Abstract: A servo controller for correcting a read position of a head when reading data recorded on a recording medium. In accordance with the amplitude ratio of data signals read from each segment of a servo section defined on a recording medium, the servo controller generates an AGC signal corresponding to the next segment before reading the next segment. The data signal read from a phase detection segment of the servo section is amplified to an amplitude greater than the predetermined determination range. The amplified data signal is converted to a two-value digital signal in accordance with the determination range. The phase used during servo control is calculated in accordance with the digital signal.

Abstract: A method for using a nibble(partial bits of word) inversion code in a network system includes the steps of: a) adding 1 redundancy bit to n bit source data and generating a pre-code, n being an even number of 2 or over; b) deciding the number of transitions in the generated pre-code; c) determining the pre-code as a code word if the number of transitions in the pre-code is greater than or equal to 1+n/2 in a deciding result; d) inverting alternate bits including the redundancy bit among bits constructing the pre-code and generating the code word, if the number of transitions in the pre-code is less than n/2 in the deciding result; e) determining the pre-code as the code word in case that the number of transitions in the pre-code is equal to n/2 and simultaneously the source data is not an in-band signaling and not a special word in the deciding result; and f) inverting the nibble among the bits constructing the pre-code and generating the code word, in case that the number of transitions in the pre-code