According to one embodiment, a magnetic disk device includes a disk, a head which writes data to the disk and reads data from the disk, and a controller which increases a first recording density of data to be written to a first sector having a first overwrite in the first sector and reduces a second recording density of data to be written to a second sector having a second overwrite different from the first overwrite, on a first track of the disk.

Provided are an apparatus and a method for generating a reproduction signal with reduced laser noise. There are provided a photodetector (PD) that irradiates a disk with laser light and outputs a signal based on a reflected light from the disk, a front monitor that outputs a reference signal based on an emitted light of a laser diode, and a data detection processing unit to which an output signal of the PD is input to generate a reproduction signal. The data detection processing unit includes a reproduction signal adaptive equalizer that outputs an equalization signal by adaptive equalization processing based on the PD output signal, and a laser noise adaptive equalizer that outputs the equalization signal by the adaptive equalization processing based on a laser noise signal, and generates the reproduction signal in which the laser noise is reduced on the basis of an arithmetic operation result of the output of the reproduction signal adaptive equalizer and the output of the laser noise adaptive equalizer.

A reproducing device (100) includes (i) an optical pickup (6) for irradiating, with reproduction light, an optical disk (1) which is a super-resolution medium, (ii) an RF signal processing circuit (9) for converting, into a reproduction signal, light which reflected off optical disk (1), (iii) an i-MLSE detecting section (141) for evaluating quality of the reproduction signal, and (iv) a spherical aberration correcting section (142) for correcting a spherical aberration by using a result of evaluation of the quality of the reproduction signal.

A reproducing device (100) includes (i) an optical pickup (6) for irradiating, with reproduction light, an optical disk (1) which is a super-resolution medium, (ii) an RF signal processing circuit (9) for converting, into a reproduction signal, light which reflected off optical disk (1), (iii) an i-MLSE detecting section (141) for evaluating quality of the reproduction signal, and (iv) a spherical aberration correcting section (142) for correcting a spherical aberration by using a result of evaluation of the quality of the reproduction signal.

A reproducing device (100) includes (i) an optical pickup (6) for irradiating, with reproduction light, an optical disk (1) which is a super-resolution medium, (ii) an RF signal processing circuit (9) for converting, into a reproduction signal, light which reflected off optical disk (1), (iii) an i-MLSE detecting section (141) for evaluating quality of the reproduction signal, and (iv) a spherical aberration correcting section (142) for correcting a spherical aberration by using a result of evaluation of the quality of the reproduction signal.

A reproducing device (100) includes (i) an optical pickup (6) for irradiating, with reproduction light, an optical disk (1) which is a super-resolution medium, (ii) an RF signal processing circuit (9) for converting, into a reproduction signal, light which reflected off optical disk (1), (iii) an i-MLSE detecting section (141) for evaluating quality of the reproduction signal, and (iv) a spherical aberration correcting section (142) for correcting a spherical aberration by using a result of evaluation of the quality of the reproduction signal.

In a storage device, data is written to tracks on a storage medium. Data for each track includes a preamble. The preamble in any current track is orthogonal to the preamble in any track adjacent to the current track. A first read head is positioned over the current track and off-center toward a first adjacent track on a first side of the current track to detect first signals from among the current track, the first adjacent track, and a second adjacent track on a second side of the current track. A second read head is positioned over the current track and off-center relative to the current track toward the second adjacent track to detect second signals from among the current track, the first adjacent track, and the second adjacent track. Analyzing the first and second signals determines an amount by which the read heads are off-track from the current track.

A reproducing device (100) includes (i) an optical pickup (6) for irradiating, with reproduction light, an optical disk (1) which is a super-resolution medium, (ii) an RF signal processing circuit (9) for converting, into a reproduction signal, light which reflected off optical disk (1), (iii) an i-MLSE detecting section (141) for evaluating quality of the reproduction signal, and (iv) a spherical aberration correcting section (142) for correcting a spherical aberration by using a result of evaluation of the quality of the reproduction signal.

An inspection method for a recordable optical disc includes focusing laser light on a recording layer and obtaining a data signal dependent on the laser light reflected by the recording layer. The inspection method also includes determining whether the optical disc includes a defect or not by identifying a first period every second period in the obtained data signal obtained, the first period being a period in which a signal level of the data signal is lower than a predetermined value, and each of the second periods corresponding to an ECC block, and outputting a result of the determination.

An inspection method for a recordable optical disc includes focusing laser light on a recording layer and obtaining a data signal dependent on the laser light reflected by the recording layer. The inspection method also includes determining whether the optical disc includes a defect or not by identifying a first period every second period in the obtained data signal obtained, the first period being a period in which a signal level of the data signal is lower than a predetermined value, and each of the second periods corresponding to an ECC block, and outputting a result of the determination.