Abstract: A disk drive is disclosed wherein N data wedges of write data are buffered in a buffer. After writing at least two of the data wedges to the disk including a first data wedge and a second data wedge, a first servo metric value is measured when reading a first servo sector, and a second servo metric value is predicted based on the first servo metric value, wherein the second servo metric value corresponds to a second servo sector following the first servo sector. When the first servo metric value indicates a safe write condition and the second servo metric value indicates an unsafe write condition, the first data wedge is released from the buffer, and when the first servo metric value indicates a safe write condition and the second servo metric value indicates a safe write condition, the first and second data wedges are released from the buffer.

Abstract: A first portion of a track identifier is read from a first servo wedge of a track of a magnetic disk. A second portion of the track identifier is read from a second servo wedge of the track. The second portion includes least-significant bits of the track identifier that are also stored in the first portion. The first and second portions are combined to determine the track identifier for the first and second servo wedges, and the track is identified using the track identifier.

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: According to one embodiment, in a method for servo demodulation, a first demodulated signal and a second demodulated signal, which are calculated from amplitude values of burst signal patterns of a first area and a second area, are generated in order to generate a position error signal of a reader, based on a servo pattern read from a disk by the reader. Further, in the method for servo demodulation, a square-root of sum of squares of the first and the second demodulated signals is calculated, and an optimal compensation coefficient of a linearity correction function to be used in linearity compensation of the position error signal is calculated based on a maximum value and a minimum value of the square-root of sum of squares.

Abstract: A system, method, and apparatus for forming a high quality master pattern for patterned media, including features to support servo patterns, is disclosed. Block copolymer self-assembly is used to facilitate the formation of a track pattern with narrower tracks. E-beam lithography forms a chemical contrast pattern of concentric rings, where the spacing of the rings is equal to an integral multiple of the target track pitch. The rings include regions within each servo sector header where the rings are offset radially by a fraction of a track pitch. Self-assembly is performed to form a new ring pattern at the target track pitch on top of the chemical contrast pattern, including the radial offsets in the servo sector headers. When this pattern is transferred to disks via nanoimprinting and etching, it creates tracks separated by nonmagnetic grooves, with the grooves and tracks including the radial offset regions.

Abstract: A disk drive is disclosed comprising a head actuated over a disk comprising servo information. A position error signal is generated while executing a first plurality of seek operations to seek the head over a seek length, and first feed-forward compensation values are adapted for a first segment of the seek length using an iterative learning control algorithm based on the position error signal. During a second plurality of seeks, second feed-forward compensation values are adapted for a second segment of the seek length using the iterative learning control algorithm based on the position error signal. The servo control system is operable to execute the second plurality of seek operations using the first feed-forward compensation generated for the first segment of the seek length.

Abstract: A disk drive is disclosed comprising a head actuated over a disk. A position y of the head is measured based on servo sectors, and the measured position y of the head is adjusted based on: z1=y+c1(y) where z1 represents a first adjusted position and c1(y) represents first correction values. The first adjusted position z1 is adjusted based on: z2=z1+c2(z1) where z2 represents a second adjusted position and c2(z1) represents second correction values. The first and second correction values are combined based on: c3(y)=c1(y)+c2(y+c1(y)). The measured position y of the head is adjusted based on: z3=y+c3(y) where z3 represents a third adjusted position comprising the adjustment based on c1(y) and the adjustment based on c2(y), and c3(y) represents third correction values.

Abstract: A magnetic disk device includes a magnetic disk, a head and a control section. The head writes data to the magnetic disk. The control section controls the head to move along a virtual circular orbit of the magnetic disk that includes a first servo sector region and a second servo sector region. The second servo sector region has a larger servo interval than the first servo sector region, and stores a larger number of write bits than the first servo sector region.

Abstract: According to one embodiment, a magnetic head, a magnetic disk and a magnetic recording controller are provided. The magnetic disk has a burst pattern recorded thereon for determining a position of the magnetic head on a track based on a reading result by the magnetic head. The magnetic recording controller corrects a demodulation position of the magnetic head based on an offset correction value subject to fluctuation of the burst pattern.

Abstract: A method of writing servo data to a data storage medium includes reading a servo instruction from a memory, the servo instruction comprising a control portion and a data portion, processing the servo instruction in a controller to generate a servo data pattern from the data portion based on the control portion, and transferring the servo data pattern to the data storage medium. The processing may include transforming the data portion into the servo data pattern based on the control portion. The processing also may include following a command in the control portion to use the data portion as an index to retrieve a pre-programmed servo data pattern from a pattern store. The transferring may include storing the servo data pattern in a buffer, and writing the servo data pattern from the buffer to the data storage medium.

Abstract: A disk drive is disclosed comprising a disk comprising a plurality of data tracks defined by servo sectors. Each servo sector comprises a periodic preamble recorded at a first frequency, servo data, a periodic reference pattern recorded at a second frequency different from the first frequency, and at least one servo burst. A servo sector is processed by processing the periodic preamble to extract the servo data, demodulating the servo burst in response to the periodic reference pattern, generating a position error signal based on the extracted servo data and the demodulated servo burst, and measuring a fly height of the head based on the periodic reference pattern.

Abstract: According to one embodiment, a head position detecting method and a magnetic disk device includes measuring a burst output by reading a burst pattern, which is recorded on a magnetic disk, with a magnetic head and calculating a demodulation position of the magnetic head on the basis of the result of the correction of the phase shift of the burst output corresponding to magnetization transition curvature of the burst pattern.

Abstract: A servo control field on a recordable medium includes a bit patterned media (BPM) pattern including a plurality of dots arranged in a down-track orientation and in a cross-track orientation, wherein the dots comprise a plurality of dot composites. Each of the dot composites includes a plurality of dots. A first spacing between adjacent ones of the plurality of dots in a dot composite in the down-track direction on the recordable medium is less than a second spacing between adjacent ones of the plurality of dot composites in the down-track direction. A readback signal generated in response to the BPM patterned may be filtered to attenuate harmonic frequencies in the readback signal.

Abstract: According to one embodiment, a magnetic disk drive includes a disk and a controller. The disk includes a plurality of zones each having a plurality of tracks. The disk is formatted such that a plurality of servo frames are discretely recorded in each of the plurality of tracks. The plurality of servo frames include servo preamble data of a second length which corresponds to the zone having the track and which is less than or equal to a first length serving as a reference. The controller allows a head to read the servo frames from the disk via a read amplifier.

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 disk drive is disclosed comprising a head and a disk comprising a plurality of servo tracks, wherein each servo track comprises a plurality of servo sectors. The disk drive further comprises control circuitry comprising a servo control system operable to actuate the head over the disk in response to the servo sectors. The disk is rotated at a first speed and the servo sectors are read at a first servo sample frequency to generate first servo samples. The disk is rotated at a second speed different from the first speed and the servo sectors are read at a second servo sample frequency to generate second servo samples. The second servo samples are processed to measure a frequency response of the servo control system proximate the first servo sample frequency.

Abstract: A method for recording data to a magnetic media while simultaneously reading sync and or servo data with reduced noise from the write head affecting the reading of the sync and or servo data. The invention records data using a write head of a first slider and reads the sync and or servo data from a read head located on a different slider that is facing a different disk surface than the first slider. In this way, magnetic or thermal noise from the write head does not affect the reading of the sync and or servo data.

Abstract: Disk drives are described that include a hybrid servo patterns in which the augmented servo burst fields, which can be Integrated Servo sequences, that provide the PES and also supply additional information such as a SAM, LSBs of the track identifier (TID), sector number, depending on the specific embodiment. Embodiments without write-to-read gaps before the servo sector SIDs are described. The augmented servo burst fields can be read after gapless writing of the preceding data area. For seeking operations the needed bits of the TID without having to detect or decode the Integrated Servo sequences or other augmented servo burst fields. Depending on the embodiment all or the most significant bits of the track identifier can be obtained during seeks by reading the TID fields passing under a read head as the read head moves across tracks without having to detect or decode the Integrated Servo sequences.

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 vibration signal VS(k) is measured representing a disturbance in the servo control system. A first future value of the vibration signal VS(k) is predicted based on: VS1(k+1)=?1[VS(k)?VS(k?1)]+VS(k) where ?1 is a first scalar corresponding to a first frequency range. A second future value of the vibration signal VS(k) is predicted based on: VS2(k+1)=?2[VS(k)?VS(k?1)]+VS(k) where ?2 is a second scalar corresponding to a second frequency range different from the first frequency range.

Abstract: Disk drives are described that include a hybrid servo patterns in which the augmented servo burst fields, which can be Integrated Servo sequences, that provide the PES and also supply additional information such as a SAM, LSBs of the track identifier (TID), sector number, depending on the specific embodiment. Embodiments without write-to-read gaps before the servo sector SIDs are described. The augmented servo burst fields can be read after gapless writing of the preceding data area. For seeking operations the needed bits of the TID without having to detect or decode the Integrated Servo sequences or other augmented servo burst fields. Depending on the embodiment all or the most significant bits of the track identifier can be obtained during seeks by reading the TID fields passing under a read head as the read head moves across tracks without having to detect or decode the Integrated Servo sequences.

Abstract: A servo writer is disclosed operable to write servo sectors on a disk to define non-circular servo tracks. The servo writer comprises control circuitry including a servo control system operable to measure a position of a head over the disk to generate a position signal, generate a position error signal (PES) representing a difference between the position signal and a reference signal, process the PES with a servo compensator to generate a control signal, and position the head over the disk in response to the control signal. A disturbance is induced into the servo control system, and while positioning the head over the disk in response to the control signal, a plurality of servo sectors are written on the disk to define a servo track, wherein the disturbance induced into the servo control system causes the servo track to be non-circular relative to a rotation axis of the disk.

Abstract: A disk drive is described with a single servo master timer that is used to control timing critical signals such as servo gate, SAM windows, channel power save, PREAMP power save and so on. The master timer is adjusted to compensate for SAM detection errors (early, late or missed) and provides improved servo timing quality. In an embodiment the adjustable master timer can be selectably clocked by either the DLC/DSW clock or the system clock.

Abstract: An extended servo mark word is used when an error is detected from a servo mark. For example, a servo mark associated with a disk drive track may be detected during a data access operation. In response to an error in detecting the servo mark, at least one adjacent bit is evaluated together with the servo address mark to overcome the error.

Abstract: Embodiments described herein provide for robust servo patterns that comply with planarization constraints and also allow use of a single master template for manufacture of both the front and back of a magnetic disk. Planarization constraints are met because only a portion of servo data is hard patterned on the magnetic disk and the hard patterned servo data areas comply with planarization constraints. The servo pattern has two symmetrical servo write assist patterns, one on each side of a central burst pattern. The servo sync, SAM, track-ID, sector-ID, and/or RRO values can be written magnetically by the write head onto these servo write assist patterns after the completion of the planarization process. The symmetric design of the servo pattern allows both a left-to-right and a right-to-left servo write and read back, thereby enabling use of a single master template in magnetic disk manufacture.

Abstract: A magnetic recording disk has nondata regions that contain a group of first nondata islands with one area and a magnetization in one perpendicular direction, and a group of second nondata islands with a smaller area and a magnetization in the opposite direction. To magnetize the nondata islands with the proper magnetization directions, a DC magnetic field much greater than the coercive field of the magnetic recording layer is applied in one direction to the entire disk to magnetize all of the nondata islands in the same direction. Then the disk is heated to a predetermined temperature, and while the disk is at this temperature, a second DC magnetic field less than the first DC magnetic field is applied for a predetermined time in the opposite direction to the entire disk. This reverses the magnetization direction of the smaller islands without switching the magnetization of the larger islands.

Abstract: A disk drive comprising a head for accessing a disk, an actuator for moving the head in the radial direction of the disk and a controller. The controller for servo control of the actuator based on servo data read out from the disk by the head. The controller is configured for maintaining a width of the adaptive chasing notch filter below a specified value in servo system control and estimating an oscillation frequency of the actuator.

Abstract: A magnetic storage medium comprises a plurality of discrete magnetic elements and first and second adjoining servo sectors. Each of the servo sectors comprises first and second rows of the discrete magnetic elements extending in a track direction. The second row of the discrete magnetic elements are stacked relative to the discrete magnetic elements of the first row in a cross-track direction that is perpendicular to the track direction. The discrete magnetic elements of the first servo sector are staggered in the cross-track direction relative to the discrete magnetic elements of the second servo sector.

Abstract: A given reference pattern is written on bit patterned media that has an initial reference pattern already disposed thereon. A write phase and frequency is detected based on the initial reference pattern and the given reference pattern is written on the bit patterned media at the detected write phase and frequency.

Abstract: A bit patterned recording system includes a servo channel module configured to recover servo fields written with servo information. A field locator module is configured to locate a field printed to data islands of a medium based on a location of one of the servo fields. The servo islands and the data islands have different spacing. A servo clock has a different phase and frequency than a data clock. A phase error calculator module is configured to estimate a phase error of the data clock based on the field and the data clock. The phase error is used to adjust a phase of the data clock.

Abstract: A disk drive is disclosed comprising a head actuated over a disk, the disk comprising a plurality of servo sectors defining a plurality of servo tracks, wherein the servo tracks form a plurality of servo zones. A servo data rate of servo sectors in a first servo zone is different than a servo data rate of servo sectors in a second servo zone. A boundary of a first servo zone overlaps with a boundary of a second servo zone over a transition zone. The servo sectors of the first servo zone are interleaved with the servo sectors of the second servo zone within the transition zone. At least one servo parameter is adjusted when the head is over the transition zone in order to transition between the first servo zone and the second servo zone.

Abstract: Disk drives are described in which the conventional write-to-read gap is omitted in selected sectors which frees up space that can be used for other purposes including writing a higher number of bits in the user data area in the gapless selected sectors. Alternative embodiments can use the additional space for servo information such as a repeatable run out (RRO) field. Conventional servo sector SID formats can be used for both gapped and gapless SIDs, which means that during seeking and reading operations full SIDs can be read for every wedge. The tradeoff for being able to write data much closer to the gapless SIDs is that the servo system does not detect the SAM or read the TID in the gapless SIDs during write operations.

Abstract: A disk drive is disclosed comprising a disk comprising a plurality of servo tracks defined by servo sectors. The disk drive further comprises a head comprising a read element offset linearly from a write element by a gap such that when the disk rotates, the read element reaches a servo sector before the write element. During a first operation, a first length of a beginning of the servo sector is read, and during a write operation, a second length of the beginning of the servo sector shorter than the first length is read to enable data to be written while the read element is over at least part of the servo sector.

Abstract: The present disclosure describes systems and methods for controlling synchronization of a servo clock by tying the triggering of the gate signal of the position error signal field of the short servo wedge portion directly to the synchronization marker in the full servo wedge. The systems and methods described herein include controlling synchronization of a servo clock for reading servo information from a disk that is rotating relative to a read head. The systems and methods may include estimating a gate delay corresponding to a position error signal (PES) field in a short null servo wedge based, at least in part, on the location of the servo synchronization marker. The systems and methods include producing a servo clock timing control signal based on the estimated gate delay, and applying the servo clock timing control signal to the servo clock.

Abstract: In a disk storage system, the disk may include a full null servo position error signal (“PES”) wedge, followed by a data wedge, and then a short null servo PES wedge. To improve the accuracy with which information read from the short null servo PES wedge can be used to help keep the read head centered over the information track being read, the short null servo PES wedge may include a calibration field. Information read from the calibration field can be used to compensate the subsequently read PES information in the short wedge for possible sampling phase error that may have accumulated since the full null servo PES wedge was read. This type of short null servo PES wedge also has other possible uses.

Abstract: Techniques are provided for performing bit-locked operations on media. A first control signal is received from a first source, and a second control signal is generated at a second source in response to receiving the first control signal. The media is accessed according to the second control signal. One or more synchronization markers are located during the accessing of the media, and bit-level synchronization between the second source and the media is achieved based, at least partially, on the one or more synchronization markers. A control operation is performed on the media with bit-level synchrony between the second source and the media.

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: The present inventions are related to systems and methods for transferring information to and from a storage medium, and more particularly to systems and methods for positioning a sensor in relation to a storage medium. For example, an apparatus for determining a sensor position is disclosed that includes a data stream processor operable to generate a number of data streams at different frequencies based on an input data stream, a number of servo preamble detectors each operable to process a different one of the data streams to detect a servo preamble, a selector operable to output one of the data streams in which the servo preamble was detected as a winning data stream, and a pattern detector operable to detect a pattern in the winning data stream.

Abstract: According to one embodiment, there is provided an information recording device that records information on a magnetic disk using a magnetic head. The registering module registers position data of a temporary defective sector using a sector where an off-track has occurred as a temporary defective sector. The reading module reads data from a target track. The cancellation processing module performs inter-track interference component cancellation processing with respect to the data read by the reading module using data written to a track adjacent to the target track, in which when a sector adjacent to a processing target sector in a track width direction is a temporary defective sector registered in the registering module, inter-track interference component cancellation processing is performed using data written to a substitute sector corresponding to the registered temporary defective sector.

Abstract: Embodiments described herein provide for robust servo patterns that comply with planarization constraints and also allow use of a single master template for manufacture of both the front and back of a magnetic disk. Planarization constraints are met because only a portion of servo data is hard patterned on the magnetic disk and the hard patterned servo data areas comply with planarization constraints. The servo pattern has two symmetrical servo write assist patterns, one on each side of a central burst pattern. The servo sync, SAM, track-ID, sector-ID, and/or RRO values can be written magnetically by the write head onto these servo write assist patterns after the completion of the planarization process. The symmetric design of the servo pattern allows both a left-to-right and a right-to-left servo write and read back, thereby enabling use of a single master template in magnetic disk manufacture.

Abstract: Various embodiments of the present invention provide systems and methods for data processing. As an example, a data processing circuit is disclosed that includes a codeword detector circuit operable to apply a codeword based data detection algorithm to a data input corresponding to an encoded servo data region to yield a detected output, and a servo address mark processing circuit operable to identify a pre-defined pattern in the detected output.

Abstract: A data storage device with improved data storage densities, coupled with lower hard error and write-inhibit events is described. A feed-forward write inhibit (FFWI) method enables data tracks to be written more densely. Alternatively, the FFWI method may reduce the hard error and write inhibit events to improve data storage performance. A concept of virtual tracks enables the FFWI method to be applied to the writing of circular data tracks with non-circular servo tracks, or to the writing of non-circular data tracks with PES data from circular servo tracks—in both cases, improvements to performance and/or storage densities are enabled. The FFWI method may also be applied to the case of both non-circular servo and data tracks.

Abstract: The present disclosure includes systems and techniques relating to control of magnetic recording devices, such as disk drives. Systems and techniques include generating timing data based on a waveform produced by a head operated with respect to a magnetic rotating recording medium; operating a model-based predictor based on model parameters to produce one or more model-based predictor outputs to compensate for deterministic disturbances in an area situated on a portion of a track on the recording medium; operating a stochastic predictor based on the timing data to produce one or more stochastic predictor outputs to compensate for nondeterministic disturbances in the area; and performing one or more clock frequency adjustments that are responsive to the head being operated within the area, the one or more clock frequency adjustments being based on the one or more model-based predictor outputs and the one or more stochastic predictor outputs.

Abstract: Embodiments described herein provide for patterned media concentric zones with an alternating series of concentric servo zones and overlap zones. The overlap zones facilitate the writing of servo data between servo zones of different servo frequency. The overlap zones may be dual frequency zones. The dual frequency zones have a first set of overlap patterns with the substantially identical pattern as the bordering lower frequency servo zone and a second set of overlap patterns with the substantially identical pattern as the bordering higher frequency servo zone. A bootstrap zone can be included near the inner diameter to assist initial servo writing. Alternatively the overlap zones are bootstrap zones. Such bootstrap zones have both bootstrap patterns and overlap patterns, the overlap patterns have the substantially identical pattern as a bordering servo zone. Bootstrap patterns only require DC magnetization for servo operability.

Abstract: A method of self servo-writing servo information to a plurality of disk surfaces in a disk drive that includes writing servo information to a plurality of disk surfaces in a first direction, writing servo information to a plurality of disk surfaces in a second direction, and determining an amount of overlap to be written on a reference surface with the reference head that will produce an overlap of servo information on each of the surfaces in the disk drive to which servo information is to be written. The method also includes switching to different tables when seeking across the overlap or border areas.

Abstract: Embodiments described herein provide for patterned media concentric zones with an alternating series of concentric servo zones and overlap zones. The overlap zones facilitate the writing of servo data between servo zones of different servo frequency. The overlap zones may be dual frequency zones. The dual frequency zones have a first set of overlap patterns with the substantially identical pattern as the bordering lower frequency servo zone and a second set of overlap patterns with the substantially identical pattern as the bordering higher frequency servo zone. A bootstrap zone can be included near the inner diameter to assist initial servo writing. Alternatively the overlap zones are bootstrap zones. Such bootstrap zones have both bootstrap patterns and overlap patterns, the overlap patterns have the substantially identical pattern as a bordering servo zone. Bootstrap patterns only require DC magnetization for servo operability.

Abstract: The present inventions are related to systems and methods for transferring information to and from a storage medium, and more particularly to systems and methods for positioning a sensor in relation to a storage medium. For example, an apparatus for determining a sensor position is disclosed that includes discrete Fourier transform calculators operable to process input data to yield a magnitude response of the input data at each of a number of candidate frequencies, a comparator operable to compare the magnitude responses to yield a winning candidate frequency, a servo controller operable to process at least one servo field in the input data to identify a position of a sensor based on the at least one servo field, and a servo frequency synthesizer operable to establish a frequency of operation in the servo controller based at least in part on the winning candidate frequency.

Abstract: Embodiments described herein provide for patterned media concentric zones with an alternating series of concentric servo zones and overlap zones. The overlap zones facilitate the writing of servo data between servo zones of different servo frequency. The overlap zones may be dual frequency zones. The dual frequency zones have a first set of overlap patterns with the substantially identical pattern as the bordering lower frequency servo zone and a second set of overlap patterns with the substantially identical pattern as the bordering higher frequency servo zone. A bootstrap zone can be included near the inner diameter to assist initial servo writing. Alternatively the overlap zones are bootstrap zones. Such bootstrap zones have both bootstrap patterns and overlap patterns, the overlap patterns have the substantially identical pattern as a bordering servo zone. Bootstrap patterns only require DC magnetization for servo operability.

Abstract: A disk drive is disclosed comprising a disk including a plurality of sectors each comprising a sector sync mark pattern and sector data preceding and following the sector sync mark pattern, and a head actuated over the disk for generating a read signal. A data sequence is detected from the read signal, and the data sequence is correlated with an extended sync mark comprising a target sync mark pattern and target data. The correlation of the target sync mark pattern with the data sequence is biased relative to the correlation of the target data with the data sequence.

Abstract: Embodiments described herein include systems and methods for correcting for errors caused by disturbances to disk drives, such as disturbances due to shocks or vibrations incident on the drive. For example, systems and methods described herein advantageously correct for corruption to current data as well as previously written. Data may be rewritten in the current track that was being written to when the disturbance occurred, and may also be rewritten to one or more nearby previously written tracks, such as one or more adjacent tracks. According to some aspects, the direction of head deviation is used to select the appropriate corrective action.

Abstract: In an optical tape drive having optical heads for writing data in tracks on an optical tape, each track having an off-track threshold, a system and method are disclosed for off-track write prevention. The system includes multiple actuators, each actuator configured to control a position of an associated optical heads. The system also includes a controller configured to determine a position of each of the optical heads relative to an associated track on the optical tape and to prevent, in response to an event causing an optical heads to have a position outside the off-track threshold of the associated track, only that optical head from writing data to the optical tape and to buffer a stream of data for that optical head for later processing.