined by a high cutoff frequency and a boost amount, which is large on a high-frequency side, on the central zone. The peak waveforms of a servo signal in the central side are raised to be sharpened, and a qualification level in a pulse decoder is variably set to be high in the outermost tracks and to be low in the innermost tracks. The low-pass filter receives a servo signal output from an AGC amplifier, removes a specific frequency component from the servo signal in accordance with a set filter characteristic, and sends the resultant signal to the pulse decoder as a servo signal. The pulse decoder converts the servo signal, which is uniform in the peripheral and innermost tracks of the disk, into a binary pulse in accordance with the set qualification level.