Abstract: Techniques for writing data to a buffer region of a magnetic disk are described. In one example, a hard disk drive comprises a magnetic disk comprising a data buffer region including a first zone and a second zone. Data may be written to the magnetic disk using shingled magnetic recording (SMR) and the buffer region may be an exception region (E-region). A hard disk drive may be configured to calculate a position accuracy value associated with a data writing head. The hard disk drive may select one of the zones based on the position accuracy value. Further, a selected zone may have a determined zone format. The hard disk drive may be configured to write data to the selected zone using the determined zone format.

Abstract: A disk drive is disclosed comprising a disk comprising tracks defined by servo sectors, a head, and control circuitry comprising a servo control system operable to actuate the head over the disk in response to the servo sectors. The servo control system is configured into a first state, and a position error signal (PES) representing a difference between a target location for the head and a measured location for the head is generated. An actuator control signal is generated in response to the PES, a feed-forward control signal is adapted in response to the servo sectors, and the actuator control signal is adjusted using the feed-forward control signal. The servo control system is configured from the first state to a second state, and a phase of the adaptation of the feed-forward control signal is adjusted based on the second state.

Abstract: Apparatus and method for non-destructive detection of contamination on a slider in a data storage device. In some embodiments, the slider supports a read element adjacent a rotating data recording medium. A non-repeatable runout (NRRO) component of a position error signal (PES) obtained from readback signals transduced from the read element is extracted. A power spectral density (PSD) analysis of the NRRO component is performed to identify a peak power level, and slider contamination is detected responsive to the peak power level.

Abstract: A data storage device is disclosed comprising a head actuated over a disk, and a spindle motor configured to rotate the disk, wherein the spindle motor comprises a plurality of windings. A commutation controller is configured to commutate the windings based on a commutation sequence. Compensation values are generated based on: A1 sin ?1t+B1 cos ?lt where A1 and B1 are adaptable coefficients and ?1 represents a first frequency based on a first mechanical parameter of the spindle motor. The compensation values are used to drive the commutation sequence of the commutation controller.

Abstract: A disk drive is disclosed comprising a servo control system configured to control an actuator for actuating a head over a disk. Servo sectors are sampled at a servo sample frequency fs to generate a position error signal PES(k) that is filtered with a compensator to generate a first control signal u1(k). A first discrete-time sinusoid comprising a sinusoid frequency of fs+?f is added to the first control signal u1(k) to generate a second control signal u2(k). The second control signal u2(k) is applied to the actuator, and a frequency response of the actuator is determined at the frequency |?f|. The frequency response of the actuator is determined at the frequency fs+?f based at least in part on the frequency response of the actuator at the frequency |?f| and a measured signal of the servo control system when applying the second control signal u2(k) to the actuator.

Abstract: According to one embodiment, a data storage apparatus includes a disk, a head and a controller. In each track, first and second correction values for correcting a track runout in synchronization with rotation of the disk are recorded. The first correction value is for a first position located within a first track, and the second correction value is for a second position located within a second track adjacent to the first track, and separated from the first track by a predetermined distance. The head writes data to or read data from the tracks. The controller corrects the track runout with the first and second correction values, when the head is controlled to position at a target track.

Abstract: A disk drive is disclosed comprising a head actuated over a disk comprising a plurality of servo tracks, wherein each servo track comprises a plurality of servo sectors. A plurality of zones are defined, wherein each zone comprises a plurality of the servo tracks. A metric is generated for each zone, and when the metric for a first zone exceeds a first threshold, feedback compensation values for at least two servo tracks are generated, wherein the feedback compensation values compensate for a written-in error of the servo sectors of each servo track. When the metric for a second zone does not exceed the first threshold, generating feedback compensation values for the second zone is skipped.

Abstract: A disk drive is disclosed comprising a disk, a head, and control circuitry comprising a servo control system operable to actuate the head over the disk. A plurality of disturbance signals is generated in response to a vibration. A plurality of correlations is generated in response to each disturbance signal and an error signal of the servo control system. At least one of the disturbance signals is selected in response to the correlations. A feed-forward compensation value is generated in response to the selected disturbance signal, and the feed-forward compensation value is applied to the servo control system to compensate for the vibration.

Abstract: A disk drive is disclosed comprising a disk comprising servo data, and a head actuated over the disk. An offset r0 representing a difference between an axial rotation of the disk and an axial rotation of the servo data is estimated, and radial dependent timing compensation values are generated in response to the estimated r0. A phase error is generated in response to the servo data, and a control signal is generated in response to the phase error and the radial dependent timing compensation values. A frequency of an oscillator is adjusted in response to the control signal.

Abstract: A disk drive is disclosed comprising a head actuated over a disk comprising a plurality of spiral tracks, wherein each spiral track comprising a high frequency signal interrupted at a predetermined interval by a sync mark. An offset r0 representing a difference between an axial rotation of the disk and an axial rotation of the spiral tracks is estimated. Radial dependent timing compensation values are generated in response to the estimated r0. A phase error is generated in response to the sync marks in the spiral track crossings. A control signal is generated in response to the phase error and the radial dependent timing compensation values, and a frequency of an oscillator is adjusted in response to the control signal.

Abstract: A disk drive is disclosed comprising a disk comprising servo data, and a head actuated over the disk. An offset r0 representing a difference between an axial rotation of the disk and an axial rotation of the servo data is estimated, and radial dependent timing compensation values are generated in response to the estimated r0. A phase error is generated in response to the servo data, and a control signal is generated in response to the phase error and the radial dependent timing compensation values. A frequency of an oscillator is adjusted in response to the control signal.

Abstract: A disk drive is disclosed comprising a disk comprising a plurality of servo tracks defined by servo sectors, wherein each servo sector comprises servo data and a servo compensation value. While servoing a head over a target data track during a write operation, a position error signal (PES) is generated at each servo sector based at least in part on the servo data. When the servo compensation value of a first servo sector is recoverable, the write operation is aborted when the PES generated at the first servo sector exceeds a first write unsafe threshold. When the servo compensation value of the first servo sector is unrecoverable, the write operation is aborted when the PES generated at the first servo sector exceeds a second write unsafe threshold less than the first write unsafe threshold.

Abstract: A disk drive is described that uses a vibration sensor to generate a compensating feed-forward control signal to synchronize the write clock frequency with the modulated data island frequency. A linear vibration sensor is positioned with its sensitivity axis aligned with the tangential direction of a track at the radial position of the write head. The tangential component of the external linear vibration is measured by the sensor. The feed-forward control signal derived from the linear vibration sensor modifies the control voltage input to VCO (voltage controlled oscillator) in the write clock generator to adjust the write clock frequency to compensate for the modulated data island frequency caused by the tangential component of the linear vibration.

Abstract: A method and computer program product identify the location of a bad block on a disk platter of a hard disk drive, determine an avoidance area extending from the bad block, and prevent data from being written to the avoidance area.

Abstract: A disk drive comprises a track follow control system having a plurality of selectable frequency modes, the track follow control system configured to receive a position error signal and to output a control signal based on the position error signal, wherein the control signal is used by a head assembly to position a head over a disk. The disk drive also comprises a state estimator configured to receive the control signal and a position signal indicating a position of the head, to estimate a disturbance based on the control signal and the position signal, and to output an estimated disturbance signal based on the estimated disturbance. The disk drive further comprises a disturbance evaluator configured to receive the estimated disturbance signal, and to select one of the frequency modes of the track follow control system based on the estimated disturbance signal.

Abstract: A data storage device is disclosed comprising a disk comprising at least one servo seed pattern, and a head actuated over the disk. An amplitude measurement is generated based on a read signal emanating from the head while reading the disk. A number of times the amplitude measurement exceeds a first threshold is first counted during a first revolution of the disk, and a number of times the amplitude measurement exceeds the first threshold is second counted during a second revolution of the disk. The servo seed pattern is detected based on the first count and the second count.

Abstract: A disk drive is disclosed wherein a radial offset is measured between a first head and a second head at a plurality of points along a circumference of a corresponding first and second disk surface to generate a first plurality of radial offsets. A first radial offset is determined and a second radial offset is determined based on the first plurality of radial offsets, wherein the first radial offset corresponds to approximately a maximum in the first plurality of radial offsets and the second radial offset corresponds to approximately a minimum in the first plurality of radial offsets. A plurality of access commands are stored in a command queue, and a rotational position optimization (RPO) algorithm is executed to select a next access command to execute from the command queue, wherein the RPO algorithm is responsive to the first and second radial offsets.

Abstract: According to one embodiment, a disk storage apparatus includes a read controller and a servo controller. The read controller contains a combined position generator including a state observer and a combined position calculator. The servo controller controls a seek operation of the head based on the combined position. The servo controller stores the servo information in a memory and determines an occurrence of a state offset as an error between an actual position of the head and the combined position. The servo controller corrects the predicted position by the state observer based on the servo information stored in the memory and the combined position when the occurrence of the state offset is detected.

Abstract: A method or apparatus for changing a performance level of a disk drive from an initial performance level to a target performance level, wherein the disk drive includes a profile table. The method including determining an initial performance level, determining a target performance level, determining constant offset values that cause the performance level of the disk drive to match the target performance level, and programming a constant offset table of the profile table with the constant offset values.

Abstract: A disk drive is disclosed comprising a first disk surface comprising a plurality of tracks, wherein each track comprises a number of data sectors and a number of servo sectors, and a second disk surface comprising a plurality of tracks, wherein each track comprises a number of data sectors and a number of servo sectors. A first repeatable runout (RRO) sinusoid is generated representing an RRO of the first disk surface, and a second RRO sinusoid is generated representing an RRO of the second disk surface. A plurality of access commands are received from a host which are stored in a command queue, and one of the access commands is selected to execute in response to the first and second RRO sinusoids.

Abstract: A disk drive is disclosed comprising a head actuated over a disk comprising a plurality of servo tracks defined by servo sectors. The head is positioned over a first servo track, and a first position error signal (PES) by reading a first servo sector during a first revolution of the disk and in response to a first compensation value. A second compensation value is updated for a second servo sector based on the first PES during the first revolution of the disk. A second PES is generated by reading the second servo sector during the first revolution of the disk and in response to the updated second compensation value. The first compensation value is updated for the first servo sector based on the second PES during the first revolution of the disk. The head is actuated over the disk in response to the first PES and the second PES.

Abstract: A disk drive is disclosed comprising a head actuated over a disk comprising a plurality of non-circular servo tracks for defining a plurality of substantially circular tracks. Each non-circular servo track comprises a plurality of servo sectors defining a plurality of servo wedges. The head is positioned at a first offset relative to a first circular track and a relationship of servo bursts for each servo wedge is first generated. The head is positioned at a second offset relative to the first circular track and the relationship of the servo bursts for each servo wedge is second generated. For each servo wedge, a selection is made between the first generated relationship at the first offset and the second generated relationship at the second offset, and the servo bursts at the selected offset are evaluated to generate a track squeeze indicator.

Abstract: A disk drive is disclosed comprising a disk, a head, and control circuitry comprising a servo control system operable to actuate the head over the disk. A plurality of disturbance signals is generated in response to a vibration. A plurality of correlations is generated in response to each disturbance signal and an error signal of the servo control system. At least one of the disturbance signals is selected in response to the correlations. A feed-forward compensation value is generated in response to the selected disturbance signal, and the feed-forward compensation value is applied to the servo control system to compensate for the vibration.

Abstract: A disk drive is disclosed comprising a head actuated over a disk comprising a plurality of spiral tracks, each spiral track comprising a high frequency signal interrupted at a predetermined interval by a sync mark. The head is used to read the spiral tracks to generate a read signal representing spiral track crossings. A position error signal (PES) is generated in response to the spiral track crossings, and the head is servoed over the disk in response to the PES. Timing feed-forward compensation values are generated in response to the PES, and the timing feed-forward compensation values are used to open a demodulation window at each spiral track crossing, wherein the timing feed-forward compensation values compensate for a repeatable runout (RRO) of the spiral tracks.

Abstract: Methods and apparatus are provided for validating a detection of RRO address marks. After a potential RRO address mark is detected, a disclosed RROAM validation metric evaluates the energy of the remaining RRO data bits in the servo sector, relative to a predefined energy threshold. In addition, the number of remaining RRO data bits in the servo sector is compared to an expected value. The detected RRO address mark is validated in an exemplary embodiment if the RROAM validation metric satisfies the predefined energy threshold and the proper number of remaining RRO data bits is detected in the servo sector. The potential RRO address mark can optionally be discarded if the potential RRO address mark is not validated.

Abstract: A HDD comprising a temperature sensor disposed inside the HDD configured to periodically measure temperature inside of said hard disk drive; a magnetic disk; a read head; a write head; memory for storing RWO data. The RWO data is a function of a distance between the read head and the write head. The HDD also includes a RWO data adjustor configured to adjust the RWO data in response to a change in temperature of the HDD to compensate for a change in the distance between the read head and the write head based on the change in temperature.

Abstract: A magnetic head drive device including a suspension for supporting a magnetic head, and a main actuator that produces rotary movement of the magnetic head by applying current to a coil. The main actuator includes end arms each comprising a single micro-actuator, and an intermediate arm comprising two micro-actuators. The micro-actuators of the end arms are driven in the same direction, and the micro-actuators of the intermediate arm are driven in the opposite direction to the drive direction of the micro-actuators of said the arms.

Abstract: A disk drive is disclosed comprising a disk, a head actuated over the disk, and a controller. The disk comprises a plurality of data tracks and a plurality of servo wedges, wherein each servo wedge comprises a plurality of wedge repeatable runout (WRRO) fields in a circumferential direction, each of the plurality of WRRO fields including an WRRO compensation value for a different one of the data tracks and having a width that is wider than a width of the respective data track in a radial direction. The controller is configured to read the WRRO compensation value in at least one of the WRRO fields from the disk using the head, and to adjust a position of the head based on the read WRRO compensation value.

Abstract: A system includes a self-servo-write (SSW) module, a read module, and a write module. The SSW module writes servo spirals on a magnetic medium of a hard disk drive (HDD) via a write head of the HDD. The read module reads the servo spirals via a read head of the HDD and generates read signals. The write module writes non-servo data on the magnetic medium via the write head based on the read signals before the SSW module writes servo wedges on the magnetic medium.

Abstract: A disk drive is disclosed comprising head actuated over a disk comprising a reference pattern. The head is positioned at a first radial location, a first phase error is measured in response to the reference pattern at the first radial location, and a first repeatable runout (RRO) of the first phase error is measured. The head is positioned at a second radial location, a second phase error is measured in response to the reference pattern at the second radial location, and a second repeatable runout (RRO) of the second phase error is measured. The first and second RROs are processed to estimate an offset r0 representing a difference between an axial rotation of the disk and an axial rotation of the reference pattern.

Abstract: A method for reducing a disturbance associated with repeatable runout associated with a removable disc loaded into a storage system. The method includes, at the storage system: logically partitioning the removable disc into sectors; for each of the sectors, obtaining a corresponding profile of repeatable runout contained in the sector; and applying a runout control algorithm to each of the sectors to generate a repeatable runout control (RROC) waveform that is usable to suppress the repeatable runout in the sector as indicated by the profile corresponding to the sector. The method also includes, at the storage system: assembling each RROC waveform to generate a single RROC waveform that is useable to suppress repeatable runout as contained in an entire revolution of the removable disc; and storing, in a memory, the single RROC waveform.

Abstract: A management apparatus is described of a rotating motor and a load during power loss; the apparatus comprises a first switching circuit coupled with the rotating motor and a controller of said first switching circuit. The controller is configured to drive the first switching circuit so as to convert a back-electromotive force voltage developed in the rotating motor into a power supply voltage for the load. The first switching circuit is driven in accordance with a first duty cycle. The apparatus comprises a second switching circuit coupled with the load and driven in accordance with a second duty cycle. The controller is configured to vary said first and said second duty cycles to keep the power supply voltage for the load above or equal to a threshold voltage.

Abstract: A method is disclosed for adaptive learning of fundamental-frequency repeatable runout (1FRRO) compensation information in a disk drive. The disk drive includes a transducer head, a magnetic disk having a plurality of concentric data tracks defined by embedded servo wedges that provide position information, and a control system. In the method, 1FRRO compensation information is learned over a predetermined minimum number of disk revolutions. After the predetermined minimum number of disk revolutions, the 1FRRO compensation information is monitored for convergence while learning of the 1FRRO compensation information continues. Learning is terminated upon detection of convergence of the 1FRRO compensation information.

Abstract: Embodiments of the invention include data storage system with a servo system with a VGA feedback loop that corrects gain errors for servo bursts arising from track phase misalignment and difference in frequencies between AGC and servo bursts for seamed and seamless servo patterns. After the servo fields have been written as part of the manufacturing process, in one embodiment measurements of phase misalignment are made and recorded in nonvolatile memory for use during normal operation of the drive. One embodiment includes measuring misalignment using relative signal magnitudes from test bursts with various linear densities written in a data area during the self-servo writing process. In an alternative embodiment the measurements of phase misalignment can be made real-time during normal operation of the drive.

Abstract: A patterned-media magnetic recording disk drive has head positioning servo sectors on the disk that do not contain special patterns but merely use the same type of dots that are used for data. The “data” dots in angularly spaced sectors of the data tracks function as the servo sectors and are denoted as D-servo regions. The D-servo regions extend across an annular band of the disk, which may be a bootstrap band for self-servowriting. The dots in the annular band are randomly magnetized so that each track in each D-servo region provides a generally random readback signal at the data frequency. The precise radial and circumferential position of the read/write head within a D-servo region is determined by comparing the readback signal with a set of reference signal waveforms from a look-up reference table and finding the reference signal waveform that matches the readback signal.

Abstract: According to one embodiment, a magnetic disk includes a plurality of tracks each having a plurality of servo frames with servo burst data and repeatable runout correction data written thereto. The repeatable runout correction data includes a pattern repeated at a predetermined period and is written so that beginning of write is delayed by a time corresponding to a correction amount with respect to a base point corresponding to a synchronization timing position in the servo frame. A detector detects a phase delay amount corresponding to a time elapsed until the repeated pattern is read from the servo frame by a magnetic head, with respect to the synchronization timing position.

Abstract: According to one embodiment, a magnetic disk device includes: a magnetic disk having data spiral tracks extending from an outer circumference towards an inner circumference or from an inner circumference towards an outer circumference; a head configured to read data recorded in the data tracks of the magnetic disk that is rotating and to write data to the data tracks; and a controller configured to control the head to follow a predetermined data track in units obtained by subtracting a seek time required for the head to seek the predetermined data track from a rotation period.

Abstract: A method for positioning a magnetic-recording head. The method includes correcting amplitude of each burst signal of a plurality of burst signals read out with the magnetic-recording head from each respective burst pattern of a plurality of burst patterns. In addition, the method includes computing a deviation of the magnetic-recording head from a track based on corrected amplitudes of the plurality of burst signals. Moreover, the method includes positioning the magnetic-recording head on the track based on the deviation of the magnetic-recording head.

Abstract: A disk drive. The disk drive includes a head, an actuator, and a controller. The head accesses a disk. The actuator is configured to support the head and to move the head by action of a voice-coil motor in a substantially radial direction of the disk. The controller is also configured to perform servo control of the actuator by using servo data read out by the head. The controller includes at least one of a plurality of notch filters having a fixed center frequency inserted in a servo-control loop. The controller is configured to increase an attenuation rate by at least one of the plurality of notch filters having the fixed center frequency at a designated frequency, when a target position of the head is at a position selected from the group consisting of a position outside of a specified region and a position within the specified region.

Abstract: There is provided a content reproduction apparatus including a reproduction request receiving unit that receives from a first external device conforming to a first communication standard a request to reproduce content data selected by the first external device, a content data obtaining unit that obtains from a second external device conforming to the first communication standard, which stores the content data selected by the first external device, the content data in response to the received request, a content reproduction unit that reproduces the obtained content data, and a data converting unit that converts data which can be transmitted according to the first communication standard into data which can be transmitted according to a second communication standard different than the first communication standard.

Abstract: An apparatus can include a disk drive controller that includes at least one repeatable run out (RRO) compensator corresponding to a RRO component, the disk driver controller configured to change a head assembly position, and to disable the at least one RRO compensator in response to the head assembly position changing from one predetermined area of a disk to at least one other predetermined area of the disk

Abstract: According to one embodiment, a disk storage device includes: a disk on which a servo pattern is recorded; a head; a driver; a signal generator; a demodulator; and a controller. Position signals for detecting an offset position from a center of a track are recorded in a recording area of a servo pattern. The signal generator generates a first timing signal indicating a timing for reading the position signals. When the controller performs positional control along a virtual circular orbit of the disk, the signal generator generates a second timing signal. The period of the second timing signal for reading each of the position signals is made shorter than that of the first timing signal. A center time of the period of the second timing signal is shifted closer to a demodulation center time corresponding to a center of the recording area than that of the first timing signal.

Abstract: Embodiments of the present invention provide a servo write medium, method and device for writing servo information by self servo write on the servo region formed from a flat section of the discrete track medium. The recording or write device yields the same servo characteristics as magnetic servo writing, is superior to pre-patterned servo, and delivers a greater write storage capacity with an even higher recording density. According to one embodiment, a self servo write method is used to write servo information on a flat section formed on a patterned disk on which discrete tracks are formed. Timing detection patterns (grooves) required for controlling the timing along the periphery during self servo write are formed by pre-patterning on the disk, and RRO error signals used for positioning control along the radius are written in the servo information on a flat section of the disk.

Abstract: Methods, apparatuses, and systems implementing analog techniques to decode signals extracted from servo wedges of computer-readable storage media. A digital representation of at least a portion of a repeatable runout (RRO) signal derived from an analog signal read from a computer-readable storage medium is obtained. An estimate of a magnitude of the RRO signal is determined based on the digital representation. An error signal is generated to represent a difference between the estimate of the magnitude and a specified level of the magnitude of the RRO signal, and a gain value is configured, based on the error signal, for decoding a signal from the computer-readable storage medium.

Abstract: A method to compensate repeatable run out of a hard disk drive apparatus includes receiving a write or read command to write or read data with respect to a disk having an inner diameter (ID) area, a middle diameter (MD) area, and an outer diameter (OD) area which are preset, determining a present position of a magnetic head and a position where the magnetic head writes or read data, stopping an operation of at least one of RRO compensators for RRO components of particular frequencies when the present position of the magnetic head is the ID area and the position where the magnetic head writes or reads the data is the MD area or OD area of the disk, and performing data writing or reading by performing seeking and settling of the magnetic head.

Abstract: A storage system includes a first buffer configured to store a first repeatable runout profile (RRP) for a sector of a rotating storage medium. A second buffer is configured to store a second RRP for the sector. A controller: controls a servo of the rotating storage medium based on the first RRP during a first revolution of the rotating storage medium; and learns the second RRP (i) while operating in a track-following mode, and (ii) during the first revolution. The controller ceases learning of the second RRP when one of (i) the controller is operating in a seek mode and (ii) the rotating storage medium is in an off-track state. Subsequent to the first revolution of the rotating storage medium and based on whether the learning of the second RRP was stopped during the first revolution, the controller replaces the first RRP with the second RRP in the first buffer.

Abstract: A disk drive device is provided with a recording disk, a base member, a bearing unit, and a hub member. In a marking step, unbalance information indicating the displacement of the center of gravity of the hub member with respect to the rotation center of the hub member is acquired, and an information mark containing the unbalance information is applied to at least the hub member or the base member. In an installing and adjustment step, the unbalance information is read form the information mark, and the position for installing the recording disk in an outer cylinder part is determined in accordance with the unbalance information so as to install the recording disk on the hub member.

Abstract: According to one embodiment, a magnetic disk device includes a magnetic disk, a magnetic head, a position error signal output module, a vibration pattern detector, an adder, and a head positioning controller. The magnetic head moves over the magnetic disk. The position error signal output module outputs a position error signal based on a difference between a head position of the magnetic head over the magnetic disk and a target position on the magnetic disk. The vibration pattern detector detects a vibration pattern of the magnetic head caused by vibration. The adder adds the position error signal to an offset signal indicating amplitude of the vibration pattern. The head positioning controller moves the head position to the target position based on a result of addition by the adder.

Abstract: A disk drive is disclosed comprising a disk including a plurality of tracks, and a head actuated over the disk, wherein the head comprises a read element radial offset from a write element. A jog value corresponding to the radial offset is calibrated by writing data to a plurality of tracks, reading the plurality of written tracks to generate an actual track crossing signal, cross correlating the actual track crossing signal with an ideal track crossing signal to generate a cross correlation signal, and calibrating the jog value in response to the cross correlation signal.

Abstract: A disk drive is disclosed comprising a first disk surface comprising a plurality of tracks, wherein each track comprises a number of data sectors and a number of servo sectors, and a second disk surface comprising a plurality of tracks, wherein each track comprises a number of data sectors and a number of servo sectors. A first repeatable runout (RRO) sinusoid is generated representing an RRO of the first disk surface, and a second RRO sinusoid is generated representing an RRO of the second disk surface. A plurality of access commands are received from a host which are stored in a command queue, and one of the access commands is selected to execute in response to the first and second RRO sinusoids.