A system includes a controller and a detector. The controller is configured to read servo spirals written on a magnetic surface of a disk drive. The servo spirals are written on the magnetic surface of the disk drive based on seed wedges. The seed wedges are written on the magnetic surface of the disk drive prior to writing the servo spirals on the magnetic surface of the disk drive. The controller is configured to write a servo pattern on the magnetic surface of the disk drive based on reading the servo spirals written on the magnetic surface of the disk drive. The detector is configured to detect, while reading the servo spiral written on the magnetic surface of the disk drive, interference caused by the seed wedges written on the magnetic surface of the disk drive.

A method for writing servo data includes: writing the servo data as the head moves outwardly towards a radial position on the disk one step at a time, wherein the same address data are written as the head moves outwardly in two consecutive steps, writing the servo data as the head moves inwardly towards the radial position one step at a time, so as to overwrite part of servo data that have been written in a previous step, wherein the same address data are written as the head moves inwardly in two consecutive steps, and writing either one of two-phase burst data, or address data and the other of said two-phase burst data, at the radial position.

Various embodiments provide a Gray code detector that is not designed to look for a specific defect signature, but rather looks for wedges that are in error or close to being in error, as determined through a probabilistic analysis that considers the mean and sigma of a minimum Viterbi Metric Margin (minVMM) distribution of a servo wedge relative to a defined threshold for a Wedge Error Rate (WER).

According to one embodiment, a position detecting device includes a detecting portion which periodically detects a plurality of pieces of information generated in accordance with positional information divided into upper digits and lower digits. The upper digits are further divided into a plurality of pieces of upper digit information equal to the number of the period. The pieces of the upper digit information are obtained in a predetermined order. The lower digits are obtained simultaneously with any one of the pieces of the upper digit information. The positional information is divided so that the number of values, which are obtainable in one piece of the upper digit information provided by dividing the upper digits, and a division number of the upper digits are coprime.

A method of recovering a servo write frequency, to read servo wedge data from a rotating magnetic storage medium having at least one servo wedge that includes a servo preamble written at a known preamble frequency, includes analyzing samples of data read from the rotating magnetic storage medium to identify samples in which energy at the known preamble frequency exceeds a predetermined threshold, declaring the location of the servo preamble based on the identification of the samples in which energy at the known preamble frequency exceeds the predetermined threshold, deriving a phase angle from the samples in which the energy at the known preamble frequency exceeds the predetermined threshold, updating an accumulated phase angle using the derived phase angle, and using the updated accumulated phase angle to start a timing recovery loop to recover the servo write frequency. The analyzing and deriving may be performed using a spectral analysis operation.

Provided herein is a method, including creating a first pattern in a data region of a substrate, and creating a second pattern in a servo region of a substrate. A circumferential line pattern is created overlapping the first pattern to create rectangle-shaped protrusions in the data region of the substrate. A chevron pattern is created overlapping the second pattern to create chevron-derived protrusions in the servo region of the substrate.

A method for writing servo data includes writing servo data as a head moves outward on a disk one step at a time, so as to overwrite part of servo data that have been written in a previous step, writing servo data as the head moves inward on the disk one step at a time, so as to overwrite part of servo data that have been written in a previous step, and writing one of two-phase burst data, or address data and the other of said two-phase burst data, at the radial position, so as to overwrite at least part of servo data written in each last step of the writings as the head moves outward and inward. The same address data are written in two consecutive steps as the head moves outward and as the head moves inward.

According to one embodiment, servo patterns different in servo pattern frequency are recorded in zones divided in a radial direction on a magnetic disc, and the servo patterns in the adjacent zones overlap each other in a predetermined area from a zone servo boundary between the zones, and a determination boundary where it is determined to execute a crossing process is set within the overlapping area of the servo patterns upstream from the zone servo boundary, based on position information on a seek destination and the present position of the magnetic head.

Various illustrative aspects are directed to a data storage device, comprising one or more disks; an actuator mechanism configured to position one or more heads proximate to a corresponding disk surface of the one or more disks; and one or more processing devices. The selected head comprises a write element and an assistive energy emitter. The one or more processing devices are configured to apply an assistive energy current to the assistive energy emitter while refraining from applying a write current to the write element.

Illustrative aspects are directed to a data storage device, comprising disks, an actuator mechanism configured to position heads proximate to the disks, and processing devices, including a memory. The processing devices are configured to: receive data with an indicated address for writing the data to a selected disk; read, from the selected disk, a data sector from a location that comprises the indicated address; integrate the received data with a subset of the sector read from the selected disk, thereby generating a new sector that comprises the received data positioned in the new sector in accordance with the indicated address; detect, while the new sector is in the memory and not yet written to the selected disk, a loss of nominal electrical power to the data storage device; and write, in response to detecting the loss of nominal electrical power, the new sector from the memory to a non-volatile cache.