Various illustrative aspects are directed to a data storage device comprising one or more disks, an actuator assembly comprising one or more disk heads; and one or more processing devices, configured to detect a plurality of areas with a coercivity lower than a threshold on the one or more disks; map out one or more sectors in each of the plurality of lower coercivity areas on the one or more disks; write data to, or read data from, the one or more disks, based at least in part on mapping out the one or more sectors in each of the plurality of lower coercivity areas. In some embodiments, the writing or reading data comprises writing data to, or reading data from, one or more sectors of the one or more disks that are not mapped out.

According to one embodiment, in a magnetic disk, a plurality of first servo sectors is arranged at intervals in the circumferential direction. Each of the plurality of first servo sectors includes a first area and a second area. First information including a preamble, a servo mark, and a Gray code is written in the first area. The second area is disposed after the first area in a write and read direction along the circumferential direction, and second information including a burst pattern is written in the second area. The plurality of first servo sectors includes a plurality of second servo sectors and a plurality of third servo sectors. The circumferential length of a first area included in each of the plurality of third servo sectors is longer than the circumferential length of a first area included in each of the plurality of second servo sectors.

According to one embodiment, a magnetic disk device, includes a disk including a track including a plurality of servo sectors, a head including a write head which writes data to the disk and a plurality of read heads which read the data from the disk, and a controller configured to simultaneously acquire a plurality of pieces of correction data for repeatable runout of the disk by the read heads, acquire a first correction data and a second correction data based on the correction data, write the first correction data and the second correction data to the disk, and correct a position of the head based on the first correction data and the second correction data.

According to one embodiment, in a magnetic disk, a plurality of first servo sectors is arranged at intervals in the circumferential direction. Each of the plurality of first servo sectors includes a first area and a second area. First information including a preamble, a servo mark, and a Gray code is written in the first area. The second area is disposed after the first area in a write and read direction along the circumferential direction, and second information including a burst pattern is written in the second area. The plurality of first servo sectors includes a plurality of second servo sectors and a plurality of third servo sectors. The circumferential length of a first area included in each of the plurality of third servo sectors is longer than the circumferential length of a first area included in each of the plurality of second servo sectors.

According to one embodiment, a magnetic disk device, includes a disk including a track including a plurality of servo sectors, a head including a write head which writes data to the disk and a plurality of read heads which read the data from the disk, and a controller configured to simultaneously acquire a plurality of pieces of correction data for repeatable runout of the disk by the read heads, acquire a first correction data and a second correction data based on the correction data, write the first correction data and the second correction data to the disk, and correct a position of the head based on the first correction data and the second correction data.

According to one embodiment, in a disk device, the head includes a first read element and a second read element. The disk medium is partitioned into a plurality of zones. The plurality of zones include a first zone and a second zone. The first zone includes a plurality of tracks on each of which a servo area and a data area are placed, a servo burst region in the servo area from which to detect the amount of off-track of the head from the center of a track, having a first bit length. The second zone includes a plurality of tracks on each of which a servo area and a data area are placed, a servo burst region in the servo area from which to detect the amount of off-track of the head from the center of a track, having a second bit length shorter than the first bit length.

According to one embodiment, in a disk device, the head includes a first read element and a second read element. The disk medium is partitioned into a plurality of zones. The plurality of zones include a first zone and a second zone. The first zone includes a plurality of tracks on each of which a servo area and a data area are placed, a servo burst region in the servo area from which to detect the amount of off-track of the head from the center of a track, having a first bit length. The second zone includes a plurality of tracks on each of which a servo area and a data area are placed, a servo burst region in the servo area from which to detect the amount of off-track of the head from the center of a track, having a second bit length shorter than the first bit length.

A magnetic disk device according to one embodiment includes a magnetic disk on which multiple tracks are provided, a magnetic head, and a controller. At least one of the multiple tracks includes first sectors and a second sector. Each of the first sectors stores data segments. The second sector stores a parity for error correction. The magnetic head executes writing/reading to/from the magnetic disk. The controller executes processing of adjusting a guaranteed number of times by using a second sector being invalid. The guaranteed number of times indicates a number of times of writing for guaranteeing reading from an adjacent track.

According to one embodiment, in a disk device, a controller adjusts a correction value of a radial position of servo track according to a ratio between amplitude of a correction value spectrum of a radial position of the servo track at a first circumferential position and at a second circumferential position when positioning control of the head to a target data track is performed on a basis of servo information read from the servo track. At the first circumferential position, a relative speed of a change in the radial position of the servo track with respect to a radial position of the target data track becomes a first speed. At the second circumferential position, a relative speed of a change in the radial position of the servo track with respect to the radial position of the target data track becomes a second speed.

Various illustrative aspects are directed to a data storage device including one or more disks, an actuator mechanism configured to position a selected head among one or more heads proximate to a corresponding disk surface among the one or more disks, the selected head comprising a write element and an assistive energy emitter, and one or more processing devices configured to, individually or in combination: apply an assistive energy current to the assistive energy emitter while refraining from applying a write current to the write element, and vary a level of the assistive energy current over time while refraining from applying the write current to the write element.