A data storage device is disclosed comprising a head actuated over a disk. A test pattern is read from a first part of the disk to generate a first read signal that is sampled to generate a first sequence of signal samples. The test pattern is read from a second part of the disk to generate a second read signal that is sampled to generate a second sequence of signal samples. A third sequence of signal samples is generated by at least one of amplitude-inverting the second sequence of signal samples, time-inverting the second sequence of signal samples, and amplitude-inverting and time-inverting the second sequence of signal samples. A quality metric is generated based on the first sequence of signal samples and the third sequence of signal samples, and a data density of the disk is configured based on the quality metric.

In an optical disc apparatus that records and reproduces data onto and from an optical disc in units of predetermined block, an information divider divides the data so as to reduce an amount of the data included in each of blocks when a recording state of the optical disc does not satisfy a predetermined criterion, and reproduces recording data in units of the block by adding sub-information including a value indicating the amount of the data included in each of the blocks. An error-correction encoder circuit encodes the recording data in a first error-correction code format, and a recorder converts encoded recording data into a recording signal, and records the recording signal onto the optical disc. A quality evaluator circuit produces an evaluation value indicating a recording quality based on a result of reproducing the recording signal recorded on the optical disc.

A data storage device is disclosed comprising a head actuated over a disk. A test pattern is read from a first part of the disk to generate a first read signal that is sampled to generate a first sequence of signal samples. The test pattern is read from a second part of the disk to generate a second read signal that is sampled to generate a second sequence of signal samples. A third sequence of signal samples is generated by at least one of amplitude-inverting the second sequence of signal samples, time-inverting the second sequence of signal samples, and amplitude-inverting and time-inverting the second sequence of signal samples. A quality metric is generated based on the first sequence of signal samples and the third sequence of signal samples, and a data density of the disk is configured based on the quality metric.

To obtain a signal quality evaluation value capable of having a high correlation to an error rate and high accuracy for a reproduction signal of high density recording. For the object, an estimated value of a path selection error rate is obtained on the basis of a distribution of a path metric difference between a maximum likelihood path at each time, which is a detection path in maximum likelihood decoding in a PRML decoding system and a second path having a second highest likelihood. Further, an average error bit number in erroneous detection is obtained from a bit difference number between the maximum likelihood path and the second path at the time of path selection of each time in the maximum likelihood decoding. In addition, an estimated bit error rate is obtained from results and an evaluation value according to the estimated bit error rate is generated.

A data storage device is disclosed comprising a head actuated over a disk comprising a plurality of tracks. A first degradation metric is maintained for a first segment of a first track, wherein the first degradation metric indicates a degree of degradation for data recorded in the first segment. The first degradation metric is processed to select an access command from a plurality of access commands including a read command to read the first segment. The selected access command is executed to access the disk.

A data storage device is disclosed comprising a head actuated over a disk comprising a plurality of tracks. A first degradation metric is maintained for a first segment of a first track, wherein the first degradation metric indicates a degree of degradation for data recorded in the first segment. The first degradation metric is processed to select an access command from a plurality of access commands including a read command to read the first segment. The selected access command is executed to access the disk.

To obtain a signal quality evaluation value capable of having a high correlation to an error rate and high accuracy for a reproduction signal of high density recording. For the object, an estimated value of a path selection error rate is obtained on the basis of a distribution of a path metric difference between a maximum likelihood path at each time, which is a detection path in maximum likelihood decoding in a PRML decoding system and a second path having a second highest likelihood. Further, an average error bit number in erroneous detection is obtained from a bit difference number between the maximum likelihood path and the second path at the time of path selection of each time in the maximum likelihood decoding. In addition, an estimated bit error rate is obtained from results and an evaluation value according to the estimated bit error rate is generated.

In an optical disc apparatus that records and reproduces data onto and from an optical disc in units of predetermined block, an information divider divides the data so as to reduce an amount of the data included in each of blocks when a recording state of the optical disc does not satisfy a predetermined criterion, and reproduces recording data in units of the block by adding sub-information including a value indicating the amount of the data included in each of the blocks. An error-correction encoder circuit encodes the recording data in a first error-correction code format, and a recorder converts encoded recording data into a recording signal, and records the recording signal onto the optical disc. A quality evaluator circuit produces an evaluation value indicating a recording quality based on a result of reproducing the recording signal recorded on the optical disc.

A method for writing data onto a medium on which data are stored in tracks includes encoding the data into at least one codeword, and writing a respective portion of each of the at least one codeword onto respective different tracks on the medium. The writing may include writing a respective portion of each of the at least one codeword onto respective different adjacent tracks on the medium. Another method for reading data includes positioning a plurality of read heads to read codewords that have been written across multiple tracks of a medium. Each read head in the plurality of read heads reads a different portion of the first group of the multiple tracks, and where each different portion of the multiple tracks overlaps at least one other different portion of the multiple tracks. Signals are detected from the plurality of read beads, and the detected signals are decoded.

Techniques for verifying a magnetic tape are disclosed. The techniques include obtaining a position signal generated by reading a magnetic tape using a stationary tape head. Next, a simulated current for adjusting a position of the tape head to follow a track on the magnetic tape is updated using the position signal. The simulated current is then compared to one or more saturation limits to generate a verification result for a servo pattern on the magnetic tape, wherein the verification result classifies the magnetic tape as usable or unusable. Finally, the verification result is outputted for use in managing subsequent use of the magnetic tape.