WO2001045092A2

WO2001045092A2 - Data storage system using synchronization signals incorporating servo information

Info

Publication number: WO2001045092A2
Application number: PCT/US2000/042748
Authority: WO
Inventors: R. Stockton Gaines; Alvin M. Despain
Original assignee: Acorn Technologies, Inc.
Priority date: 1999-12-14
Filing date: 2000-12-12
Publication date: 2001-06-21
Also published as: WO2001045092A3; WO2001045092A9

Abstract

Position control for a read head with respect to a track on a storage disk is improved using a synchronization pattern that includes servo information as well as synchronization signals used to set a clock for recovering data from a disk. A disk stores data along substantially concentric tracks positioned at varying radii on the disk's data storage surface, with the data organized into data blocks. Synchronization patterns are provided at the start of each data block from which a read head can derive a synchronization signal useful for reading data from the data block. This synchronization signal is input to a phase locked oscillator to train a phase locked detector that recovers data signals stored in the data block. Servo information, suitable for identifying a misalignment between the read head and the track being read is also provided within the synchronization pattern. This may be accomplished by providing a conventional synchronization pattern modulated with a two dimensional servo pattern that includes information about the relative position of the read head with respect to a track. Conventional sector or wedge servo information for positioning the read head with respect to a track may be provided in addition to the servo data provided for each data storage block.

Description

DATA STORAGE SYSTEM USING SYNCHRONIZATION SIGNALS INCORPORATING SERVO INFORMATION

BACKGROUND OF THE INVENTION

1 Field of the Invention

The present invention relates to data storage systems that incorporate withm a data structure synchronization signals facilitating the writing and reading of data and incorporate within the data structure servo signals for positioning a head with respect to the data structure More particularly, the present invention relates to high density storage disk drives that use synchronization patterns at the start of data blocks to synchronize data detection and that use servo information to position a head with respect to a track in a read or wπte operation

2 Description of the Related Art

Magnetic disk drive data storage systems provide high volume, long term data storage that is comparatively fast and relatively mexpensiv e, at least as measured on a per-bit basis For example, magnetic disk storage is faster than present optical storage options and is comparatively less expensive than present flash memory based storage devices Industry today relies on magnetic disk drives for long term data storage in vaπous types of computer systems and in certain consumer electronics applications such as video recording and playback, and both types of uses continue to grow Research into magnetic storage disk systems continues and the performance of such systems is expected to continue to improve Rotational storage devices and in particular disk drives store data on one or more faces of a rotating media, often referred to as platters or disks In the case of a conventional hard disk dπve, data are stored by generating a magnetic modulation withm a magnetic mateπal coated on a data storage surface of the disk. Data are read back by subsequently detecting this modulation with a read head Typically data are wπtten to a disk using a wπte element and data are read from the disk using a read element, where both the wπte and read elements are provided as physically distinct elements on a single head. By recording data m the form of magnetic signals on the rotating disk, data can both be stored and subsequently recovered after even long peπods of time Data may be organized into a plurality of radially displaced, tangentially extending tracks, with the data stored on the tracks generally organized into a plurality of data blocks To read or wπte data from or to a particular data block, the typical disk dπve positions the read and wπte head over the track containing the target data block location in what is known as a seek operation The read and wπte head of the disk dπve then reads or wπtes the data on the storage surface, as desired Data read and wπte operations, seek operations and other operations such as using codes such as Grey codes to identify track positions are descπbed m TJ S Patent No 5,523,902, U S Patent No 5,796,543, and U S Patent No 5,847,894, each of which is hereby incorporated by reference

FIG 1 illustrates schematically certain aspects of a storage surface 10 and of a disk dπve Generally, the disk 8 includes a central opening 12 through which passes the spindle of the disk drive and by which the disk and its storage surface are rotated An area 14 is provided on the disk around the central opening 12 for clamping or otherwise holding the disk to the spmdle, this area 14 is essentially unusable for storage The storage surface 10 extends radially away from the clamping area 14 and may terminate in a peπpheral band of the disk, not shown, that is also preferably not used for data storage In general, the storage surfaces of disk dπves may be considered substantially uniform or the storage surface might be divided into plural zones When the storage surface 10 is treated as substantially uniform, relatively little is done m the disk dπve to account for the differences between radially displaced data storage locations such as diffeπng rotational velocities and the associated differences in the areal density of stored data on the disk surface Another strategy subdivides the storage surface 10 into a number of radially extending bands, known as zones, such as the zones 16, 18 and 20 indicated on the storage surface 10 The vaπous storage locations withm the different zones 16, 18 and 20 are treated similarly, while the storage locations in different zones may be treated differently, for example by using different clock rates for reading or wπting different signals or by using different densities of servo information The read and wπte head 22 is a small assembly provided on the end of an arm or transducer assembly 24 that moves the head 22 over the storage surface 10 The transducer assembly may move the head 22 by rotation, by translation or by a combination of rotations and translations For example, many present dπves provide larger movements by rotating the transducer assembly about a pivot on the end of the transducer assembly opposite that of the head 22 Additional adjustments may be accomplished using fine translations, which might be accomplished, for example, using piezo-electπc elements In general, the mechanical rotational and translational movements of the head 22 are preferably accomplished under servo control using, for example, speaker motors or other compact, fast response systems The read and wπte head 22 of the transducer assembly is typically not πgidly attached to the transducer assembly Rather, the read and wπte head is preferably mounted on a slider coupled to the transducer assembly through a flexible assembly Typically the slider is designed to "fly" on an air beaπng over the data storage surface created between the shaped undercarπage of the slider and the disk

FIG 2 illustrates in greater detail aspects of one currently favored read and wπte head design The illustrated read and wπte head 22 is mounted on one end of a slider 26 that is, in turn, mounted to the transducer assembly (not shown in FIG. 2). A magnetoresistive read element 28 is formed as a thin film element near or on the end surface of the slider and then an inductive or other type of wπte element 30 is provided partially over the read element 28 A protective coating 32 covers the read and wπte head 22 As illustrated, it is typical that the wπte element 30 is considerably larger (sometimes 160% or more) than the read element 28 In addition, the read element 28 is typically offset to one side with respect to the wπte element This configuration is characteristic of magnetoresistive elements and causes the read and wπte head to have different preferred positions with respect to a track or other data storage structure for respective read and wπte operations

A read and wπte head 22 associated with a storage surface is precisely positioned with respect to data storage locations along a track through the use of servo control mechanisms within the disk dπve that operate m conjunction with positional servo information stored on the storage surface of the disk dπve Vaπous servo schemes have been used histoπcally for magnetic storage disk dπves, with the industry presently preferring the use of buπed servo information included on each data storage surface on the disks within the disk drive In reliably performing a track seeking operation, the disk dπve uses the read element 28 of the head to detect servo position information that is used by control circuitry to position the transducer assembly and the head over the target track The servo position information identifies the centerlme of each track and provides at least a relative identification for each of the tracks on the disk drive.

Positional control or servo information most often is stored within radially extending sector servo wedges, described in greater detail in the above-referenced patents, precisely placed on the disk's data storage surface during the original manufacture of the disk storage device. The positional and other servo information may be stored with a servo writer like that described in U.S. Patent No. 4,920,442 or in accordance with the methods described therein. Servo writers are used in a factory initialization process to write positional and other servo information on the storage surfaces of the disks, along with other information to prepare the storage surface for use. The servo writer, typically using precise positional information provided by a laser positioning mechanism, most often places servo information on each track along predefined radial spokes, defining the beginning of each sector on the disk.

FIG. 1 shows two possible organizations of servo information on the storage surface of a disk 8, the one discussed above in which full radial wedges 34 extend over the usable radial extent of the data storage surface 10 and another in which partial servo wedges 36 are provided in different densities in different zones of a storage surface. In the first method there may be on the order of 100-200 servo bursts positioned at regular angular intervals on the storage surface of a 3.5" storage disk. Different designs and operational parameters can change these characteristics significantly. In the second of the methods, there is an increasing number of servo wedges in each of the zones as they progress away from the center of the disk. Generally, only one of the two schematically illustrated methods is used on a disk.

Regardless of whether zones are differentiated on the data storage surface, the servo wedges may include a significant amount of information useful for positioning the head and for reading and writing data to the disk. An exemplary illustration of the information that may be included in the servo wedge is provided, for example, in previously incorporated by reference U.S. Patent No. 5,796,543 and is reproduced in FIGS. 3a and 3b, which respectively illustrate writing and reading operations. These figures show a portion of a servo wedge 40 where it extends across four data tracks Tr 0, Tr 1, Tr 2 and Tr 3. The wedge 40 is made up of a servo preamble 42 and servo position information 44 and the wedge is followed by one or more data blocks 46 in each of the tracks. A head 22 including both read and write elements is shown to indicate the procession of data (leftward) by the head and the preferred position of the head with respect to the centerlme of the track dunng wπtmg (FIG. 3a) and reading (FIG. 3b) operations. As shown, the read element is typically maintained off the center line by a predetermined displacement dunng a wπte operation. Because of this, the preferred track following position is sometimes off of the centerlme of the track.

The servo preamble 42 provides information used to adjust the read channel electronics for reading and processing the positional servo information The servo position portion 44 of the servo wedge provides the actual position data to be read by the read element 28 and used for positioning the head 22. The illustrated servo preamble 42 begins with a pre-burst gap 48 in which no transitions are recorded followed by an automatic gam control (AGC) field 50 that might include a regular pattern of transitions (e g , a positive 3T pattern followed by a negative 3T pattern) used to adjust the gain of the read channel electronics The servo preamble next includes a sync pattern 52 for setting the clock in the read channel electronics when leading the servo positional information, which may be followed by a servo address mark 54 that indicates to the read channel electronics that the subsequent information will be servo positional information, as opposed to data Next the servo preamble 42 may include an index field 56 that provides positional information within the track, i e , whether the servo wedge is that designated as the first servo wedge on the track. After the servo preamble 42 is the servo position information 44, including coarse position information 58 and fine position information 60-66 The coarse position information 58 may, for example, compπse Grey codes that numeπcally designate each of the tracks on the storage surface Generally, a gap separates the coarse position information 58 and the finer track positioning information provided by servo bursts 60-66. The checkerboard pattern 60-66 of offset servo bursts A, B, C, D of recorded information are written to have precise and desired positions with respect to the centerhnes of different tracks withm a predetermined grouping of tracks This allows the read element to generate a control signal related to the linear offset with respect to a desired position relative to a track, such as the track centerlme, which control signal can be used to adjust the position of the head with respect to the track

The illustrated checkerboard pattern consisting of the A, B, C, D servo bursts is formed by a servo wπter using multiple wπte and erase passes dunng manufacture so that each of the servo wedges includes the illustrated pattern of four rectangular servo bursts repeated at desired radial and tangential positions. The servo bursts A, B, C, D might internally consist, for example, of a repeating 3T pattern, with the servo bursts surrounded by regions without recorded transitions In the normal operation of the disk dnve, the boundaπes of the servo bursts are detected in track seek and track following operations to penodically generate a position error signal (PES) that can be used to adjust the position of a head with respect to a data track. In between the servo bursts, multiple (typically 3-5) data blocks are stored along the track. The servo control mechanism works in cooperation with the buπed servo information to place the head accurately at a desired position with respect to the track as the servo burst passes beneath the head. No additional positioning information is available until the next servo wedge passes by the head Accordingly, the servo control mechanism attempts to hold the head in a fixed position with respect to the track position identified by the most recent servo burst It is possible for the head or the disk to move due to mechanical impacts, vibrations, thermal variances or other disturbances in the system before reaching the next servo burst.

In addition to the track identification information within the servo wedge, storage surfaces are sometimes provided with additional information to indicate when the desired track and sector has been located in a seek operation An ID header block may optionally be provided between the servo burst and the first data block of a sector. The ID header pnmaπly includes identification for the track and the following sector Aspects of the use of synchronization patterns and headers are descnbed. for example, m U S. Patent No. 5,541,783 and U S. Patent No. 5.796,534, which patents are hereby incorporated by reference While header information may be provided at the start of sectors in many systems, other techniques for identifying tracks that do not use headers are known. For example, ID and header information can be included within the servo bursts as descnbed in the article by Fmch, et al , "Headerless Disk Formatting Making Room for More Data," Data Storage (Apπl 1997), pp. 51-54, or servo information can cross-reference information stored in a corresponding table in memory as descnbed in the IBM Storage publication by Hetzler, "No-ID Sector Format," dated January 8, 1996.

Following a servo wedge 40 (and ID header block when used), multiple blocks of data (typically 3-5) can be stored along a track, as shown m FIG. 4 Each block of data 70, 72, 74 includes a data synchronization pattern 76, 78, 80 positioned adjacent the data storage region of the block. Typically, a data block 70, 72, 74 is followed by an ECC block 82, 84 that stores error identifying and correcting codes for the preceding data block. The data storage region of each data block is typically of sufficient size to store data signals to represent 512 bytes of data. The data synchronization pattern includes synchronization information that can be extracted to establish a sampling frequency and phase for recovenng data stored from a data storage region The conventional synchronization pattern 76, 78, 80 is wπtten by the wπte element of a head in an operation m which the associated data block 70, 72, 74 is wntten. The clock rate used to wπte the synchronization pattern is also used to wπte the subsequent data blocks. Dunng a subsequent read operation, the read element of a head passes over the synchronization pattern and detects a pattern of transitions (e g , a 2T or 3T pattern) from which a clock is deπved for reading the subsequent data blocks. Conventionally it is prefened that the synchronization pattern be substantially uniform in the radial direction, varying only in the tangential direction for a read element positioned in a desired manner with respect to the track. Typically, the disk control logic and the actual rotational speed of the disk determine the data rate wπtten for the data synchronization pattern and the data storage region that follows Accordingly, the actual data rate can vary from block to block and sector to sector and, consequently, the amount of space occupied by the stored data can change To accommodate these changes, there is typically a gap (an interblock gap) or data pad 86, 88 following each data block to insure that there is sufficient physical separation between successive blocks along a track to allow data blocks to be written without overwntmg a subsequent block header or trailing servo burst.

There is a tension in designing data storage systems between increasing the track density, which typically requires denser servo wedge patterns, and loss of storage area due to the provision of increased densities servo information. It is desirable to provide additional servo information without reducing the area on the data storage surface devoted to the actual storage of data. In other words, it is desirable to increase the storage density without increasing the overhead necessary for accurately stoπng and retπeving information SUMMARY OF THE PREFERRED EMBODIMENTS

An aspect of the invention provides a data storage system with a data storage surface having a track compnsing adjacent data storage locations positioned along the track Data are stored along the track and are readable by a read head appropπate to the data stored on the data storage surface The track includes one or more synchronization patterns readable by the read head, where the synchronization pattern represents a clock signal provided to facilitate the recovery of data from the plurality of data storage locations The synchronization pattern further includes servo information readable by the read head, the servo information indicating a position with respect to the track

Another aspect of the invention provides a data storage system, the system compπsmg a data storage surface having a track compnsing adjacent data signal pattems, where the data signal patterns are readable by a read head and appropnate read channel electronics to provide data The track includes one or more synchronization patterns readable by the read head and the appropπate read channel electronics to provide synchronization information to facilitate the recovery of data signal patterns from the storage surface The synchronization pattern also includes servo information readable by the read head and the appropπate read channel electronics The servo information indicates a lateral position with respect to the track Another aspect of the present invention provides a data storage system with a data storage surface having a first plurality of substantially concentπc tracks Each track includes adjacent data signal patterns readable by a read head and appropnate read channel electronics The data storage surface includes a synchronization pattern extending across a second plurality of tracks, the synchronization pattern readable to provide a clock signal, the data signals from a data storage region adjacent the synchronization pattern readable in accordance with the clock signal The synchronization pattern also has servo information readable to indicate a lateral position with respect to the track

Still another aspect of the present invention provides a data storage system, compnsing a plurality of platters each having at least one data storage surface having a plurality of substantially concentnc tracks, with each track compnsing data signals A plurality of arm assemblies are provided in the system, with at least one arm assembly provided for each data storage surface Each arm assembly has a read head and an actuator for laterally positioning the read head with respect to one or more tracks on the data storage surface. Each track has a data storage region compπsmg a plurality of data signals and an associated synchronization pattern extending laterally across at least one track. The associated synchronization pattern is readable to provide a clock signal charactenstic of the data signals of the data storage region The synchronization pattern further includes servo information readable to indicate a lateral position of the read head with respect to the track being read. When a read head is positioned over a track to be read, the actuator adjusts a lateral position of the read head with respect to the track at least partially due to the servo information included within the synchronization pattern

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention, along with the vanous attendant benefits related to use and practice of these aspects, may be better understood with reference to the drawings, which form a part of the disclosure.

FIG 1 schematically illustrates aspects of a magnetic disk dπve, including a read and wπte head mounted on an arm and the data storage surface of a disk FIG. 2 illustrates aspects of read and wπte elements of a head FIGS. 3a and 3b illustrate information stored withm a sector servo wedge and the relationship between a head, the servo information and data tracks for wnte and read operations, respectively

FIG 4 illustrates aspects of the structure of data blocks withm a track FIG 5 schematically illustrates the spacing between tracks and a compaπson between well-wntten and badly-wπtten tracks. FIG. 6 illustrates aspects of a two-phase sync-servo pattern in accordance with the present invention

FIG. 7 shows the pattern of FIG 6 further including stored data FIG 8 shows a variation on the sync-servo pattern of FIG 6 consisting of three phases of servo information FIG 9 shows an exemplary apparatus using the sync-servo pattern of the present invention DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Compared to conventional wedge servo patterns, preferred embodiments of the present invention provide more servo information on a data storage surface so that a data head encounters servo information more frequently as the track or other data storage structure moves with respect to the head Most preferably, additional servo information is provided on the data storage surface without using space that would otherwise be used for data storage For example, preferred embodiments of the present invention might incorporate servo information withm the synchronization signals provided for each data block This might be accomplished in preferred embodiments by incorporating two dimensional, radial and tangential, vanations in the synchronization pattern so that the pattern provides both synchronization information and servo information Such a pattern can be formed without making the synchronization pattern larger or reducing the effectiveness of the synchronization pattern Synchronization signals are generally provided on data storage surfaces of disk dnves to establish a clock signal for reading data from a storage surface Typically, synchronization signals are provided for each data block, so that synchronization patterns occur several times more frequently than conventional radially extending sector servo wedges on a storage surface Moreover, synchronization patterns conventionally are functionally one dimensional, varying only along the tangential direction and not varying significantly in the radial direction on the scale of the area sensed by the read head Additional information can be provided along the radial direction within the synchronization patterns without impainng the effectiveness of the synchronization pattern Because the synchronization pattern is typically provided near, if not adjacent the data storage region of a data block, the synchronization pattern is m an advantageous position to provide positional servo information for reading data from a data block By providing servo information within the synchronization pattern for each of the data blocks provided between the servo wedges along a track, a read head or a wπte head position can be detected and adjusted with respect to the track with significantly greater frequency, improving the head positioning for both read or write operations This increase in positioning accuracy for read and wnte operations is desirable for a vaπety of reasons, including the fact that it facilitates the use of higher storage densities in future disk designs FIG 5 illustrates the differences between precise positional control dunng a wnte operation and poorer positional control dunng a wnte operation, such as might occur for a data block displaced away from a sector servo wedge when the disk is subject to vibration The figure shows a data block withm a well-wntten track 90 where the wntten data is symmetπcally disposed about the centerlme of the track The wπte width of the track (TW) is symmetncally disposed withm the pitch allowed for the track TP For a well wπtten track 90 such as is illustrated, a read head centered on a track senses a read area 92 positioned within the data stored on the track with good margins between the read area 92 and the edges of the wntten track area The track arrangement might, for example, illustrate a track pitch TP of 1 0 μm, a wπte width TW of 0 8 μm, and a read width 92 of 0 6 μm

In contrast to the ell-written track 90. the badly-written track 94 is subject to poor positional control and mechanical disturbance The path of the badly-wπtten track vanes within the track pitch in an megular manner It is possible for such an irregular wπte path to be sufficiently misaligned that the read width is partially off of the wπtten area, as indicated at 94 Such a misalignment reduces the quality of the read out data and can lead to read errors To avoid this problem, it is conventional to increase the size of the wπte width relative to the read width A different error, indicated at 96 in FIG 5, occurs when a wnte head becomes misaligned to a sufficient extent to overwnte the wπtten area of an adjacent track Such an error is extremely undesirable and is avoided by increasing the track pitch

Each of the potential errors illustrated in FIG 5 is addressed by increasing the spacing between structures withm the track Because of this, improvements in head positioning accuracy can be significant factors in improving the density of tracks and wπtten information

Position control for a head with respect to a track on a storage disk is improved using a synchronization or sync pattern that includes servo information as well as synchronization signals of the type used conventionally in recovenng data from a disk A conventional sync pattern might include a set of magnetic signals that vary along the length of a track and do not vary appreciably across a track In accordance with preferred embodiments of this invention, servo information, suitable for identifying a misalignment between a head and a track is added to this conventional synchronization pattern by modulating the conventional synchronization pattern with a two dimensional servo pattern that includes information about a position or lateral offset of a head with respect to a track. The combined pattern might include relatively rapidly varying sync signals covenng square or rectangular regions of the storage surface. The bursts of sync signals preferably have dimensions on the order of the size of a track and are arranged to have a lateral boundary withm the width of an associated track Adjacent regions of the storage surface preferably are square or rectangular regions with no or substantially no sync signals The bursts of sync signals and the rectangles without servo signals are arranged in a larger-scale two dimensional pattern The larger-scale two dimensional pattern provides the servo information in the combined sync-servo pattern in a manner generally similar to conventional wedge servo patterns

Most preferably, combined sync-servo patterns are provided in addition to the conventionally provided radially extending sector servo patterns A preferred synchronization pattern in accordance with the present invention may include a seπes of signals extending along a track that may constitute a clock signal or another synchronization signal suitable for setting the frequency and phase of a phase locked loop detector or other synchronized detection scheme For convenience, a synchronization pattern in accordance with the present invention that combines the servo information of a servo pattern withm a synchronization pattern is referred to here as a sync-servo pattern A sync-servo pattern preferably includes servo information in the form of radially displaced components, considered relative to a nominal position with respect to a data track such as the track centerlme The relative positions of the vanous bursts of sync signals with respect to the data tracks provide servo information As shown in FIGS 6-8, the two dimensional nature of this pattern can be detected by a read head passing over the sync-servo pattern Of course, the synchronization pattern within the larger-scale pattern preferably precisely maintains the relative location of each clock signal or transition along the data track, / e , the tangential position along the track, to provide an accurate data detection clock

Detection of the radially varying attnbutes of a sync-servo pattern allows generation of a head position error signal Concunently, the tangentially varying attnbutes of the sync-servo pattern can be used to generate a clock signal m-phase and of an appropnate frequency to recover data from the data storage region of a data block By using a synchronization pattern that combines both radially and longitudinally displaced attnbutes, the functions of a servo burst and a synchronization pattern are combined into a single, sync-servo pattern Since this combined pattern preferably is used for each data block, a higher frequency position error signal is generated, facilitating an improved overall tracking of the read and wπte head over a target data track

As discussed here, data are wπtten to a disk using a wnte element and data are read from the disk using a read element, where both the wnte and read elements are typically provided on a single head For most of the considerations here, the invention can be discussed in terms of a read head or, more geneπcally, a head Use of one term or another is not intended to limit the invention

For the purposes of this invention, a synchronization or sync signal is a signal on or associated with a data storage block having a generally repeating pattern that can be detected to recover a clock or timing signal charactenstic of signals stored in the data block The pπmary example of a synchronization pattern presented here is a non- return-to-zero pattern, but other sync signals have been used and might be used in the future

For the purposes of this invention, a servo signal or pattern is a signal or collection of signals varying as a function of position on a storage surface to a sufficient level on the scale of a track or other data storage structure to allow use of the servo signal or pattern in an automatic control system More specifically, a servo signal or pattern is a pattern varying laterally or radially on a circular disk that is detectable by a read element to indicate a position or offset of the read head The detectable signal preferably vanes sufficiently to allow an automatic feedback control system to determine and adjust a read head position with a desired level of accuracy with respect to a desired position on a data track A sync-servo signal or pattern is one which, m whole or m part, facilitates both synchronization and servo functions

This specification now discusses preferred aspects and advantages of the present invention in still greater detail with reference to the drawings

In initially preferred embodiments, the sync-servo pattern is used in conjunction with a conventional servo pattern like that illustrated in FIG 1 FIG 1 shows a conventional arrangement of sector servo wedges 34 on the data storage surface of a disk 8 These servo wedges 34 are positioned dunng manufactunng along radial spokes from the center of the disk extending through the data tracks on the data storage surface. Each data track can include multiple data blocks 70, 72, 74 as shown in FIG. 4 Due to the different circumferences of each data track and other factors (e g , zones), more data blocks are placed on the outermost data tracks than on the innermost data tracks Accordingly, the number of data blocks located between servo wedges is greater on outermost tracks (typically 5 data blocks) than on innermost tracks (typically 3 data blocks) Most preferably, the data blocks 72, 74 (FIG. 4) separated from the sector servo wedges 40 (FIG. 4) by at least one other data block are provided with a sync-servo pattern in accordance with the present invention. The data blocks 70 positioned adjacent the servo wedges 40 have less need for servo information, but still need sync information Consequently, certain embodiments of the invention provide a sync-servo pattern for data blocks 70 adjacent sector servo wedges 40. fn other embodiments, though, data blocks 70 immediately adjacent a sector servo wedge might not include a sync-servo pattern and might in fact rely on clock synchronization from the sector servo wedge for wnting and reading data. As previously discussed, multiple data blocks are located on each track following each sector servo wedge. Each data block includes a data synchronization pattern for specifying the date rate for the data block The physical size of each data block is determined by a wπte clock in the disk dnve electronics as well as the rotational speed of the disk dunng the wπte operation While efforts can be extended to control both of these factors, e.g., by using higher precision (and higher cost) oscillators and related signal processing techniques, the physical size of each data block remains in most practical applications somewhat vanable Thus, to accommodate up to 5 data blocks between the precisely positioned servo wedges, conventional recording systems typically provide extra, unused track space (e g , an interblock gap) to accommodate these vanations. The interblock gap (86, 88 in FIG. 4) following each data block insures that there is sufficient physical space on each track to allow blocks to be wntten without overwriting a subsequent data block or servo information. There are more interblock gaps on the outermost tracks than on the innermost tracks since there are more data blocks on the outermost tracks Typically, there is more unused space on the outermost tracks.

Some embodiments of the invention reduce the size of gaps between data blocks by allowing data blocks to be split between different sectors. Said differently, m these embodiments portions of one data block might be positioned on either side of a sector servo wedge. In such a case, the portion of the data block positioned on the trailing edge of the servo burst is preferably provided with a synchronization pattern but it is generally not desirable to provide servo information withm that partial data block sync pattern. Embodiments of the present invention use a synchronization pattern incorporating servo information that either supplements or replaces conventional sector servo bursts by providing a data synchronization pattern also having aspects of a servo pattern to provide an integrated sync-servo pattern 100 (FIG. 6) The sync-servo pattern 100 is formed, preferably dunng manufacture, as a two-dimensional pattern having radial and tangential extents, respectively used pnmanly for head to track alignment and data clock synchronization Since this sync-servo pattern 100 can be formed using technology similar to that of a conventional servo wnter, both of these aspects are most preferably precisely controlled and created dunng manufacture of the disk. A sync-servo pattern 100 is wπtten for most, if not all, data blocks. Accordingly, a higher frequency position enor signal results, which provides higher levels of head to track alignment and reduces the requirements that overly wide (radially) data signals need be wntten. This can lead to high wnte densities for data, taking advantage of the greater head to track alignment for each track.

FIG. 6 shows an exemplary implementation of the sync-servo pattern 100 of the present invention Preferably, the sync-servo pattern 100 is formed on the surface of a disk platter dunng the manufactunng process, e g , typically using a servo wnter or equivalent The servo wnter precisely controls the phase and data clock rate, i e , the tangential phase and clock rate at which data are stored on each track (t e., the physical displacement between data bits) and additionally uses a laser positioning mechanism to precisely form the sync-servo pattern over the width of each data track. The sync-servo pattern 100 compπses synchronization or clock signals having two aspects. In a first aspect, a pattern is formed from a plurality of synchronization signals, where groups of synchronization signals are positioned to have radial displacements from a nominal track position such as the illustrated centerhnes This aspect can be detected in a manner similar to conventional servo to determine a signal indicative of the position error signal between the present head position and the track. An exemplary servo signal Vs is shown in FIG. 6 In a second aspect, the longitudinal displacement between matched phases of the synchronization signals specifies a data rate for subsequently wπting data signals into the following data storage region, as discussed below Most preferably, the sync signals stored m this manner are non-return-to-zero (NRZ) signals (e g , 1 1001100110011) or a similar appropπate clock pattern It is preferred that the synchronization pattern be coextensive with the servo pattern, so that the entire pattern has a constant longitudinal displacement between each data bit in the sync-servo pattern 100 to store as much synchronization information as practical It is nevertheless possible to restπct the synchronization information to a limited portion of the sync-servo pattern 100, e g , only the servo signal region positioned closest to the data storage region Either approach is considered to be within the scope of the present invention, although the more complete synchronization information of the coextensive embodiment has the advantages discussed above

In the exemplary implementation of FIG 6, a first set of synchronization signal bursts 106 is stored offset in a first direction with respect to a defined position on each of the tracks (nominally the centerlme) A second set of synchronization signal bursts 108 is stored offset from the desired positions with respect to the array of tracks in the opposite direction from the first plurality of sync-servo data bits 106, e g , below the track centerhnes Preferably, synchronization signal regions compnse a plurality of synchronization bits with succeeding synchronization bits within bit values switching every other bit position, t e , a 1 10011001 1 (NRZ) pattern is preferably used When a read element of a head is positioned over a sync-servo pattern 100 such as that illustrated in FIG 6, the detected position error signal can reflect the position of the head with respect to the track centerlme or other designated track reference point The read element of the head detects amplitudes V_A and V_B corresponding in amplitude to the fraction of the conesponding A and B sync-servo burst patterns covered by the head 212's read width By processing the difference in magnitude between signals V_A and V_B a position error signal Vs is generated which reflects the magnitude of the head to track displacement Furthermore, since this error signal is available for each sector, a position error signal having a higher frequency than conventionally available preferably is achieved Preferably, signal 114 is processed by a device (referred to herein as a servo extractor) and this processed signal is used to identify and preferably correct, whether in a track seeking operation or as a fine control in tracking, a head to track positioning error.

The tangentially varying components of the sync-servo pattern 100 are spaced essentially constantly along the track. Accordingly, reading the sync-servo pattern 100 with a read head produces AC components having an essentially constant frequency. These AC components correspond to the clock rate for the data block (or alternatively to an integer division of the clock rate, e.g , Vι of the clock rate) Preferably, the detected AC signal can be processed by a device referred to herein as a sync extractor, e.g , a phase locked loop, and the resulting sample clock can be used to facilitate extracting data from the data block Additionally, this clock preferably is also used as a wnte clock for storing data into the data block. Since the wnte clock is then based on the clock stored in the sync-servo pattern, the data can be stored with the desired level of precision.

In accordance with prefened embodiments of the present invention, the sync- servo pattern 100 of the present invention allows reduction in the mtertrack separation or track pitch, i e , the distance between the tracks of data, because the servo position control capability is improved.

Following the sync-servo pattern 100, a data block 138 (FIG. 7), which may consist of 4096 bits or 512 bytes, can be wπtten In a wπte mode, a system incorporating certain aspects of the present invention reads the preferably factory- wntten sync-servo pattern 100 to position the read/wnte head and extract a timing signal to adjust an internal wπte clock The system preferably then switches to a wnte mode and begins wnting data at a predetermined time or after a number of counts that designates the end of the synchronization pattern Since the synchronization pattern is of precisely determined length, the beginning of the wnte operation can be determined with high accuracy, allowing the wπtmg to begin without damaging the factory- wntten sync-servo pattern 100 In some embodiments, it may be desirable to provide a gap between the synchronization pattern and the data storage region of the data block. Other embodiments might record an additional field between the sync-servo pattern and the data block, such as an address mark

Most preferably, the data stored in accordance with preferred embodiments of the present invention are encoded using partial response maximum likelihood (PRML) encoding. Additionally, a run length limited (RLL) or other encoding technique might be used for encoding the data stored in the data storage region. Following writing of the data block, an interblock gap may be provided following the data block 138 (including enor codes, if any) and before the next signal region, preferably the sync- servo pattern associated with a next subsequent data block. Due to the increased precision in head positioning and the clock repeatability, the interblock gap can be reduced as compared to the conventionally provided interblock gap.

It is preferable to include identification information (ID), e g , header information, to confirm or facilitate locating a target track and a data block in the manner illustrated in FIGS. 3a and 3b of this application. In an exemplary ID block, data are included that represent the track and data block and, optionally, other information such as whether the block associated with the header is defective. In some preferred embodiments, an ID block is included withm each sync-servo pattern 100, preferably at a leading edge pnor to the track alignment and synchronization patterns are provided. Alternatively, the ID block can be included within portions of the data blocks on each track For example, if the ID block were present for one out of every five data blocks, disk control logic would, at worst, only need to recognize a pnor data block from its ID block and count blocks (up to four times) until the desired sector was reached. In another implementation, the teachings of aforementioned IBM bulletin ("No-ID Sector Format" by Dr. Steven R. Hetzler of the IBM Research Division, dated January 8, 1996), previously incorporated by reference, might be used to eliminate the need for an ID block

As previously discussed, certain embodiments of the present invention have a sync-servo pattern 100 inserted at the beginning of each data block and thus need not provide a separate sector servo burst wedge. In other words, it is possible to use the illustrated sync-servo patterns as the only positional servo information on a disk surface. On the other hand, other preferred embodiments of the invention provide both a conventional sector servo pattern 34 such as that illustrated m FIG. 1 along with the sync-servo pattern 100 discussed herein. Regardless of the precise overall configuration, an integrated sync-servo pattern 100 can provide significantly better tracking due to the higher density of servo information, as compared to the conventional sector servo pattem that uses only servo bursts 34 (shown in FIG. 1) occurring every three to five data blocks. The advantages related to this distinction are even more apparent when the concept of zones is considered. Since the circumference of each track decreases as the radius of the track decreases from an outermost track to an innermost track on a disk, the same amount of data cannot be reliably stored on each track Conventionally, the innermost tracks store less data less efficiently than do the outermost tracks For example, the outermost tracks might store two hundred sectors or more, while the innermost tracks may store only about 120 sectors These are of course only current figures and are expected to change over time

This problem is addressed by separating the disk into zones extending over different ranges of radii, as shown at 16, 18, 20 m FIG 1, with an equal number of data blocks per track preferably maintained for groups of tracks within designated zones A zone may be thought of as a band of tracks, extending between a first and second radius The same number of data blocks are provided m each zone of tracks positioned radii By providing a sync-servo pattern for each data block, different zones have corresponding and desirable densities of servo information Consequently, practice of preferred embodiments of the present invention provides a substantially improved and relatively uniform level of head to track positioning accuracy

FIGS 6 and 7 both show a two phase servo pattern made up of A and B subpatterns of sync-servo bursts Each of the offset patterns A, B consists of a seπes of closely synchronized clock signals such as NRZ signals having readily detectable amplitudes or transitions above a threshold level No signal regions, or regions having a below threshold signal level are provided within each of the A and B servo patterns to create the illustrated and prefened two dimensional sync-servo pattern Such patterns can be created using known servo wntmg techniques, except that it is prefened that a higher level of clock synchronization be used in wπting the sync-servo pattern so that a high level of synchronization is maintained over the width and length of the sync-servo pattern It is desirable to maintain a constant phase for the clock signal over the sync-servo pattern For example, the phase of the clock signal may be maintained constant within about 20° over the width of the sync-servo pattern, that is the entire radial extent of the servo pattern extending across as many tracks as are crossed As shown, the A servo subpattern consists of signal regions offset to one side of the track with no signal regions positioned on the opposite offset side of the track The B servo subpattern consists of no signal regions offset to the one side of the track with signal regions positioned on the opposite sides of the track In the A and B servo subpatterns, the lateral boundaπes between the signal and no signal regions he withm the tracks, although the precise position is not important Each of the A and B servo subpatterns has a preferred signal region width of approximately two-thirds of the width of a track pitch Alternately, the signal region width might be set to the size of the read region for the head In any case, it is particularly preferred that a read element passing over the sync-servo pattern consistently be over at least part of a signal region This allows the control system to receive a preferred continuous stream of clock or other synchronization signals from the sync-servo region

As shown in FIG 6, a servo (error or positioning) signal Vs can be deπved from the illustrated servo pattern V_s provides a linear error signal that can be used in a control system to cause an actuator to adjust the position of a head with respect to a position withm the target track Many different procedures can be used to implement a control algonthm with respect to the illustrated servo signal V_s, whether to perform track seeking or track following Implementation of particular algoπthms for these tasks is well within the skill of the ordinary artisan and so is not discussed further here FIG 7 shows the sync-servo structure in which data are stored in the defined data storage regions The FIG 7 embodiment provides a short gap between the end of the sync-servo pattern and the stored data region, as discussed above

The exemplary sync-servo pattern illustrated in FIG 6 has some inadequacies when used as the only head to track positioning or control signal An error signal or a head to track displacement signal that might be obtained using the servo pattern of FIG 6 is indicated as V When the head is centered on a track, the value of enor signal V is zero It can be seen, however, that the signal Vs has another zero at the midpoint between track centerhnes This midpoint zero can be detected in a large displacement operation such as a track seek and could possibly be selected as being within the target track rather than being recognized as between tracks It is consequently possible when using a servo pattern like that illustrated m FIG 6 for the control system to begin tracking a position between tracks Such an ambiguous tracking function is unstable, but not immediately so Consequently, a control system can cause a head to track such an ambiguous, halfway position for at least a short peπod of time, which can diminish performance

The possibility of enteπng this ambiguous tracking state does not impair the utility of the FIG 6 servo pattern for small displacement control functions This means that the FIG 6 servo pattern is completely adequate for track following functions Ambiguities can occur when larger displacement actions are performed, such as in a track seeking operation There are vanous ways to make the FIG 6 servo pattern immune to this ambiguous state Most simply, the illustrated sync-servo pattern can be used in conjunction with a conventional sector servo pattern, which provides sufficient additional information to preclude the between-track position from being selected for tracking

The combination of a sync-servo pattern with a sector servo pattern represents a particularly preferred embodiment of the present invention, because the provision of a higher density of servo information improves the overall positioning accuracy while retaining general consistency with presently prevalent technology This is accomplished without impacting upon the density of conventional disks By simply altenng the way that a conventional synchronization pattern is wπtten and altenng the head positioning control methodology to accept and utilize the additional positioning information, an improved level of tracking accuracy can be obtained without significantly increasing cost

Other adaptations of the FIG 6 sync-servo pattern can also remove the potential midpoint tracking ambiguity descnbed above A particularly preferred embodiment of an unambiguous servo pattern is the modification of the FIG 6 pattern illustrated in FIG 8 FIG 8 shows a three phase servo pattern within a sync-servo pattern in accordance with aspects of the present invention In other words, three offset svnc-servo burst patterns A, B, C are provided on the disk, with each of the offset patterns created by a senes of closely matched and synchronized clock signals such as NRZ signals having readily detectable amplitudes above a threshold level No signal regions, or regions having a below threshold signal level are provided within each of the A, B and C burst patterns to create the illustrated and particularly preferred two dimensional burst pattern Such patterns can be created using known servo wnting techniques, except that it is preferred that a higher level of clock synchronization be used in wnting the sync-servo pattern so that a high level of synchronization is maintained over the width and length of the sync-servo pattern It is desirable to maintain a constant phase for the clock signal over the sync-servo pattern For example, the phase of the clock signal may be maintained constant within about 20° over the width of the sync-servo pattern, that is the entire radial extent of the servo pattern extending across as many tracks as are crossed.

As shown, the A sync-servo subpattern consists of signal burst regions positioned to one side of the track with no signal regions offset in opposing fashion. The B sync-servo subpattern consists of no signal regions positioned to the one side of the track with signal regions positioned on the opposite sides of the track as illustrated. In the A and B sync-servo subpatterns, the boundaries between the signal and no signal regions lie within the track, for example, near its center. The third phase of the servo pattern is the C sync-servo subpattern, which consists of signal regions centered on the tracks. Each of the A, B and C sync-servo subpatterns has a preferred signal region width of approximately two-thirds of a track pitch. Alternately, the signal region width might be set to the size of the read region for the head. In any case, it is particularly prefened that a read head passing over the sync-servo pattern constantly be over at least part of a signal region. This allows the control system to receive a preferred continuous stream of clock or other synchronization signals from the sync- servo region.

As shown in Fig. 8, three different servo (error or positioning) signals V₀, Vj, V₂ can be derived from the illustrated servo pattern. V₀ corresponds to the Vs signal discussed above with respect to the FIG. 6 servo pattern and can be used in the same way. Note that the previously ambiguous halfway position between the track centerlines can be positively resolved using either of the V] or V₂ servo signals. Many different procedures are apparent for using the servo signals V , Vi, V₂ to perform track seeks and track following. Implementation of particular algorithms for these tasks is well within the skill of the ordinary artisan and so is not discussed further here. FIG. 9 shows an exemplary apparatus 200, a hard disk drive, that uses the sync- servo pattern 100 of the present invention. As previously described, a plurality of sync-servo patterns (one per data block) are preferably written onto the face 202 of one or more platters 204 of the hard disk drive 200 during the manufacturing process. Only one face of a single platter is shown for illustration purposes. The hard disk drive 200 receives commands to access a track and data block of the hard disk drive 200 via an interface 206. An onboard controller 208, e.g., a microcomputer, instructs a position controller 210, e.g., a servo controller, to position a read/write head 212 over the designated track. As the platter 204 spins along axis 214, a signal 216 is generated by the read portion of the head 212 which corresponds to one of the prerecorded sync-servo patterns 100 A servo extractor 218 processes this signal 216 and, according to the relative amplitude of portions of the signal, generates a position error signal 220 This position error signal 220 is used either directly by the servo controller 210 or indirectly (see dotted path 222 to controller 208) to perform a fine adjustment of the position of the head 212 with respect to the requested data track Preferably, an ID block is read from a portion of the sync-servo pattern 100 to confirm that the requested track has been found and, if not, the controller 208 can be instructed via path 224 to reposition to another track Additionally, the ID block preferably identifies the cunent data block and this information is used to determine when the requested data block has rotated under the head 212

Concurrently, a clock extractor 226 processes signal 216 to retneve a clock signal from the sync-servo pattern 100 Preferably, this clock signal, e g , the AC component of signal 216, is used in conjunction with a phase locked loop within the clock extractor 226 to generate a data clock 228 This data clock 228 is used in conjunction with a data extractor 230 to preferably extract PRML encoded data, e g , the ID block and the data signals within the data storage area This data is then provided via the interface 206 Alternatively, when a wnte command is received, a data encoder 232 (preferably using PRML encoding), uses the recovered data clock 228 to generate signal 234 to control the wnting of a data block following the processing of the sync-servo pattern 100 for the requested track and sector

Although the present invention has been descnbed in detail with reference only to the presently-preferred embodiments, those of ordinary skill in the art will appreciate that vanous modifications can be made without departing from the invention For example, while the disclosure has pnmanly discussed magnetic media, this invention's applicability to other rotational media (e g , read only, wnte once and re-wntable optical disks, etc ) and other data storage systems should be apparent to those skilled in the art Additionally, while an exemplary sync-servo pattern 100 has been shown, other patterns with include both radially offset and longitudinally offset patterns are also considered to be within the scope of the present invention For example, in the case of a read only device, both the data and the sync servo pattern could be concurrently written, e.g., stamped, onto an optical device. Accordingly, the invention is defined by the following claims.

Claims

What is claimed:

1 A data storage system, the system compnsing a data storage surface (10) having a track (46) compnsing adjacent data storage locations positioned along a length of the track, data stored along the track readable from the plurality of data storage locations by a read head (26) appropnate to the data stored on the data storage surface (10), the track including one or more synchronization patterns (100) readable by the read head, the synchronization pattern representing a clock signal provided to facilitate the recovery of data from the plurality of data storage locations, the data storage system characteπzed in that the synchronization pattern (100) further compnsing servo information readable by the read head, the servo information indicating a position with respect to the track

2 The system of claim 1, wherein the storage surface (10) is provided on at least a portion of a disk and the storage surface further comprises regularly spaced servo patterns (40) each extending over at least a portion of a radius of the disk, the regularly spaced servo patterns (40) provided at regular angular intervals on the surface of the

3 The system of claim 1 , wherein the servo information (106, 108) is provided withm a servo signal pattern extending over a portion of the length and at least a portion of a width of the track, the servo signal pattern compnsing signal regions and no signal regions

4 The system of claim 3, wherein the signal regions are characterized as having plural signal transitions and no signal regions are charactenzed as not having signal transitions

5 The system of claim 3, wherein the signal regions have a number of signal transitions above a threshold number and have signal transitions of a magnitude above a threshold level and wherein the no signal regions have undetectable signal transitions or signal transitions of a magnitude smaller than a threshold level

6. The system of claim 3, wherein a read head (212) passing over the servo signal pattern is always positioned over at least a portion of a signal region.

7. The system of claim 3, wherein the no signal regions, as measured along the width direction of the track, are narrower than a read head (212).

8. The system of claim 3, wherein the track has a centerline and wherein the read head passing over a centerline of a track

1. passes over a first portion of the servo signal pattern (106) with a first signal region offset to a first side of the centerline and a first no signal region offset to an opposite side of the centerline, and passes over a second portion of the servo signal pattern (108) with a second signal region offset to the opposite side of the centerline and a second no signal region offset to the first side of the centerline.

9. The system of claim 8, wherein the data storage surface (10) comprises a plurality of like tracks (46) positioned substantially concentrically on a disk shaped data storage surface, the tracks separated by a track separation measured radially between adjacent track centerlines, and the signal regions have a width, measured radially, of approximately two thirds of the track separation distance.

10. The system of claim 9, wherein the data storage surface further comprises second servo data (40) providing information to the read head about the read head's lateral position with respect to a corresponding centerline of any one of a group of radially adjacent tracks, the second servo data extending across the group of radially adjacent tracks in a series of radially extending spokes.

11. The system of claim 9, wherein the series of radially extending spokes (40) are positioned at regular angular intervals on the data storage surface and wherein a plurality of the synchronization patterns (76, 78, 80) comprising the servo information are positioned along one of the tracks in the group in addition to the second servo data.

12. The system of claim 1, wherein the clock signal is a regularly varying signal of substantially constant frequency and phase across the synchronization pattern (100), as measured along the length of the track.

13 The system of claim 1, wherein the data stored along the track is organized into groups (70, 72, 74), with each group associated with a respective synchronization pattern (76, 78, 80) on the storage surface so that, when data are read from a group, the respective synchronization is first detected to extract a clock signal

14 The system of claim 1. wherein the clock signal is a regularly varying signal of substantially constant phase across the synchronization pattem, with total vanations in phase of no more than 20° as measured along a radial line through the synchronization pattern cutting through all of the tracks that intersect the synchronization pattern

15 The system of claim 1. wherein the servo information is provided within a servo signal pattern (106, 108) defined within the synchronization pattern (100), the servo signal pattern compnsing first signal regions (106) and second signal regions (108) arranged over at least a portion of a length of the synchronization pattern (100), as measured along the track, and over at least a portion of a width of the synchronization pattern, the first signal regions (106) each extending in length over a plurality of individual synchronization signals within the synchronization pattern and the second signal regions (108) having a similar length, wherein signals denved from the synchronization pattern by a read head can distinguish between and the first and second signal regions

16. The system of claim 15, wherein the data storage surface (10) compπses a plurality of like tracks (46) positioned substantially concentπcally on a disk shaped data storage surface, the tracks separated by a track separation measured radially between adjacent track centerlines, and the first signal regions have a width, measured radially, of approximately two thirds of the track separation distance and the second signal region have a width, measured radially, of approximately one third of the track separation distance. 17 The system of claims 9 and 15, wherein the data storage surface (10) is one side of a platter within a multiple platter data storage system in which data are represented as magnetic transitions at least temporanly fixed in a magnetically alterable medium on the one side of the platter, the multiple platters of the system providing a first plurality of like data storage surfaces and at least a matching first plurality of read heads for reading data from the first plurality of like data storage surfaces

18 The system of claims 1-3 and 12-14, wherein servo information extracted from the synchronization pattern can be processed to provide an enor signal indicative of a relative lateral position of the read head with respect to the track being read

19 The system of claim 18, wherein the servo information is provided within a servo signal pattern (106, 108) extending over a portion of the length and at least a portion of a width of the track, the servo signal pattern compnsing signal regions and no signal regions, wherein a read head (212) passing over the servo signal pattern is always ove at least a portion of a signal region so that synchronization information is obtained continuously over the servo signal pattern

20 The system of claim 19, wherein the signal regions are characteπzed as having plural signal transitions of a measurable level above a threshold lev el and no signal regions are characterized as not having signal transitions