Abstract: A data-storage system comprises a head receiver configured to variably receive up to a number M of write heads. The data-storage system also includes an installed number N of write heads arranged in the head receiver, a substrate receiver configured to receive one or more data-storage substrates, and a positioner machine configured to adjust a relative placement of each of the M write heads with respect to at least one of the one or more data-storage substrates.

Abstract: A magnetic disk device includes a case including a magnetic disk, a magnetic head configured to read or write data from or to the magnetic disk, an actuator configured to move the magnetic head, and a humidity sensor positioned within the case to measure a humidity in the case and output a measurement value; a control circuit configured to calculate a value of a voltage to be applied to the actuator based on a displacement amount of the magnetic head and the measurement value output from the sensor, and output the calculated value; and a servo controller configured to control the actuator by applying the voltage to the actuator according to the value output by the control circuit.

Abstract: A method includes processing, via an integrated circuit, data read from a first servo wedge; processing, via the integrated circuit, data from a second servo wedge; and skipping processing data from a third servo wedge positioned between the first servo wedge and the second servo wedge.

Abstract: A dual-stage servo system of a disk drive includes a first fine positioning servo system with a first microactuator that independently controls the position of a first read/write head over a first recording surface and a second fine positioning servo system with a second microactuator that independently controls the position of a second read/write head over a second recording surface. The first microactuator accesses a first data stripe while the second fine positioning servo system simultaneously accesses a second data stripe. Data can be transferred to or from the first and second data stripes simultaneously.

Abstract: According to one embodiment, a magnetic disk device including a disk, a head, and a controller which sets a first track pitch based on fringing when a second track is written, sets a second track pitch based on fringing when a third track is written, calculates a difference between the first track pitch and the second track pitch, sets, when the difference is less than or equal to a reference value, an area to which the first track is written in a first recording area, and sets, when the difference is greater than the reference value, the area to which the first track is written in a second recording area.

Abstract: A data storage device includes a first system-on-a-chip (SOC) associated with a first read transducer that accesses one or more magnetic disks of the data storage drive. The first SOC has a first read channel operable to receive data from the first read transducer. A second SOC is associated with a second read transducer that accesses the one or more magnetic disks of the data storage drive independently of the first read transducer. The second SOC has a second read channel operable to receive second data from the second read transducer. The first and second SOCs are coupled via a data bus that facilitates communicating the first and second data to a host via a first host interface.

Abstract: A magnetic disk device includes a magnetic disk and a control circuit. The magnetic disk includes a first area where writing is performed in a manner such that a newly written track partially overlaps a previously written adjacent track. The control circuit is configured to specify a range of a second track, which is to be overlapped as a result of writing first data to a first track, write second data written in the specified range of the second track to a saving area prior to writing the first data to the first track, write the first data to the first track, and verify the second data in the second track after writing the first data to the first track.

Abstract: A method according to one embodiment includes generating a y-position estimate based on a servo readback signal, and determining a nonlinearity-correction value corresponding to the y-position estimate. The method further includes adjusting the y-position estimate using the nonlinearity-correction value. A computer program product for compensating for nonlinearity in a timing based servo pattern according to another embodiment includes a computer readable storage medium having program instructions embodied therewith. The program instructions are readable and/or executable by a controller to cause the controller to perform the foregoing method. An apparatus according to another embodiment includes a controller configured to perform the foregoing method.

Abstract: A media device may comprise a controller, a tape head, a tape comprising tape-position indicia, an indicia detection device, and an adjusting device. The indicia detection device may be configured to detect the tape-position indicia and provide an output corresponding to a tape position. The controller may be configured to send an adjustment command based on the output. The adjusting device may be configured to adjust the media device between a first configuration and a second configuration, based on the adjustment command. The tape may physically contact the tape head in the first configuration and not physically contact the tape head in the second configuration.

Abstract: In a position detector for converting, into position information, two signals shifted in phase by 90 degrees from each other, a phase correction value calculator for calculating a phase correction value for correcting a phase difference between the two signals calculates a phase change value representing a change in the phase correction value, to find a next phase correction value based on the phase change value and a present phase correction value. A virtual change value calculator calculates, based on second-order components obtained by Fourier analysis of a radius value, a virtual phase change value representing another change in the phase correction value obtained when changes in offset and amplitude ratio are ignored, and a virtual amplitude change value representing a change rate in an amplitude ratio correction value obtained when a change in the phase difference is ignored.

Abstract: An apparatus configured to characterize a magnetic recording tape of a tape cartridge, according to one embodiment, includes a magnetic head having servo readers of known pitch, a drive mechanism for passing a magnetic recording tape over the magnetic head, and a controller electrically coupled to the magnetic head. The controller is configured to measure, using signals from the magnetic head, a servo band difference at various locations along a length of the magnetic recording tape of a tape cartridge. The controller is also configured to store the servo band difference measurements and/or derivatives thereof in association with the tape cartridge.

Abstract: A system accesses metadata on a file system of the magnetic tape, where the metadata comprising one or more fields enabling to determine a longitudinal position (LPOS) of one or more files located on the magnetic tape. The system determines the LPOS of the one or more files located on the magnetic tape. The system determines an optimal location of the head on the magnetic tape based on computing an average value to the determined LPOS of the one or more files located on the magnetic tape and moves the head on the magnetic tape to the optimal location.

Abstract: Disclosed are mixtures containing: mono- and bi-functional polymers [polymers (P-A) and (P—B)] comprising a plurality of (per)fluoropolyether segments [segments (SRF)] joined together by hydrogenated (poly)ether segments [segments (SH)], said polymers having two ends, wherein one or both ends comprises a hydroxy or a leaving group; a non-functional polymer comprising a plurality of (per)fluoropolyether segments (SRF) joined together by hydrogenated (poly)ether segments (SH), with the proviso that the hydrogenated (poly)ether segments (SH) are not segments of formula —CH2OCH2OCH2—. Disclosed are also monofunctional polymers (P-A) that can be isolated from such mixtures. Methods for the obtainment of the mixtures and for separating the polymers therein contained are also provided, as well as methods of using the mixtures or each polymer therein contained as intermediates or building blocks for the synthesis of other polymers or as ingredients of compositions.

Abstract: In some embodiments, apparatuses and methods are provided herein useful to a test card for use in automated testing of a POS terminal. In some embodiments, the test card comprises a substrate including at least one track, wherein the substrate is configured to interact with a magnetic card reader, an electrical contact configured to receive magnetic stripe data from a database, and an electrical trace, wherein the electrical trace is programmable with respect to the received magnetic stripe data, wherein the electrical trace forms a continuous conductive pathway, wherein the electrical trace forms a stair step configuration comprising a plurality of linear segments including a first set of linear segments and a second set of linear segments, wherein the second set of linear segments includes at least one segment, and wherein the at least one segment connects ones of the first set of linear segments.

Abstract: The magnetic tape device includes a magnetic tape including a magnetic layer, in which an intensity ratio of a peak intensity of a diffraction peak of a (110) plane with respect to a peak intensity of a diffraction peak of a (114) plane of a hexagonal ferrite crystal structure obtained by an X-ray diffraction analysis of the magnetic layer by using an In-Plane method is 0.5 to 4.0, a vertical direction squareness ratio of the magnetic tape is 0.65 to 1.00, Ra measured regarding a surface of the magnetic layer is equal to or smaller than 2.0 nm, and a C—H derived C concentration calculated from a C—H peak area ratio of C1s spectra obtained by X-ray photoelectron spectroscopic analysis performed on the surface of the magnetic layer at a photoelectron take-off angle of 10 degrees is 45 to 65 atom %.

Abstract: According to one embodiment, a magnetic disk device includes a disk, a head, and a controller that estimates a first frequency component resulting from a disturbance in a first range of a frequency corresponding to the disturbance in a signal with the disturbance, estimates a second frequency component corresponding to a second frequency of a positive integral multiple of 2 or larger of a first frequency of the first frequency component in a second range different from the first range, and suppresses a first harmonic component corresponding to the positive integral multiple of the first frequency in a position error of a target position of the head on the disk.

Abstract: The magnetic tape device includes a TMR head (servo head); and a magnetic tape, in which a magnetic layer of the magnetic tape includes fatty acid ester, Ra measured regarding a surface of the magnetic layer is equal to or smaller than 2.0 nm, full widths at half maximum of spacing distribution measured by optical interferometry regarding a surface of the magnetic layer before and after performing a vacuum heating with respect to the magnetic tape are greater than 0 nm and equal to or smaller than 7.0 nm, a difference between spacings before and after the vacuum heating is greater than 0 nm and equal to or smaller than 8.0 nm, and ?SFD (=SFD25° C.?SFD?#° C.) in a longitudinal direction of the magnetic tape is equal to or smaller than 0.50.

Abstract: First and second tracks are read simultaneously via a first reader mounted in a head-gimbal assembly. The first reader provides a first signal based on detecting a total perpendicular field of the first and second tracks. The first and second tracks are read simultaneously via a second reader mounted in the head-gimbal assembly. The second reader provides a second signal based on detecting a total longitudinal field of the first and second tracks. At least one of a position error and a timing error of at least one of the first and second readers are determined based on user data read via the respective first and second signals.

Abstract: According to one embodiment, a semiconductor device includes a semiconductor element, and a first member. The first member includes a first nonmagnetic planar region separated from the semiconductor element in a first direction, a first magnetic planar region provided between the first nonmagnetic planar region and the semiconductor element in the first direction, and a second nonmagnetic planar region provided between the first magnetic planar region and the semiconductor element in the first direction. The first magnetic planar region includes a first end portion extending along a second direction crossing the first direction. A first magnetization direction of the first magnetic planar region is tilted with respect to the second direction.

Abstract: Systems and methods for servo zone transition optimization are described. In one embodiment, the storage system device includes a disk drive and a controller. In some embodiments, the controller may be configured to assess at least one operation of a read/write head of the disk drive; and format, based at least in part on the assessing of the read/write head, a disk surface of the disk drive with a first servo zone, a second servo zone, and an overlap region extending between a start point of the second servo zone and an end point of the first servo zone. In some cases, the overlap region starts towards a disk inner diameter (ID) and ends towards a disk outer diameter (OD).

Abstract: The present disclosure provides a feedback control system and method for a bidirectional VCM. The system employs an analog core that is common to both the PWM and linear modes of operation. The analog core includes a feedback mechanism that determines the error in the current flowing through the motor. The feedback mechanism produces an error voltage that corresponds to the current error, and applies the voltage to a control driver. The control driver then controls the motor, based on the error voltage, in either a PWM or linear mode. By sharing a common core, the switching time between modes is improved. Furthermore, the output current error between modes is reduced.

Abstract: An electronic device is installed in a machine where there is a possibility in occurrence of vibration or impact. The electronic device includes an acceleration detecting unit detecting acceleration in a predetermined time interval, and an impact determining unit. In a case where it is determined that an acceleration value exceeds a predetermined first threshold value, a second threshold value is calculated based on a maximum value among acceleration values of plural accelerations for a predetermined time interval after the determination. In a case where the number of accelerations where acceleration values exceeds the second threshold value among the plural accelerations is a predetermined number or less, the impact as a single-type impact is determined. In a case where the number exceeds the predetermined number, the impact as a multiple-type impact is determined. Also included is an output unit outputting a signal in a case where the impact is determined as the multiple-type impact.

Abstract: Disclosed herein are circuits, architectures, and methods that provide for the control of a data storage device write head's trailing shield and main pole potential with respect to the disk using circuitry that is integrated with circuitry used to bias a spin torque oscillator (STO) apparatus. Various embodiments include slider connections with STO bias circuitry that resides in a read/write integrated circuit, which has a programmable circuit that generates a bias current with overshoot (bias kicks). Also disclosed are circuits that may be incorporated into a slider to mitigate radio-frequency interference.

Abstract: An error detection device includes a generation unit and a detection-correction unit. When writing data into a storage unit, the generation unit generates error detection information for each piece of division-data into which write-data are divided. The error detection information is information which is available in determining whether a bit error includes in the division-data, and by which a position where the bit error is caused can be detected based on plural pieces of the error detection information of the plural division-data composing the write-data. Using the error detection information, the detection-correction unit can determine whether the bit error is caused in the division-data. Using plural pieces of the error detection information of the data including the division-data in which it is detected that the bit error is caused, the detection-correction unit can detect the position where the error is caused, and can correct the bit error.

Abstract: The present disclosure provides a method and system for data persistence in stream computing, and the present disclosure belongs to the technical field of data storage. The method comprises: initiating, by a management module, a task; extracting a key corresponding to the task from a data source based on the task; acquiring a value corresponding to the key from the data source based on the key, performing data processing to generate intermediate data and a first signal, and storing the intermediate data and the first signal; detecting whether the first signal has been stored, and sending detection information to the management module. By using the present disclosure, the intermediate data persistence result may be effectively fed back, such that the intermediate data persistence may be ensured to be transactional.

Abstract: In some examples, a portable electronic device may monitor a plurality of device care metrics to detect and characterize a level of care provided to an electronic device by a user. Further, the user may receive a reward for providing a level of care as specified by one or more device care thresholds. For example, the device may monitor sensor information from one or more sensors for determining whether the device has experienced a physical event, such as a fall event, an excessive moisture event, or the like. Further, the device may also monitor for system events, such as whether to update a program, whether malicious code has been installed, or the like. The occurrence of a physical event and/or the user's actions in response to a system event may determine a user's eligibility to receive a reward based on the level of device care provided.

Abstract: A method and system for determining slider-disk contact in a hard-disk drive (HDD) that has dual independent heaters for thermal fly-height control, and dual embedded contact sensors, includes dithering power to the two heaters at different frequencies. The HDD has the two contact sensors electrically connected to provide a single combined output signal in response to the dithering. The single combined output signal is analyzed to detect two signals at the two different frequencies. When either detected signal exceeds a predetermined touchdown threshold value, the values of heater power for the two heaters are recorded, indicating that that combination of heater power values corresponds to slider-disk contact.

Abstract: A control device includes an interface for exchanging data with a servo driver. The servo driver is configured to execute a control arithmetic operation in which a manipulation amount for driving the servo motor is determined on the basis of a control parameter determined in accordance with a control target. The control device includes a creation unit that acquires the control parameter of the servo driver and creates an internal model representing a motion characteristic of the control target, and a target value calculation unit that calculates a corrected target value to be supplied to the servo driver on the basis of a target value corresponding to a target track and a feedback value from the control target.

Abstract: The magnetic tape device includes a magnetic tape including a magnetic layer, in which an intensity ratio of a peak intensity of a diffraction peak of a (110) plane with respect to a peak intensity of a diffraction peak of a (114) plane of a hexagonal ferrite crystal structure obtained by an X-ray diffraction analysis of the magnetic layer by using an In-Plane method is 0.5 to 4.0, a vertical direction squareness ratio of the magnetic tape is 0.65 to 1.00, Ra measured regarding a surface of the magnetic layer is equal to or smaller than 2.0 nm, and a C—H derived C concentration calculated from a C—H peak area ratio of C1s spectra obtained by X-ray photoelectron spectroscopic analysis performed on the surface of the magnetic layer at a photoelectron take-off angle of 10 degrees is 45 to 65 atom %.

Abstract: A positioning control device of an actuator provided with a strain wave gearing has a full-closed control system for feeding back a position of a load shaft, and driving and controlling a motor so as to position the load shaft at a target position. The full-closed control system has an H? compensator designed so that, when a generalized plant having angular transmission error in the strain wave gearing as a disturbance input is assumed, an H? norm of a transfer function from the disturbance input of the generalized plant to an evaluation output is a predetermined value or less. Mechanical vibration during positioning response caused by angular transmission error in the strain wave gearing can be reliably suppressed.

Abstract: A clearance heater of a write head is engaged with a boosted current that exceeds a steady-state current. The steady-state current causes the write head to maintain a desired clearance over a disk during writing, the boosted current being applied before a start of the writing. The boosted current is monotonically decreased before the start of the writing and the steady-state current is applied to the heater after the start of the writing.

Abstract: Embodiments of the present disclosure relate to a method and an apparatus for operating a hybrid storage device, the hybrid storage device including a storage device of a first type and a storage device of a second type that is different from the first type, the method comprising: synchronously writing data in the storage device of the first type and the storage device of the second type. By using the embodiments of the present disclosure, the actual storage space may be increased, and the service life of the storage device may be prolonged.

Abstract: A spin-orbit torque type magnetization reversal element including a ferromagnetic metal layer with a varying magnetization direction; and spin-orbit torque wiring that extends in a first direction intersecting with a stacking direction of the ferromagnetic metal layer and that is joined to the ferromagnetic metal layer; wherein when viewed from the first direction, the spin-orbit torque wiring is asymmetrical in a second direction that is orthogonal to the first direction and the stacking direction, with respect to an axis that passes through a center, in the second direction, of the ferromagnetic metal layer.

Abstract: According to one embodiment, a servo write control apparatus is for a disk apparatus including a read element and a write element located in an outer side of a disk from the read element. The servo write control apparatus detects a plurality of first burst signals recorded in a circumferential direction of the disk by the read element. The servo write control apparatus calculates an offset in a radial direction when the write element writes a second burst signal, based on amplitude values of at least two of the first burst signals used for positioning the read element. The servo write control apparatus adjusts a write position of the second burst signal based on the offset.

Abstract: Operations include compensating for a Tracking Error Signal (TES) offset in an optical tape drive. The tracking error offset compensation system detects a control signal for controlling movement of an optical head across a surface of a tape. The tracking error offset compensation system computes an estimated movement of the optical head, based on the initial control signal. The tracking error offset compensation system determines an estimated TES offset, based on the estimated movement of the optical head. The tracking error offset compensation system uses the estimated TES offset to correct a TES. The tracking error offset compensation system transmits the corrected TES, for controlling additional movement of the optical head.

Abstract: An apparatus may include a first and second servo channels configured to output first and second position information to first and second writers, respectively, via a shared write path such that the first and second writers write first and second position information to first and second magnetic recording medium surfaces, respectively. In addition, the apparatus may include a controller configured to control the shared write path such that write access is changed between the first servo channel and second servo channel a plurality of times during a revolution of the first magnetic recording medium surface and second magnetic recording medium surface.

Abstract: Method and apparatus for predicting data storage device failures using adaptive failure prediction modeling. In some embodiments, monitored parameters are used to predict a potential imminent failure of a first data storage device using a first copy of a first failure prediction model (FPM). Data associated with the predicted potential imminent failure are transferred by the device across a computer network to a host device. The host device generates an updated, second FPM responsive to the transferred data as well as from data from at least a second data storage device transmitted across the computer network having a second copy of the first FPM. A first copy of the updated, second FPM is transferred, via the network, for use by the second data storage device.

Abstract: A tape transport control system with enhanced regulation of tape tension and velocity over the entire length of the tape. For example, a closed-loop control system for controlling a tape transport includes circuitry adapted to output a signal representing a tape velocity at a tape head, circuitry adapted to output a signal representing a tape velocity at the first tape reel and a signal representing a tape velocity at the second tape reel, circuitry adapted to output a signal representing a tape tension, and circuitry adapted to, based on the received signals, generate control signals to control the tape velocity at least at one of the tape head, the first tape reel, the second tape reel, and the tension of the tape, using controller gains that depend on a longitudinal position of the tape, and to implement a system transfer function that is approximately independent of the longitudinal position.

Abstract: A plurality of commands is received from a host to perform at least one of reading data and writing data on a magnetic storage media of a Data Storage Device (DSD). The plurality of commands is clustered for performance based at least in part on a timing control of a fly-height heater of the DSD that is configured to adjust a flying height of a head of the DSD while the head is flying over the magnetic storage media. A cluster of commands is performed including the plurality of commands by controlling the head to perform at least one of reading and writing data on the magnetic storage media for the cluster of commands.

Abstract: A magnetic recording apparatus includes a magnetic recording medium; a magnetic recording head including a first magnetic pole part, a second magnetic pole part, and a magnetic flux control part provided between the first magnetic pole part and the second magnetic pole part, wherein the magnetic flux control part includes a first layer provided between the first magnetic pole part and the second magnetic pole part, a second layer provided between the first magnetic pole part and the first layer, and a third layer provided between the second magnetic pole part and the first layer; an electrode for applying a current to the magnetic flux control part; and an electric circuit for energizing the current to the electrode, wherein an oscillation frequency of magnetization of the magnetic layer is greater than a ferromagnetic resonance frequency of the magnetic recording medium.

Abstract: A disk device includes first and second recording surfaces, a first head for the first recording surface, including a first heater which generates heat via a first electric power, a second head for the second recording surface, including a second heater which generates heat via a second electric power, and a control circuit configured to execute a first preheating operation in which the first electric power is supplied to the first heater for a first time interval prior to starting a first writing process to write data on the first recording surface by the first head, and to execute a second preheating operation in which the second electric power is supplied to the second heater for a second time interval prior to starting a second writing process to write data on the second recording surface by the second head. The first time interval is different from the second time interval.

Abstract: Systems and techniques for communicating data as a function of frequency are presented. In an implementation, a system includes a microelectromechanical systems (MEMS) sensor, a digital signal processor and a frequency detection circuit. The digital signal processor is coupled to the MEMS sensor. The frequency detection circuit receives data encoded as a function of frequency from the digital signal processor via a clock communication channel.

Abstract: A magnetic disk device includes a disk, a head configured to write data on the disk, and a controller. The controller generates a target trajectory of the head in a circumferential direction for writing to a plurality of sectors in a current track, wherein the target trajectory is based on an actual trajectory of the head for writing to a plurality of sectors in a previously written track that is adjacent to the current track, determines that the previously written track is discontinuous between an initial sector of the previously written track and an end sector of the previously written track by a radial offset, generates a corrected trajectory for writing the plurality of sectors in the current track, and controls a position of the head in a radial direction based on the corrected trajectory while writing to the plurality of sectors in the current track.

Abstract: The magnetic tape device includes a magnetic tape including a magnetic layer, in which an intensity ratio of a peak intensity of a diffraction peak of a (110) plane with respect to a peak intensity of a diffraction peak of a (114) plane of a hexagonal ferrite crystal structure obtained by an X-ray diffraction analysis of the magnetic layer by using an In-Plane method is 0.5 to 4.0, a vertical direction squareness ratio of the magnetic tape is 0.65 to 1.00, Ra measured regarding a surface of the magnetic layer is equal to or smaller than 2.0 nm, and a C—H derived C concentration calculated from a C—H peak area ratio of C1s spectra obtained by X-ray photoelectron spectroscopic analysis performed on the surface of the magnetic layer at a photoelectron take-off angle of 10 degrees is 45 to 65 atom %.

Abstract: The magnetic tape device includes a magnetic tape including a magnetic layer, in which an intensity ratio of a peak intensity of a diffraction peak of a (110) plane with respect to a peak intensity of a diffraction peak of a (114) plane of a hexagonal ferrite crystal structure obtained by an X-ray diffraction analysis of the magnetic layer by using an In-Plane method is 0.5 to 4.0, a vertical direction squareness ratio of the magnetic tape is 0.65 to 1.00, Ra measured regarding a surface of the magnetic layer is equal to or smaller than 2.0 nm, and a C—H derived C concentration calculated from a C—H peak area ratio of C1s spectra obtained by X-ray photoelectron spectroscopic analysis performed on the surface of the magnetic layer at a photoelectron take-off angle of 10 degrees is 45 to 65 atom %.

Abstract: A microactuator for a suspension is described. The microactuator includes a multi-layer PZT device having a first face and an opposite second face. Each layer of the multi-layer PZT device is configured to operate in its d15 mode when actuated by an actuation voltage. The layers are configured as a stack such that each layer is configured to act in the same direction when actuated such that the first face moves in shear relative to the second face.

Abstract: A servo control device according to the present invention includes a speed command generation unit, a torque command generation unit, a speed detection unit, a speed control loop, a speed control gain setting unit for setting a speed control gain for the speed control loop, a sinusoidal disturbance input unit for performing a sinusoidal sweep on the speed control loop, a frequency characteristic calculation unit, and a gain adjustment unit. When the speed control loop has fallen into an oscillation state and has become unstable owing to the increased speed control gain, the speed control gain is reduced and the sinusoidal sweep is temporarily stopped. After the speed control loop is stabilized using the speed control gain which is lower than in the unstable state, the sinusoidal sweep is restarted.

Abstract: A PZT microactuator such as for a hard disk drive has a restraining layer bonded on its side that is opposite the side on which the PZT is mounted. The restraining layer comprises a stiff and resilient material such as stainless steel. The restraining layer can cover most or all of the top of the PZT, with an electrical connection being made to the PZT where it is not covered by the restraining layer. The restraining layer reduces bending of the PZT as mounted and hence increases effective stroke length, or reverses the sign of the bending which increases the effective stroke length of the PZT even further. The restraining layer can be one or more active layers of PZT material that act in the opposite direction as the main PZT layer. The restraining layer(s) may be thinner than the main PZT layer.

Abstract: During in-drive writing of a servo spiral on a disk surface, a servo spiral can be distinguished during demodulation from adjacent servo spirals on the same disk surface. When a set of servo spirals is written on a disk surface, a first spiral is written to include a first identifying characteristic and the following spiral is written to include a second identifying characteristic. The identifying characteristic may include embedded sync marks encoding a certain numerical value, a unique frequency of high-low transitions included in each spiral, and/or a unique frame size.

Abstract: A hard disk drive (HDD) is configured to move a read head over a region of a storage surface that includes unreadable segments of reference spirals that have been overwritten by a reference spiral in a set of spirals that is currently being written on the storage surface. By moving the read head across the region of the storage surface at a return radial velocity that is selected such that the write head crosses no consecutive reference spirals at an unreadable segment, the servo system of the HDD does not experience an error due to crossing multiple consecutive reference spirals at unreadable segments. Thus, a set of spirals that includes partially damaged reference spirals can be employed to control the position of a read head. Consequently, a second surface is not required for the set of spirals employed in controlling the writing process.