Abstract: Provided is a method, computer program product, and system for handling seek commands for a tape drive. The method includes receiving a seek command for moving tape in the tape drive to a target position. The method further includes determining whether to move the tape according to a first procedure or a second procedure. The first procedure includes directly moving the tape from the current position to the target position with the tape at the first tension. The second procedure includes moving the tape from the current position to the HWM with the tape at the first tension and moving the tape from the HWM to the target position with the tape at the second tension. The method further includes moving the tape according to the determined first or second procedure.

Abstract: A hard disk drive or other storage device comprises a storage medium, a read/write head, and read channel circuitry coupled to the read/write head. The read channel circuitry comprises a despreader configured to generate a stitched logic sector by stitching together subsectors of that logic sector that were interleaved with subsectors of other logic sectors for storage on the storage medium, and a subsector bridging control module configured to control a number of bridging bits inserted by the despreader between a given pair of adjacent subsectors of the stitched logic sector. The subsector bridging control module may be illustratively configured to cause the despreader to insert a sufficient number of bridging bits between each pair of adjacent subsectors of the stitched logic sector so as to prevent discontinuities that might otherwise arise from use of X-averaging in generation of Y samples from X samples in a retry mode of operation.

Abstract: A data storage device is disclosed comprising a head actuated over a disk. A plurality of data tracks on the disk are first written, and a metric representing a spacing between at least two of the first written data tracks is generated. At least two of the plurality of data tracks are rewritten based on the generated metric such that the rewritten data tracks comprise a more equal spacing compared to the first written data tracks.

Abstract: High performance is obtained without preventing achievement of a target read data rate. In a controller 16 of a tape drive, a command processing unit 41 receives a synchronization command, and a buffer management unit 42 passes data in a buffer to a channel input-output unit 43. Then, upon completion of writing the data to the tape, a backhitch determination unit 44 determines whether or not to execute backhitch. If it is determined that backhitch should be skipped, the speed determination unit 46 determines a tape speed that minimizes a sum of a time required to write data without backhitch within a range where a data amount of a monitor target is to be written in order to achieve a target read data rate, and a time required to write data with backhitch within the range. Then, an operation signal output unit 49 issues an instruction to change the tape speed to the determined tape speed after execution of backhitch.

Abstract: Data of a target capacity calculated by a nominal capacity of a tape medium minus a data capacity lost due to execution of backhitchless writing is written to the tape medium. In a tape drive, a command processing unit 41 receives a synchronization command, and a buffer management unit passes data in a buffer to a channel input-output unit. Upon completion of writing the data to the tape, a backhitch determination unit determines whether a mode information storage unit stores information indicating that a high data rate mode is on, whether data of a target capacity can be written to the tape, and whether the written data can be read at a target read data rate. An operation signal output unit issues a command to execute backhitch in case these conditions are not satisfied.

Abstract: A shingled magnetic recording hard disk drive that uses writeable cache tracks in the inter-band gaps between the annular data bands minimizes the effect of far track erasure (FTE) in the boundary regions of annular data bands caused by writing to the cache tracks. Based on the relative FTE effect for all the tracks in a range of tracks of the cache track being written, a count increment (CI) table or a cumulative count increment (CCI) table is maintained. For every writing to a cache track, a count for each track in an adjacent boundary region, or a cumulative count for each adjacent boundary region, is increased. When the count value for a track, or the cumulative count for a boundary region, reaches a predetermined threshold the data is read from that band and rewritten to the same band.

Abstract: A heat-assisted magnetic recording (HAMR) disk drive has a laser, a transducer coupled to the laser and a rotatable disk. The disk has a recording layer with concentric or spiral data tracks, servo sectors extending across the tracks, a laser power gap adjacent each servo sector, and data sectors between the laser power gaps and the servo sectors. The servo sector preceding the first data sector to be written and the servo sector following the last data sector to be written are identified. Any old data in the data sectors between said first and last servo sectors is acquired, and the old and new data is combined. The laser is turned on when the laser power gap adjacent the first servo sector rotates past the transducer. The combined old and new data is then written in all of the data sectors continuously between said first and last servo sectors.

Abstract: According to one embodiment, there is provided a method of temporarily storing data in a buffer. The method determines whether data written based on sequential writing is of a first type or a second type in data type. The method stores the written data in association with the determined data type in the buffer. The method further controls the buffer so that the data of the first type stored in the buffer may be held in the buffer for a length of time twice as long as time T1 corresponding to one revolution of a disk and the data of the second type stored in the buffer may be held in the buffer for the time T1.

Abstract: Described embodiments cancel inter-track interference (ITI) from one or more sectors read from a desired track of a storage medium. A read channel reads one or more sectors in the desired track and generates one or more groups of sample values corresponding to each of the sectors. An ITI canceller estimates an ITI response and an ITI signal for each sample value corresponding to (i) a next adjacent track and (ii) a previous adjacent track. If the estimated ITI response of the previous adjacent track reaches a predetermined threshold, the ITI canceller subtracts the estimated ITI signal corresponding to the previous adjacent track from each associated sample value of the desired track. If the estimated ITI response of the next adjacent track reaches a predetermined threshold, the ITI canceller subtracts the estimated ITI signal corresponding to the next adjacent track from each associated sample value of the desired track.

Abstract: Various embodiments of the present invention provide systems and methods for data processing. As an example, a data processing circuit is discussed that includes an inter-track interference determination circuit operable to calculate an inter-track interference from a previous track data set based at least in part on the previous track data set and a current track data set. The previous track data set includes a gap. A portion of the data in the previous track data set corresponds to a previous track on a storage medium, and the data in the previous track data set corresponding to the gap corresponds to a track preceding a previous track.

Abstract: A disk drive is disclosed comprising a head actuated over a disk comprising a plurality of servo sectors defining a plurality of servo tracks. The servo tracks form a plurality of servo zones. A disk locked clock is synchronized relative to a servo data rate of the servo zone the head is over. A first reader/writer gap is measured in cycles of the disk locked clock at a first servo track in the first servo zone. A second reader/writer gap is measured in cycles of the disk locked clock at a second servo track in the second servo zone. The first and second reader/writer gaps are normalized to generate a normalized first and second reader/writer gaps. A third reader/writer gap is estimated in cycles of the disk locked clock at a third servo track in the second servo zone based on the normalized first and second reader/writer gaps.

Abstract: Injecting pad bits during a read operation to improve format efficiency is disclosed. In some embodiments, a pad sequence associated with error correction is not stored in a sector on a disk. Instead, the pad sequence is merged at a read channel with data stored in a sector that is accessed by the read channel.

Abstract: A shingled magnetic recording (SMR) hard disk drive (HDD) essentially eliminates the effect of far track erasure (FTE) in the boundary regions of annular data bands caused by writing in the boundary regions of adjacent annular data bands. The extent of the FTE effect is determined for each track within a range of tracks of the track being written. Based on the relative FTE effect for all the tracks in the range, a count increment (CI) table or a cumulative count increment (CCI) table is maintained for all the tracks in the range. For every writing to a track in a boundary region, a count for each track in an adjacent boundary region, or a cumulative count for the adjacent boundary region, is increased. When the count reaches a predetermined threshold the data is read from that band and rewritten to the same band.

Abstract: Systems and techniques to interpret signals on a noisy channel. A described system includes a filter, buffer, detector, controller, and averager. The buffer can store a group of signals, including a filtered digital signal and previous signal(s). The controller can determine whether first discrete values are adequately indicated and initiate a retry mode when the first discrete values are not adequately indicated. The averager can produce a new signal, in the retry mode, based on an average of at least a portion of the group of signals. The detector can interpret the new signal as second discrete values. The controller can determine whether the second discrete values are adequately indicated based on a measurement of differences between hard decisions indicated by the new signal and hard decisions indicated by the filtered digital signal. The controller can selectively exclude a signal of the group of signals from the average.

Abstract: A thin film magnetic recording head is fabricated by forming a substrate from opposing ferrite blocks which have a ceramic member bonded between them. This structure is then diced to form a plurality of columns, wherein each column has a ferrite/ceramic combination. Each column represents a single channel in the completed head. A block of ceramic is then cut to match the columned structure and the two are bonded together. The bonded structure is then cut or ground until a head is formed, having ceramic disposed between each channel. A ferrite back-gap is then added to each channel, minimizing the reluctance of the flux path. The thin film is patterned on the head to optimize various channel configurations.

Abstract: Methods and apparatus are provided for measuring servo address mark distance in a read channel using selective fine phase estimates. A distance between servo address marks (SAMs) in servo data of a magnetic recording media can be computed by obtaining a count of a number of time intervals between SAM patterns; obtaining a plurality of fractional phase estimates; selecting at least one of the plurality of fractional phase estimates as a selected fractional phase estimate based on a selection criteria; and combining the count and the selected fractional phase estimate to compute the distance. The fractional phase estimates can include a first fractional phase estimate having a lower resolution and higher accuracy in the presence of frequency errors relative to a second fractional phase estimate and wherein the second fractional phase estimate has more resolution and lower accuracy in the presence of the frequency errors relative to the first fractional phase estimate.

Abstract: Injecting pad bits during a read operation to improve format efficiency is disclosed. In some embodiments, a pad sequence associated with error correction is not stored in a sector on a disk. Instead, the pad sequence is merged at a read channel with data stored in a sector that is accessed by the read channel.

Abstract: A wireless inductive coupling assembly for a heated glass panel assembly is provided that includes a metal oxide coated glass panel with a panel frame, an opening frame that cooperates with the coated glass panel frame to allow the panel to cover a panel opening, a receiving coil that is positioned in the panel frame and that is wired to the panel, and a sending coil that is positioned in the opening frame and that is wired to an electrical power source. When the electrical power source supplies electrical power to the sending coil, the sending coil wirelessly induces an electrical current in the receiving coil, which causes the dielectric panel to provide heat.

Abstract: A method for writing data in a tape drive is provided by the present invention. The present invention provides a method for writing data in a tape drive. The invention include allocating a blank area for transpose writing on a magnetic tap and then writing a first group of data sets on the magnetic tape adjacent to the blank area. The tape drive maintains full operating speed during intervals between writing successive data sets, resulting in spaces between the data sets. At a specified interval, the drive repositions the tape writes a transposed data block to the allocated blank area, wherein the transposed data block contains the same content as the first group of data sets. A new blank area for transpose writing is then allocated adjacent to the recently transposed data block.

Abstract: A wireless inductive coupling assembly for a heated glass panel assembly is provided that includes a metal oxide coated glass panel with a panel frame, an opening frame that cooperates with the coated glass panel frame to allow the panel to cover a panel opening, a receiving coil that is positioned in the panel frame and that is wired to the panel, and a sending coil that is positioned in the opening frame and that is wired to an electrical power source. When the electrical power source supplies electrical power to the sending coil, the sending coil wirelessly induces an electrical current in the receiving coil, which causes the dielectric panel to provide heat.

Abstract: Copyright of contents to be transmitted may be protected for an analog signal produced by converting a digital signal representative of the contents. A signal transmission apparatus determines whether the contents are protected by copyright by detecting copyright protection information of a digital image signal of the contents at a protection information detecting unit, and scrambles an analog image signal converted from the digital image signal to output when the copyright is protected, or prohibits outputting of the analog image signal. When a receiving apparatus receives a transmitted signal, the apparatus generates a digital image signal and the analog image signal based on the transmitted signal.

Abstract: The present invention provides servo band recorded magnetic tapes, manufacturing method of the tapes, servo band writers and servo band Writing method. The background magnetic flux transition zone is generated with one directional polarization of the magnetization along the servo bands on the magnetic recording tapes. The servo stripes are generated with the reverse polarity of magnetization in the background magnetic flux transition zone. Then the magnetic flux servo transition against the background has more contrast so that the detected servo signal which is differential signal can be maintained in a high level.

Abstract: A storage device in which file data is divided into multiple blocks for storage on a recording medium. The storage device includes an additional data storing section for storing additional data to be recorded on the recording medium in association with the data to be written, a position determining section for determining recording positions on the recording medium where the blocks should be respectively written, based on the additional data, and a block writing section for writing the respective blocks on the recording positions on the recording medium determined by the recording position determining section. The additional data thus defines a gap length between blocks of recorded data. During a read operation, if the gap length does not comport with the additional data, then an error is assumed.

Abstract: Techniques are provided for detecting and correcting polarity reversals in signals generated by read/write heads that are used to read magnetic data. Directional patterns are stored in regions of each data track. The directional patterns are used to indicate whether the read/write head has reversed polarity. The read sensor reads the directional patterns along with other data stored on the disk. Electronic circuitry decodes the directional patterns to determine if the read/write head has reversed polarity. If the circuitry determines that the polarity of the read/write head has reversed, the circuitry reverses the polarity of output signals generated by the read sensor to correct for the polarity reversal of the head.

Abstract: In recovering data originally written on a carrier of magnetic media after a catastrophic failure, data may be read without prior knowledge of the write channel by which the data was originally written and in the presence of intersymbol interference of the readback signal. This is accomplished by forming an image of the spatial response function of the magnetoresistive transducer used to recover the data and by forming an image of the raw data read from the carrier of magnetic media by the magnetoresistive transducer for which the response function has been characterized. An image of the distribution of virtual magnetic charge on the carrier of magnetic media is obtained through deconvolution of the image of the response function of the magnetoresistive transducer and the raw readback signal. The readback signal corresponding to the data originally written on the carrier of magnetic media is then recovered by spatial differentiation of the image of virtual magnetic charge.

Abstract: A method and system for rewriting data on a tape when an error occurs during an initial write operation. When the initial write error occurs, the data is rewritten at a location that is a pre-defined block gap distance from the last valid write location on the tape. By measuring the length of the pre-defined block gap distance, the cause or causes of the write error or errors are known. Thus, the pre-defined block gap not only ensures that the data is not re-written in a no-write zone of the tape, due to the zone known to be error prone, but a historical record of past write errors is logged based on the length of the block gaps.

Abstract: A data storage device includes a track layout having three data sections. A first spin pad having a first length is located between a first and second data section. A second spin pad having a length that is different from the first length is located between the second data section and a third data section. A method for determining the lengths of the spin pads is also provided.

Abstract: A patterned media having recordable and non-recordable regions is initialized by first erasing (e.g. DC magnetizing) at least a portion of the recordable regions. At least one offset may then be determined. The at least one offset may compensate for a read to write delay in the electronics and/or at least one delay caused by the space separation between a read and a write head. A plurality of position error signal (PES) bursts may then be written on at least a portion of the recordable regions. During the write process, the previously written PES bursts are read and used to determine PES signals (e.g. servo signals) in order to guide the write head while writing new PES bursts. Magnetically written gray code may then be written on the media. The magnetically written gray code may be used to define a track number for the data tracks with no eccentricity.

Abstract: Accordingly, an improved method for recording data on an optical medium is disclosed which includes receiving and encoding a first set of data frames by a CIRC encoder to generate a second set of data frames. A control byte is then added to each of the second set of data frames to generate a third set of data frames. The third plurality of frames of data are received and encoded at an EFM encoder to generate a section comprising a plurality of Channel frames. The control byte of a sequentially first one of the third set of data frames is replaced with a SYNC 0′ byte selected from the limited group of previously unassigned fourteen-bit combinations. The control byte of a sequentially second one of the third set of data frames is also replaced with a SYNC 1′ byte selected from the same group.

Abstract: A sequence of data blocks written onto a medium of a data storage system includes first and subsequent appended data blocks having an append point code for identifying the first appended data block location. For data blocks having a running block number or frame number, the block or frame number of the first appended data block is stored as the append point code. The appended point code identifies the most recently append point location and aids in processes, such as tracking calibration, data integrity confirmation and track positioning.

Abstract: A method and system for determining data sector splits across servo bursts in a disc drive having a data disc with an embedded servo configuration. The disc drive includes a data transducer selectively positionable over the data disc for transferring data to and from the data disc, and the data disc includes a plurality of zones of predefined tracks. The method includes locating one or more frame table parameters based on a new zone position, creating a plurality of new frame table entries, while the disc drive is in operation, based on the frame table parameters, and moving the data transducer from a past zone position to the new zone position. The disc drive includes parameter memory and frame table memory. The parameter memory contains a plurality of zone records, with the zone records containing a plurality of zone table parameters. The frame table memory is utilized to store a frame table.

Abstract: An apparatus and method for writing data to a magnetizable recording medium in the form of spaced-apart magnetic flux transitions forming magnetization vectors having alternating magnetic orientations and selected lengths. A write element adjacent the medium includes a leading edge and a trailing edge forming a write gap which, when the write element is activated by an electric current, provides a write field for selectively magnetizing the magnetizable medium. A write driver circuit is responsive to a data input stream in providing a write current activating the write element, the write current comprising a pulse current in a phased relationship with a continuous current.

Abstract: A method and system of identifying and compensating for the cumulative effect of once per revolution, OPR, timing errors by modulating the size of an inter-sector runout (ISR) field between servo sectors. The ISR field is part of an inter-sector gap (ISG) field. The method begins when the nominal data field frequency is increased by one-half of the spin speed tolerance to guarantee adequate data field tolerances at the fastest portion of the timing OPR error curve. The ISR field is added to the disc format and maintained as a rotationally varying field. The ISR field is varied rotationally from a minimum of zero to a maximum equal to the timing OPR error tolerance. The size of the ISR field is varied rotationally based upon a calibration table that is used to identify the location of the disc drive head and to compensate for the appropriate timing OPR error at that location. The remainder of the ISG field is used to compensate for fixed timing errors.

Abstract: Reducing the gap distance between existing data and appended blocks increases the information density written onto magnetic tape. A narrow gap spacing may be achieved by reading the existing block of data with a read module leading the write module in the tape direction. The end of the existing data is determined from data read by the leading read module. Delaying appending data by a gap period introduces the gap between the existing block of data and the new block of data to be appended. The new block of data is written following the gap and verified by reading with a read module following the write module in the tape direction.

Abstract: The actual data recording area on a recording medium is expanded by reducing a gap area between blocks of data for compensating for a delay time of data conversion while recording and reproducing data in a data recording and reproducing device. Based on a servo sector signal, a data sector generator circuit generates a write data sector signal indicating a timing of data recording in a data recording area, and outputs the write data sector signal to a delay circuit and a selector having two input ports and one output port. The delay circuit generates a read data sector signal by delaying the write data sector signal by a certain period, and outputs the read data sector signal to the selector. The selector outputs the write data sector signal when a write mode signal is active, and outputs the read data sector signal when the write mode signal is inactive.

Abstract: In a data storage system in which a sequence of data blocks is written onto a medium, appended data is distinguished by including in the first and subsequent appended data blocks an append point code uniquely identifying the location of the first appended data block. Where the data blocks have a running block number or frame number, the block or frame number of the first appended data block is stored as the append point code. This clearly identifies the most recent append point location which will aid in processes such as tracking calibration data integrity confirmation and track positioning.

Abstract: The present invention provides methods and apparatus for locating target positions within an encoded data stream, where the encoded data stream incorporates special, reserved codewords to represent host data structure information, such as file marks and record boundaries. The encoded data stream can also only be read or decoded in the forwards direction. Incorporation of the special codewords obviates an index associated with the encoded data to support navigation within the encoded data stream. The methods and apparatus locate target positions by decoding the data until the target position is encountered, and provide mechanisms to enable location of target positions that are specified as being backwards, relative to a current position in the encoded data stream.

Abstract: A method of reproducing digital signals recorded on a disk having first and second recording surfaces. The digital signals are in the form of a data frame including a lead-in block and n data blocks. The lead-in block has a same format as the n data blocks. n block addresses are assigned to the n data blocks. Information identifying an area on the disk in which the n data blocks is recorded is assigned to the n data blocks. m data blocks (0<m<n) are recorded on the first recording surface, and remaining (n−m) data blocks are recorded on the second recording surface. The lead-in block is recorded at the head of the data frame, and includes recording area identifying information identifying an area on the disk in which the lead-in block is recorded, and disk information identifying (1) a number of recording surfaces, (2) the block address of one of the m data blocks recorded last on the first recording surface, and (3) the block address of a last one of the n data blocks in the data frame.

Abstract: An actuator is provided with a step so as to allow FPC mounting surfaces of a read/write FPC band and of a relay FPC to be level with each other. Pointer information P4 in a ROM table is used to refer to a RAM table to acquire offset correction data. On-track control is effected at a cross point of two-phase servo signals N and Q. A value of this cross point is measured to find a position sensitivity correction value. A gap corresponding to encode loss is provided at the trailing position of each of sectors. In read operation, a sector pulse is generated with a delay corresponding to decode loss.

Abstract: The system for gap positioning optimization in a tape drive takes advantage of the presence of a pair of read heads, located one on either side of the write head, to precisely determine the boundary between the inter-block gap and the data blocks adjoining the inter-block gap. In particular, the servo mechanisms in the tape drive note the location of the boundary between the present data block and the inter-block gap formed a the end of the present data block. When the tape is repositioned between data read/write operations, this servo information is used to identify this boundary to initiate the subsequently received data read/write operation. A predetermined amount of inter-block gap is provided at the end of the data block to ensure that subsequently received data is not written on top of the present data block or the overwriting of the next data record begins at the beginning of the data block.

Abstract: An apparatus for recording and reproducing a signal using a thin film magnetic tape as a medium and using ring type magnetic heads for recording and reproducing the signal, wherein the gap length of the magnetic head for reproducing is larger than the gap length of the magnetic head for recording. Maximum recording and reproducing performance is achieved by implementing separate recording and reproducing heads.

Abstract: An apparatus and formatting method formats a disk without using an index pulse generated by hardware for every disk rotation. A last data block gap and a track gap which are longer than a standard track gap length are first written. Even if there is a fluctuation in rotation cycle time during formatting, a last sector of each track is written over a beginning of the track gap. When writing to a last sector is complete, formatting of a track is complete. When a head is stably positioned at a track to be formatted, formatting of the track is started.

Abstract: A method of and a system for efficiently using split information stored in an unnecessary data sector, thereby reducing unnecessary data.

Abstract: A reproducing apparatus for disk-shaped recording medium rotationally drives the disk-shaped recording medium at a particular speed to read information from a recording track disposed circumferentially to the center of the recording surface with information recorded at a constant linear velocity. A pickup means scans the recording track and generating a first reproduction signal. A first rotational drive control means rotates the disk-shaped recording medium at a constant linear velocity based on the reproduction signal, and a second rotational drive control means rotates the disk-shaped recording medium at a constant angular velocity. A rotational drive control means selection means selects the first rotational drive control means or the second rotational drive control means based on the position of the pickup means when reproducing the disk.

Abstract: A method and arrangement for storing on tape information produced by a switching exchange system, by reading data into an intermediate file for increasing the number of records to be stored to an amount suitable for the capacity of the recorder used; copying the intermediate file into a backup storage; and emptying the intermediate file to a tape for a new read cycle of information produced by the switching exchange system.

Abstract: There is described a tape format and a method for formatting a length of magnetic tape with a number of system zones. Each system zone contains an area for mechanical load/unload operations or threading operations and an area containing volume format information for the entire magnetic media.

Abstract: Disclosed is a PRML regenerating apparatus for regenerating a signal read by a head from a storage medium. This PRML regenerating apparatus has a waveform equalizing circuit for waveform-equalizing the read signal, a maximum-likelihood decoder for maximum-likelihood-decoding, after obtaining a determination value by comparing the equalized output with upper and lower slice levels, this determination value and a control circuit for setting variable a distance between the upper slice level and the lower slice level of the maximum-likelihood decoder. The distance between the upper and lower slice levels can be thereby set variable in accordance with an equalization characteristic. A ternary determination circuit of the maximum-likelihood decoder is constructed of a memory for storing a correspondence table of the equalized output and the upper or lower slice level versus the determination result and the next upper or lower slice level.

Abstract: To increase the recording capacity of a magnetic disc, tracks of this magnetic disc are divided into a number of sectors, with each sector being formed from a number of segments. Each segment is basically made up of a data region and a servo region with data being recorded on the data region and a clock pattern which becomes the basis for generation of a clock, a fine pattern which becomes the basis for the tracking operation, and an access pattern which becomes the basis for a seek operation being recorded on the servo region. An ID region and servo region are formed before the data region and servo region which make up the leading segment with the sector ID for this region being recorded in this ID region. After this ID has been read from this ID region, while it is being determined whether or not this ID is the same as the designated ID, the servo operation corresponding to the servo control signal occurring in the servo region is carried out.

Abstract: An apparatus and a method for operating a disk drive are described where defect information is written in a field other than an identification (ID) or header field in a data sector. Rather, defect information is written to a field, preferably an unused field like a sector gap or write-to-read gap. By placing defect information in the sector gap, or the like, disk capacity for user data is improved. Also, as in headerless and merged identification data formats, defect information does not need to be stored in an off-disk memory such as a random access memory (RAM).

Abstract: A servomechanism for controlling the position of a magnetic-tape playback head (16) with respect to a track (24) of digital data on a magnetic tape (22) positions the head by reference to an error signal that error-signal-generation circuitry (FIG. 10). generates. Sample-clock signals obtained from simultaneously read azimuth-recorded data tracks clock respective frequency dividers (52 and 54), and a phase detector 56 generates the error signal by comparing the frequency dividers' outputs.