Methods and apparatus for overlapping data tracks on a storage medium

A narrow read head and a wider write head are used to store and retrieve data from a storage medium, such as a magnetic disk or tape. The wider write head is selectively positioned to record overlapping data tracks. The read head is subsequently positioned to read the non-overlapping portions of the data tracks. In one format, a read seldom data block is recorded by sequentially recording a plurality of data tracks such that each subsequent data track partially overlaps a previously written data track. In another format, pairs of data tracks are recorded by side-by-side, wherein within each pair of data tracks there is an overlapping region. In either format, the narrower read head is positioned to read the non-overlapping portions of the data tracks. Consequently, the storage capacity of the storage medium is optimized to take advantage of the narrow read head.

FIELD OF THE INVENTION
 The present invention relates to data storage devices, and more
 particularly to methods and apparatus that provide for more efficient use
 of the recording space available on a storage medium and an increase in
 the data storage capability of a storage device.
 BACKGROUND OF THE INVENTION
 Data storage devices are commonly used in computer systems to store large
 amounts of data. Certain types of data storage devices, such as tape
 drives, are normally used to provide archival storage of large amounts of
 data. Other types of data storage devices, such as disk drives, are
 typically used in workstations, personal computers, laptops and mainframe
 computer systems to store large amounts of data that can be quickly stored
 and retrieved.
 Each of these exemplary data storage devices, i.e., the tape drive and disk
 drive, utilizes a data storage medium on which information is stored in
 the form of data. The storage medium in a tape drive is typically a
 magnetic tape, and the storage device in a disk drive is typically a
 magnetic disk, although other types of drives use other types of disks
 (e.g., optical disks). A tape drive normally comprises a servoing system
 configured to move the tape past one or more transducers arranged to
 read/write data on the tape. A disk drive generally comprises at least one
 magnetic disk that is rotated about an axis by a spindle motor and
 positioned to be accessed by one or more transducers. The surfaces of both
 the tape and the disk are typically divided into a series of data tracks.
 The data tracks on a tape can take several different shapes, including,
 for example, helical, arcuate and linear shapes. The data tracks on a disk
 usually extend circumferentially, typically in a concentric pattern,
 around the disk. Each data track, on either a magnetic tape or magnetic
 disk, stores data in the form of magnetic transitions on a recordable
 surface of the tape/disk. For example, each transition can represent a bit
 of information.
 It is expected that users of disk drives and tape drives will place ever
 greater demands on manufacturers with regard to the amount of data that
 can be stored on and retrieved from a data storage device. This is
 especially true for modern software programs, which include graphics and
 other data structures that dramatically increase the amount of data that
 needs to be accessed. In addition, the rapid growth and the use of servers
 on computer networks requires large storage capabilities to accommodate
 the data needs of a larger number of users on the network who utilize
 network based servers and/or shared resources.
 In recent years, the trend has been to design and build data storage
 devices that are capable of supporting these increasing needs. For
 example, one trend has been to provide disks that can support more
 information (often in a more compact size), and that can be operated at
 higher rotational velocities to increase data read and write rates. One
 consequence, however, of these improvements is that the data density on
 the recordable surface of the disks/tapes and the associated speeds of the
 disks/tapes are approaching the perceivable limits of conventional
 transducers and associated circuitry to rapidly and accurately read/write
 the closely spaced, fast-moving magnetic transitions required by such
 storage devices.
 By way of example, in order to meet the data reading requirements in a
 conventional disk drive, a magnetoresistive (MR) transducer is typically
 used. The MR transducer is coupled to an electronic read channel that
 implements signal processing techniques, such as partial response maximum
 likelihood (PRML) detection. The MR transducer is configured to sense the
 magnetic transitions on the disk drive, and to produce a corresponding
 change in electrical resistance as a function of a change in magnetic flux
 on the disk. The MR transducer is coupled to an electronic circuit, for
 example, a pre-amplifier that detects the resistance changes in the MR
 transducer and generates one or more corresponding electrical signals that
 vary in time as a function of the resistance. Thus, the typical
 pre-amplifier outputs a signal that corresponds to the data recorded as
 magnetic transitions on the disk surface. This signal is then supplied to
 the remaining portions of the read channel which essentially
 extract/interpret the data represented within the signal.
 A write channel is basically the opposite of the read channel, in that an
 electrical signal representing data is provided to a write head which is
 configured to affect the magnetic flux on the recordable surface and
 record the data as transitions therein.
 However, because of differences in fabrication and manufacturing processes,
 a typical write head is much larger (e.g., twice as large or larger) than
 a read head equipped with an MR transducer. By way of example, it is
 possible given current technology to manufacture a read head that is
 narrow enough to read 25,000 tracks per inch (TPI). Write heads narrow
 enough to write 25,000 TPI are not known to date.
 Thus, there is a need for methods and apparatus that effectively take
 advantage of the higher TPI capability of a narrow read head while also
 using a significantly wider write head.
 SUMMARY OF THE INVENTION
 The present invention provides methods and apparatus that allow overlapping
 data tracks to be stored on a recordable surface of a storage medium. The
 methods and apparatus provide differing data track storage formats, each
 of which advantageously increases the track pitch to take advantage of a
 read transducer that is narrower than a corresponding write transducer.
 This is accomplished by selectively overlapping wide data tracks during a
 write operation, while leaving enough of each data track to be
 subsequently read by the narrower read transducer during a read operation.
 In accordance with one aspect of the present invention, a "wide-write and
 narrow-read" method is provided for use in a disk drive having a write
 head and a narrower read head. The method includes writing a plurality of
 data tracks on an information storage disk with a write head, such that a
 subsequently written data track partially overlaps a previously written
 data track. The method then includes reading a non-overlapped portion of
 at least one of the plurality of data tracks with a read head.
 In accordance with another aspect of the present invention, a method is
 provided for writing a plurality of tracks of data on, and reading the
 plurality of tracks of data from, a storage medium. The method includes
 writing a first track of data along a first path, the first track of data
 having an initial width, and writing a second track of data along a second
 path, the second track of data having the same initial width, as the first
 track of data. The second path substantially follows the same direction as
 the first path, however a portion of the second track overlaps a portion
 the first track of data. Consequently, there is provided a reduced first
 track of data having a reduced width that is narrower than the initial
 width. The method subsequently includes reading at least a portion of the
 reduced first track of data and at least a portion of the second track of
 data with a read transducer. In certain embodiments this method further
 includes writing a third track of data along a third path and a fourth
 track of data along a fourth path such that the third and fourth paths
 substantially follow the same direction of the second path, and a portion
 of the fourth track of data overwrites a portion the third track of data.
 As a result, a third track of data that has a reduced width is provided.
 However, even after writing the third track of data the second track of
 data still has an initial width. In certain embodiments, the storage
 medium is an information storage disk, while in other embodiments, the
 storage medium is an information storage tape.
 The above stated needs are also met by an apparatus, in accordance with one
 aspect of the present invention, for use in a data storage device in
 writing data to a storage medium via a write transducer, and reading the
 data from the storage medium via a read transducer. The apparatus includes
 logic which is configured to respond to at least one control signal
 associated with an accessing operation by outputting a signal to an
 actuator that is arranged to position the write and read transducers with
 respect to the storage medium. For example, the signal for a write
 accessing operation causes the write transducer to write at least one
 subsequent data track over at least a portion of a previously written data
 track, and the signal for a read accessing operation causes the read
 transducer to read at least a portion of a remaining portion of a
 previously written data track.
 The foregoing and other features, aspects and advantages of the present
 invention will become more apparent from the following detailed
 description of the present invention when taken in conjunction with the
 accompanying drawings.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
 The methods and apparatus of the present invention take advantage of the
 current state of technology in which it is possible to manufacture a read
 head that is significantly narrower than with a corresponding write head.
 The methods and apparatus of the present invention are readily adaptable
 for use in otherwise conventional data storage devices. The methods and
 apparatus of the present invention are directed towards increasing the
 density of the data stored on a storage medium by selectively overlapping
 data tracks written by the wider write head such that the narrower read
 head can then read the portions of the data tracks that have not been
 overlapped by another data track.
 While the methods and apparatus of the present invention are described,
 hereinafter, in accordance with certain exemplary embodiments that are
 directed towards a disk drive, it is intended that the same methods and
 apparatus are readily applicable to other types of data storage devices,
 such as, for example, tape drives, that have read and write heads of
 differing sizes.
 FIG. 1 is a block diagram of a conventional computer system 2 having a
 processor 4, a network or bus 6, a primary memory 8, and one or more
 secondary memory devices 10. Processor 4 is configured to implement
 computer instructions and process data, as is well known. The processor 4
 accesses primary memory 8 and secondary memory devices 10 over bus 6.
 Primary memory 8 is typically a random access memory (RAM). Secondary
 memory devices 10 can include a tape drive, a hard disk drive, a floppy
 disk drive, an optical drive, and/or other like secondary memory storage
 devices. Those skilled in the art will recognize that other computer
 system configurations, for example, having additional buses, interfaces
 and peripheral devices, are also common.
 FIG. 2 is a block diagram depicting an exemplary conventional secondary
 memory device 10, such as a tape or disk drive data storage device.
 Secondary memory device 10 includes an interface unit 11 for interfacing
 with bus 6, a control logic unit 12, a storage medium transport unit 14, a
 read/write transducer unit 16, and a storage medium 18. Control logic unit
 12 is coupled to interface unit 11 and is configured to control the read
 and write operations conducted within secondary memory device 10 in
 response to one or more control signals received over bus 6. For example,
 processor 4 may assert a seek control signal over bus 6 that is received
 by interface unit 11. In one example, the seek control signal causes
 control logic unit 12 to seek and/or scan over a particular data track on
 storage medium 18 for use in a read and/or write operation.
 Control logic unit 12 is coupled to storage medium transport unit 14 and
 configured to cause storage medium transport unit 14 to move or otherwise
 position storage medium 18 in a particular manner. For example, in a tape
 drive unit, storage medium transport unit 14 is responsible for moving the
 storage medium 18, in this case a magnetic tape, in accordance with
 control signals from control logic unit 12. In a disk drive unit, for
 example, storage medium transport unit 14 can include a motor controller
 circuit coupled to control a spindle motor that is configured to spin the
 storage medium 18, in this case one or more disks.
 Control logic unit 12 is further coupled to read/write transducer unit 16
 and configured to control the timing and positioning of one or more
 read/write transducers via the circuitry and mechanisms provided in
 read/write transducer unit 16. Read/write transducer unit 16 is arranged
 to read and write data from storage medium 18 in accordance with control
 signals received from control logic unit 12.
 FIG. 3 depicts an exemplary conventional disk drive 20 that is adaptable
 for use with the present invention. Disk drive 20 includes a plurality of
 storage disks 22a-d and a plurality of read/write heads 24a-h. Each of the
 storage disks 22a-d is capable of storing a plurality of data tracks. As
 illustrated in FIG. 3, a read/write head 24a-h is provided for each
 surface of each of the disks 22a-d such that data can be read from or
 written to the data tracks on storage disks 22a-d.
 It should be understood that disk drive 20 is merely representative of a
 disk drive system that can be used in the present invention and that the
 present invention can also be implemented on a disk drive system including
 more or less storage disks, and/or additional elements.
 Referring to FIG. 3, storage disks 22a-d are mounted for rotation by a
 spindle motor arrangement 29, as is known in the art. Additionally,
 read/write heads 24a-h are supported by respective actuator arms 28a-h for
 controlled positioning over pre-selected radii of the storage disks 22a-d
 to enable the reading/writing of data on the data tracks. Actuator arms
 28a-h are rotatably mounted on a pin 30 and controlled by a voice coil
 motor 32 that is operable to controllably rotate actuator arms 28a-h
 radially across storage disks 22a-d.
 Each of the read/write heads 24a-h is mounted to a respective actuator arm
 28a-h and comprises a magnetic transducer structure 25 mounted to a slider
 26. For high performance operation, magnetic transducer structure 25
 typically includes a pair of transducers, including a narrow
 (magnetoresistive) MR transducer that serves as a read head, and a wider
 inductor that serves as a write head. In most conventional disk drive
 systems, sliders 26 cause magnetic transducer structures 25 of read/write
 heads 24a-h to "fly" above the surfaces of the respective storage disks
 22a-d for non-contact operation of the disk drive system. When not in use,
 voice coil motor 32 rotates actuator arms 28a-h to position read/write
 heads 24a-h over a respective landing zone 60 (see FIGS. 4 and 5).
 A printed circuit board (PCB) 34 is provided to mount control electronics
 for controlled operation of spindle motor 29 and voice coil motor 32. The
 PCB 34 also includes read/write channel electronics circuitry, which is
 coupled to the read/write heads 24a-h to control the transfer of data to
 and from the data tracks on storage disks 22a-d.
 FIG. 4 is a block diagram illustrated in schematic form of an exemplary PCB
 34 and the electrical couplings between the control electronics on PCB 34
 and the components on the disk drive system described above. A
 microprocessor 35 is coupled to a read/write controller 36, a spindle
 motor controller 38, an actuator controller 40, ROM 32, and RAM 43.
 Microprocessor 35 sends data to, and receives data from, the storage disks
 22a-d via read/write controller 36 and read/write heads 24a-h.
 Microprocessor 35 also operates according to instructions stored, for
 example, in ROM 42 to generate and transmit control signals to motor
 controller 38 and actuator controller 40. Motor controller 38 is
 responsive to the control signals received from microprocessor 35 to
 generate a drive voltage to spindle motor 29 (FIG. 3) to cause storage
 disks 22a-d to rotate.
 Similarly, actuator control 40 is responsive to the control signals
 received from microprocessor 35 to generate a voltage to voice coil motor
 32 to controllably rotate read/write heads 24a-h, via actuator arms 28a-h,
 to pre-selected radial positions over storage disks 22a-d. The magnitude
 and polarity of the voltage generated by actuator control 40, as a
 function of the microprocessor control signals, typically determines the
 radial direction and speed of read/write heads 24a-h.
 Microprocessor 35 is configured to determine the current radial position of
 read/write heads 24a-h, and the radial position of the data track to where
 read/write heads 24a-h are to be moved. Once the new position is
 determined, microprocessor 35 implements a seek operation wherein the
 control signal generated by microprocessor 35 for actuator controller 40
 causes voice coil motor 32 to move read/write heads 24a-h from the current
 data track to a destination data track at the desired radial position
 (e.g., sector).
 Read/write controller 36 further includes a read channel that, for example,
 implements signal processing techniques such as partial response, maximum
 likelihood (PRML) detection to process the electrical signals output by
 the MR transducer in read/write heads 24a-h, during a read operation.
 Similarly, read/write controller 36 includes a write channel that supplies
 electrical signals to the write head in read/write heads 24a-h, during a
 write operation. As is known in the art, RAM 43 is typically used to
 buffer the data that is read from, or to be written to, storage disks
 22a-d.
 FIG. 5 depicts an exemplary storage disk 22 for use in disk drive 20, for
 example, having at least one disk surface 23 that provides a recordable
 area upon which a plurality of data tracks 62 can be recorded. Associated
 with storage disk 22, there is an inside circumference 58 and an outside
 circumference (near landing zone 60). Between these points, as depicted in
 FIG. 5 with dashed lines, there is a recordable surface on which a
 plurality of data tracks 62 can be recorded and subsequently read.
 Storage disk 22 can further be formatted in a number of ways, such that the
 data stored within particular data tracks is recoverable by referring to
 positional coordinates associated with the formatting of the storage disk
 22. For example, storage disks 22a-d can be divided into a plurality of
 sectors and data tracks, as is well known. The positioning of read/write
 heads 24a-h above the recordable surface of storage disks 22a-d during a
 write operation and a subsequent read operation is dependent on the
 formatting of the plurality of data tracks 62.
 The methods and apparatus of the present invention are directed towards
 increasing the density of the plurality of data tracks 62, or a subset
 thereof. There are at least two different formats, each of which are
 novel, for the recording of data tracks 62 that are supported by the
 methods and apparatus of the present invention. A first format is a "write
 seldom" format that maximizes the density of data tracks 62. A second
 format is a "paired" format that increases the density of data tracks 62
 while also allowing for each of the data tracks to be written at any time.
 These formats are discussed in detail below, following a discussion of the
 controlling mechanisms that are used to align the read and write heads in
 accordance with one of these formats.
 FIG. 6 is a block diagram that depicts an improved actuator controller 40'
 that, in accordance with an exemplary embodiment of the present invention,
 responds to a plurality of control signals (e.g., from microprocessor 35),
 and supplies a modified microjog control voltage signal to voice coil
 motor 32. This modified microjog control voltage signal modifies the
 positioning of read/write heads 24a-h during read and write operations to
 enable the formatting of the plurality of data tracks 62 in accordance
 with the various embodiments of the present invention.
 Actuator controller 40' includes a servo circuit 70 that is coupled to
 receive conventional control signals from microprocessor 35. Servo circuit
 70 also receives positional feedback information from voice coil motor 32,
 and/or other feedback devices configured to provide positional information
 with regard to the positioning of actuator arms 28a-h.
 In accordance with an exemplary embodiment of the present invention,
 actuator controller 40' further includes a selector circuit 72 that is
 coupled to receive control signals from microprocessor 35. As shown, servo
 circuit 70 and selector circuit 72 each receives conventional track/sector
 signal(s) from microprocessor 35 during a read and/or a write operation.
 Selector circuit 72 is further configured to receive one or more control
 signals from microprocessor 35 that identify whether a read or write
 operation is occurring, and optionally if a "write seldom" block of data
 tracks is to be written. The write seldom format is discussed in detail
 below.
 Because selector circuit 72 adjusts the positioning of read/write heads
 24a-h in accordance with the formatting of the present invention, selector
 circuit 72 is configured to output an offset signal that is then added to
 the conventional microjog signal output by servo circuit 70. A
 conventional microjog signal is used to position the read/writes heads
 24a-h to a particular track, based on a previous position. In certain
 embodiments of the present invention, the offset signal from selector
 circuit 72 is supplied to an adder 74, along with the microjog signal from
 servo circuit 70. Adder 74 is configured to combine the microjog signal
 and offset signal to produce a modified microjog control signal that is
 then applied to voltage coil motor 32. Because of the added offset, the
 positioning of read/write heads 24a-h will have been modified in
 accordance with one of the data track formats of the present invention.
 FIGS. 7-10 depict exemplary data tracks that are recorded in accordance
 with the different formats of the present invention. Note that for ease of
 illustration, the data tracks depicted in FIGS. 7-10 are each depicted as
 being both straight and extraordinarily uniform. In an actual arrangement,
 the data tracks will typically not be this uniform and depending upon the
 type of storage medium and storage device configuration the data tracks
 will not necessarily be straight. For example, as depicted in FIGS. 3, 4,
 and 5, in a disk drive, the plurality of data tracks form concentric rings
 about a common axis.
 In FIG. 7, there is illustrated a plurality of data tracks 62, including
 data tracks 62a-e, which are recorded in a write seldom format. As shown,
 data tracks 62a-e are each partially overlapped by a subsequently recorded
 data track. In particular, data track 62a which has an initial width 80,
 as defined by the width of the write head 24w, has been partially
 overlapped by subsequently recorded data track 62b. Data track 62b also
 has initial width 80 because it was also written by write head 24w. Data
 track 62b has been partially overlapped by a portion of subsequently
 recorded data track 62c. Similarly, data track 62c is partially overlapped
 by subsequently recorded data track 62d. As shown, data track 62e is being
 recorded by write head 24w and is partially overlapping data track 62d.
 Each of the overlapped portions of data tracks 62a-e form an overlap
 region 82.
 Write head 24w, in accordance with an exemplary embodiment of the present
 invention, is positioned in response to the modified microjog voltage
 signal from actuator control 40' to write data tracks 62a-e along specific
 paths (e.g., as depicted by the arrow leading away from write head 24w) in
 order to overlap the data tracks.
 The plurality of data tracks 62 in FIG. 7 optimize the use of a write head
 24w having a writing width that is substantially equal to initial width
 80, and a read head 24r as depicted over data track 62b that has a narrow
 reading width that is less than the initial width 80.
 Thus, as shown in FIG. 7, with this exemplary write seldom format there is
 a reduced width 84 within each of the plurality of data tracks 62 that is
 not overlapped by subsequent data tracks. Reduced width 84, therefore,
 represents the portion of each of the plurality of data tracks 62 wherein
 read head 24r can read the data, successfully, for the associated data
 track. For example, as depicted in FIG. 7, read head 24r is positioned to
 read the data recorded within the reduced width 84 of data track 62b. By
 applying the proper offset signal to adder 74 according to the present
 invention, the width of the resulting data tracks approaches the reading
 width of read head 24r. Thus, the write seldom format in FIG. 7 allows for
 a maximum track density that is based on the reading width of read head
 24r.
 In storage mediums having concentric data tracks, the write seldom format
 does not provide for selective re-recording of a data track within the
 plurality of data tracks 62. For example, to re-record data track 62c, it
 is necessary to write data tracks 62c, 62d and 62e over again and in
 sequence to avoid corrupting the data recorded in data track 62d while
 attempting to write track 62c. Thus, the write seldom format is useful for
 recording three or more data tracks when the data tracks are not required
 to be written over, or otherwise rewritten, very often. Hence, the name
 "write seldom" has been applied to such a format.
 A write seldom formatted data block, such as that depicted in FIG. 7, may
 be advantageous for storing particular types of data. For example, an
 operating system or other application program having data that is mainly
 accessed only during read operations could be stored in this more compact
 write seldom format. Additionally, the write seldom format is also useful
 in the archival storage of data that does not require write access.
 In accordance with still other exemplary embodiments of the present
 invention, a paired format that is provided for a plurality of data tracks
 62' is depicted in FIG. 8. In a paired format, the data tracks 62' are
 recorded in one or more pairs, such as pairs 86a and 86b. The pairs 86a
 and 86b each have two data tracks that are partially overlapped. For
 example, data tracks 62a and 62b form pair 86a, and data tracks 62c and
 62d form data track pair 86b. To store a large block of data a plurality
 of pairs, such as pairs 86a and 86b are used.
 Unlike the write seldom format of FIG. 7, the paired format as depicted in
 FIG. 8 allows for individual data tracks, within each pair 86a and 86b, to
 be recorded or re-recorded at anytime without corrupting any of the other
 data tracks. Because there are no shared or overlapped regions between
 pairs 86a and 86b there is no need to rewrite or otherwise coordinate the
 writing of data to the data tracks in pairs 86a and 86b.
 This feature of the paired format is illustrated in FIG. 9 wherein, for
 example, having previously written data track 62a-e, a subsequent write
 operation requires that data track 62c be re-recorded with new data. The
 rewriting of this data is depicted by write head 24w and new data track
 62c'. As shown, a new data track 62c' is being recorded over data track
 62c with write head 24w. Data track 62c' partially overlaps data track 62d
 as illustrated by overlap region 82'. Thus, by using a paired format,
 individual data tracks can be recorded during subsequent write operations
 without corrupting the other data tracks.
 Within data track pair 86a, data track 62a is referred to as the "odd"
 track and data track 62b is referred to as the "even" track. The
 positioning of read head 24r to read either of data track 62a (odd) or
 data track 62b (even) is determined, for example, by selector circuit 72
 in FIG. 6 based on the track/sector control signals from microprocessor
 35. For example, in certain embodiments selector circuit 72 records or
 otherwise determines the proper offset signal for a particular data track
 based on the control signals from microprocessor 35. The proper offset
 signal is selected as a function of the format and of the odd or even
 reference for the data track within a data track pair.
 In FIG. 10, data track pair 86a is shown as having several tracking
 approaches or paths which are represented by directional arrows. These
 paths are determined by the modified microjog signal, which includes the
 offset signal for the selected format and data track. As shown in FIG. 10,
 data tracks 62a and 62b have been recorded by selectively positioning
 write head 24w on parallel paths such that data tracks 62a and 62b form an
 overlap region 82. During a subsequent read operation, read head 24r is
 properly positioned to read each of the data tracks 62a and 62b by
 applying an offset signal that causes read head 24r to scan over the
 targeted data track without passing over overlap region 82. Thus, for
 example, if the formatting is write seldom (as in FIG. 7) then read head
 24r is positioned, via an offset signal, to read the data recorded within
 the reduced width 84 of data tracks. In a paired format, read head 24r is
 positioned, via an offset signal, to read the data recorded within the
 reduced width 84' of the targeted odd or even data track. For example, in
 pair 86a of FIG. 10 data track 62a is an odd track and data track 62b is
 an even track. Thus, in order to read the data recorded in data track 62a,
 the offset signal accounts for an odd track offset 90 to properly position
 read head 24r to read the data recorded in odd track 62a. In order to
 properly read an even data track, such as data track 62b, the offset
 signal accounts for an even offset 92 to properly position read head 24r
 over the reduced width 84' (see FIG. 8) of data track 62b. As such, in
 relationship to the alignment of write head 24w for each track, offsets 90
 and 92 cause read head 24r to be repositioned in opposite directions. For
 example, in certain embodiments, odd offset 90 is essentially a negative
 offset value and even offset 92 is a positive offset value. Odd track
 offset 90 also provides the proper offset for use in a write seldom format
 because read head 24r is thereby properly aligned to read the data from
 the reduced width area 84 (see FIG. 7) of the track being scanned.
 With the methods and apparatus of the present invention as described
 herein, it is possible to take advantage of the narrower read head
 technologies. By applying an offset signal for a particular format, the
 resulting track pitch is significantly increased over a standard
 implementation in which the track pitch is limited by the writing width of
 write head 24w. In the methods and apparatus of the present invention the
 track pitch is limited by the smallest of the heads which, in most cases,
 equates to the reading width of read head 24r. For example, if read head
 24r is one-half the size of write head 24w then a 33% increase in the
 track pitch is provided in the paired format of FIG. 8, and a 100%
 increase in the track pitch is provided in the write seldom format of FIG.
 7.
 Although the present invention has been described and illustrated in
 detail, it is to the be clearly understood that the same is by way of
 illustration example only and is not be taken by way of limitation, the
 spirit and scope of the present invention being limited only by the terms
 of the appended claims.