Abstract: A data playback device includes a laser to produce light to illuminate a disk form of data recording medium and to playback data stored on the disk, the data being recorded on the disk in a first group of data tracks and a second group of data tracks, which exist in concentric or spiral form, wherein the first group of tracks and the second group of tracks exist with a mutual difference in level in the radial direction in the disk form of data recording medium. The data playback device further includes a rotary device to rotate the recording medium, a tracking control unit to cause the illumination location of the laser light to follow the first group of tracks or the second group of tracks, and a setting unit to set the control condition in the tracking control unit for tracking with respect to the first group of tracks or for tracking with respect to the second group of tracks.

Abstract: An optical disk apparatus has a data recording circuit for recording user data in a data portion of a sector on an optical disk. The optical disk is formed with a plurality of tracks in a concentric circular shape or spiral shape on the surface thereof and is possible of data write based on a sector unit. Each track is segmented into a plurality of sectors. The apparatus also has a detection circuit for detecting a resynchro pattern recorded together with user data from a regenerative signal obtained from the data portion of a sector before recording user data in the sector, a count circuit for counting a number of resynchro patterns detected, and an overwrite preventive circuit for stopping recording data on the sector when a count value of the count circuit is not less than a predetermined value.