Patent Publication Number: US-8120868-B2

Title: Data storage medium having system data stored in a guard band between zones of consecutive data storage tracks

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. application Ser. No. 11/231,960 filed Sep. 21, 2005. 
    
    
     BACKGROUND 
     Data storage devices have tended to be made ever smaller, yet with ever greater storage capacity, as technology has been advanced. Many applications require “micro” data storage devices that are one inch or smaller in diameter, and a fraction of an ounce in weight, for example. Applications for which micro data storage devices are well suited include hand-held or otherwise easily portable devices, such as digital music players, PDAs, digital still cameras and video cameras, and external computer memory, for example. Adapting data storage technology with optimum performance in current applications poses considerable technical challenges. 
     Embodiments of the present invention provide unforeseen advantages over conventional data storage systems, and provide superior performance characteristics. 
     SUMMARY 
     Claimed embodiments are generally directed to servo formatting a storage medium. 
     In some embodiments a storage medium is provided having a first band of a plurality of consecutive data storage tracks having user data sectors stored thereto, a second band of a plurality of consecutive data storage tracks having other user data sectors stored thereto, and a guard track medially disposed therebetween the first band and the second band and having system sectors stored thereto. 
     In some embodiments a method is provided for processing data, including the step of retrieving system sectors from an annular guard band of one or more storage tracks that are interposed between and consecutive with a first band of a plurality of consecutive data storage tracks, having user data sectors stored thereto, and a second band of a plurality of consecutive data storage tracks, having user data sectors stored thereto. 
     In some embodiments a data storage device is provided having a storage medium that contains a plurality of different storage locations for storing user data. The storage locations include a minimum storage location and a maximum storage location that define extremities of a user data storage space continuum. The data storage device further has a means for optimizing a utilization of the storage medium by storing system sectors to storage locations within the user data storage space continuum. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a data storage medium with optimized servo format, according to illustrative embodiments. 
         FIG. 2  is a perspective view of a data storage system that may incorporate a data storage medium with optimized servo format, according to illustrative embodiments. 
         FIG. 3  is a close-up schematic of a section of a data storage medium with optimized servo format, according to illustrative embodiments. 
         FIG. 4  is a close-Lip schematic of a section of a data storage medium with optimized servo format, according to other illustrative embodiments. 
         FIG. 5  is a close-up schematic of a section of a data storage medium with optimized servo format, according to other illustrative embodiments. 
         FIG. 6  is a close-up schematic of a section of a data storage medium with optimized servo format, according to other illustrative embodiments. 
         FIG. 7  is a close-up schematic of a section of a data storage medium with optimized servo format, according to other illustrative embodiments. 
         FIG. 8  is a diagrammatic depiction of overlapping user data tracks used in conjunction with the optimized servo format, according to other illustrative embodiments. 
         FIG. 9  is a diagrammatic depiction of a section of a data storage medium with a plurality of bands of overlapping tracks and optimized servo format, according to other illustrative embodiments. 
         FIG. 10  is a diagrammatic depiction of a section of data storage medium with a plurality of guard bands according to other illustrative embodiments. 
         FIG. 11  is a schematic depiction of a servo sector format and a system sector format in illustrative embodiments. 
         FIG. 12  is a flowchart depicting steps in a power-on-reset routine in accordance with illustrative embodiments. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a plan view of a data storage medium  100  with an optimized servo format according to some illustrative embodiments. Medium  100  includes many inventive elements that provide substantial advantages in performance, as detailed with respect to  FIG. 1  and the remaining figures. For example, medium  100  provides advantageous performance by various inventive elements for optimizing its servo fields, such as servo bits written at higher frequency corresponding to greater radius, which provides reduced servo overhead and an increased proportion of data storage medium  100  devoted to storing data, for example. The servo fields occupy area on the medium  100  that is thereby removed from availability for user data, although the servo fields are advantageous in providing an associated read/write head with the information it needs to navigate the data tracks written to medium  100 . Some of the inventive elements of embodiments disclosed herein maximize the servo performance of the servo fields while minimizing the area of medium  100  that the servo fields take up. Various inventive elements are described in detail as follows below. 
     In particular, medium  100  includes different annular zones, such as the three zones  102 ,  104 , and  106  disposed generally concentrically on medium  100 , in the particular embodiment of  FIG. 1 . Medium  100  has an inner edge  136  and an outer edge  138 . The extremity of the user data storage space can be defined by the medium  100  as bounded by an inner extremity at an innermost user data storage track  137  and an outer extremity at an outermost user data storage track  139 . Zone  102  is adjacent inner boundary  136  and includes the inner extremity  137 , and may be considered the inner zone. Zone  106  is adjacent outer boundary  138  and includes the outer extremity  139 , and may be considered the outer zone, in these illustrative embodiments. With respect to the intermediate zone  104 , therefore, the inner zone  102  is a next inward zone from zone  104 , and the outer zone  106  is a next outward zone from zone  104 . A first annular guard band  142  is disposed between inner zone  102  and zone  104  and thereby nested between inner zone  102  and zone  104 , and a second annular guard band  144  is disposed between zone  104  and outer zone  106  and thereby nested between zone  104  and outer zone  106 . 
     Zones  102 ,  104  &amp;  106  are transected by a number of servo sectors, each composed of a series of servo fields, as illustratively and exaggeratedly depicted generally along illustrative servo fields  112 ,  114 ,  116  of servo sector  101 , and along other, similar servo sectors  103 ,  105 ,  107  disposed around medium  100 . Each of servo fields  112 ,  114 ,  116  radially spans one of zones  102 ,  104  &amp;  106 , with servo field  112  spanning zone  102 , servo field  114  spanning zone  104 , and servo field  116  spanning zone  106 , in these illustrative embodiments. By radially spanning the zones, each of servo fields  112 ,  114 ,  116  extends from a radially inward position in its respective zone, to a radially outward position in its respective zone. The actual servo sectors would be much smaller and narrower, and more plentiful, than in the depiction of  FIG. 1 , which has been exaggerated for clarity. Address marks extend radially from the inner diameter to the outer diameter within the servo zones, such as illustrative address mark  152  within servo sector  101 . Illustrative servo fields  112 ,  114 ,  116  include servo field bits written on medium  100 . The gaps  124 ,  126  adjacent servo fields  114 ,  116  are described below. The servo field bits may be written onto medium  100  during manufacture, with a specialized external write head, in illustrative embodiments. The servo fields may also be written in situ, in other illustrative embodiments. 
     Writing the servo bits to medium  100  involves rotating medium  100  while the write head writes one bit after another, in a selected frequency with which it writes new bits, with the inverse of the frequency being the period of time spent in writing each bit, in these illustrative embodiments. The servo frequency is typically less than the user data read/write frequency, in these illustrative embodiments. The servo bits thereby written to medium  100  each occupy a given arc length determined by the period expended writing the bit, times the rotation rate of the medium during the write, times the radial displacement of the position where the bit is written to the medium from the center of rotation of the medium. Therefore, if the same frequency is used for writing bits at different displacements from the center of rotation, a bit written at a greater radial displacement will also have a greater arc length than a bit written at a lesser radial displacement, in these illustrative embodiments. 
     In conventional devices, the frequency is set so that, during normal operation, a read/write head is able to read the bits with the shortest arc length, i.e. those at the smallest radial displacement from the center of rotation, adjacent the inner diameter of a medium, with a specified level of assured read performance. This means bits at greater radial displacement from the center of rotation occupy a greater arc length than is needed to be read by the read/write head with the same level of assurance as for the bits adjacent the inner diameter. The extra arc length of all these bits away from the inner diameter reduces the area that can be reclaimed from servo overhead and devoted instead to useful data storage, and so can be considered wasted space, if a way can be found to reclaim this space without degrading other performance aspects. By reclaiming back the servo overhead area, the reclaimed real estate (1) can be used to store more user data and/or (2) enables a reduced data frequency which benefits a lower bit error rate and a better signal to noise ratio (SNR) in reading data. In some illustrative embodiments, the data SNR was improved by 0.4 dB. 
     In some illustrative embodiments, this extra space is reclaimed for user data storage by dividing the medium into separate zones, and writing the servo field bits in a higher frequency for zones away from the inner diameter, such that the farther a zone is from the inner diameter, the higher the frequency is with which the servo field bits are written in that zone. In the specific illustrative embodiments of  FIG. 1 , medium  100  includes the three zones  102 ,  104 ,  106 , and the servo field bits are written in a first frequency in zone  102 , in a second frequency in zone  106  that is higher than the frequency of zone  102 , and a third frequency in zone  104  that is higher than the frequency in zone  102  and lower than the frequency in zone  106 . Zones  102 ,  104 , and  106  may thereby be referred to as differential frequency zones. Because the servo field bits in zones  104  and  106  are written at progressively higher frequencies, they also occupy correspondingly shorter arc lengths than they would have at the single frequency, thereby reducing servo overhead and leaving a greater proportion of the medium available for storing user data. This is demonstrated with the gaps  124  and  126  adjacent to servo fields  114  and  116  respectively. The dotted lines show what the boundaries of these two servo fields would be if the entire medium  100  was written with the frequency with which servo field  112  was written. Gaps  124  and  126  are therefore areas that would have gone to servo field use but instead are freed up for user data storage use, thanks to the use of multiple frequencies in writing the servo bits of medium  100 . 
     As can be seen in  FIG. 1 , each of the servo fields  112 ,  114 ,  116  takes the form of a semi-annular section. Rather than the single semi-annular section for a given servo field that would prevail without dividing the medium  100  into different frequency zones, each servo sector includes a radial row of semi-annular sections constituting separate servo fields, such that the inward semi-annular section  112  has the largest angular spread of servo fields in its servo sector, and each of the other servo fields has an angular spread that is lesser than that of the inwardly adjacent semi-annular section, in some illustrative embodiments. That is, servo field  112  is the inwardly adjacent servo field to servo field  114 , and servo field  114  is inwardly adjacent to servo field  116 . Correspondingly, servo field  114  has a lesser angular spread than servo field  112 , and servo field  116  has a lesser angular spread than servo field  114 . The servo field bits within each of the servo fields  112 ,  114 ,  116  each have an angular spread that is proportional to the angular spread of the servo field within which it is disposed, and an arc length that is the angular spread times the radial displacement from the center of medium  100  at a given position of each respective servo bit, in some illustrative embodiments. Therefore, the servo bits within one of the servo fields have arc lengths that steadily increase proportionately with increasing radius; but going from one servo field to an outwardly adjacent servo field within a servo sector, the arc lengths of the lowest-radius servo bits in the outwardly adjacent servo fields are significantly lesser than the arc lengths of the highest-radius servo bits in the inwardly adjacent servo field. Once again, the arc lengths of these servo bits steadily increases with increasing radius. Thus, the servo field bits in the inwardly adjacent zone have a first range of arc lengths, and the servo field bits in the outwardly adjacent zone have a second range of arc lengths that substantially overlaps the first range of arc lengths. This provides for reduced area devoted to servo function, or servo overhead, for the intermediate and outer zones  104  and  106  relative to inner zone  102 , and relative to what would be required for the entire medium in the absence of differential frequency zoning, for these illustrative embodiments. 
     The following table presents an illustrative example of the servo overhead reduction, comparing a conventional system with a constant servo frequency of 14 MHz and a constant servo overhead of 8.13%, with an example of an illustrative embodiment, using the same specifications as the conventional system for its inner zone: 
     
       
         
           
               
               
               
               
            
               
                   
                   
               
               
                   
                   
                 System According to 
                   
               
               
                   
                 Conventional System 
                 Illustrative Embodiment 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Servo 
                 Servo 
                 Servo 
                 Servo 
                   
               
               
                   
                 Frequency 
                 Overhead 
                 Frequency 
                 Overhead 
                 Reduction 
               
               
                 Zone 
                 (MHz) 
                 (%) 
                 (MHz) 
                 (%) 
                 (%) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Inner 
                 14 
                 8.13 
                 14 
                 8.13 
                 0 
               
               
                 Inter- 
                 14 
                 8.13 
                 17.5 
                 6.52 
                 1.61 
               
               
                 mediate 
               
               
                 Outer 
                 14 
                 8.13 
                 21 
                 5.42 
                 2.71 
               
               
                   
               
            
           
         
       
     
     In the illustrative embodiments, the intermediate zone, corresponding to zone  104 , is written with a frequency of 17.5 MHz, which reduces the size of the servo fields enough to reduce servo overhead to 6.52% in the intermediate zone, so that 1.61% of the medium that would have been devoted to servo bits is instead available for user data storage; and the outer zone, corresponding to zone  106 , is written with a frequency of 21 MHz, which reduces the size of the servo fields enough to reduce servo overhead to 5.42% in the outer zone, so that 2.71% of the outer medium that would have been devoted to servo bits is instead available for user data storage. Because the outer zone contains far more area than the inner zone and more area than the intermediate zone, the overall servo overhead reduction is greater than the figure for the intermediate zone and not much less than that for the outer zone, in this illustrative embodiment. Other embodiments use only two zones, or four or more zones, each with its own servo frequency. 
     In some illustrative embodiments, as the diameter of the medium  100  becomes smaller, the proportion of area reclaimed from servo overhead for user data storage becomes greater. Therefore, this inventive system using differential frequency zones is especially advantageous for very small data storage media and data storage devices, according to these illustrative embodiments. For example, some illustrative embodiments corresponding to the depiction of medium  100  measures approximately one inch across. Other illustrative embodiments corresponding to the depiction of medium  100  occupy a range of diameters less than one inch. Still other illustrative embodiments have larger diameters such as 2.5 inches or 3.5 inches, or other values, while corresponding to scale with medium  100  as depicted in  FIG. 1 . Different embodiments otherwise analogous to medium  100  also include a wide variety of different numbers of zones, and a wide variety of different numbers of servo sectors. 
     One significant issue concomitant with the differential frequency zones, such as zones  102 ,  104 ,  106  in the illustrative embodiments of  FIG. 1 , concerns their characteristics near the boundaries between each adjacent set of zones  102 ,  104 ,  106 . This issue is inventively and advantageously addressed by first guard band  142  and second guard band  144 , disposed between zones  102  and  104 , and between zones  104  and  106 , respectively. The details of such guard bands, in a variety of inventive and advantageous embodiments, are described below, with reference to several of the figures. 
       FIG. 2  depicts data storage system  205  which illustratively embodies the claimed invention, and shows an illustrative context within which the illustrative embodiments of medium  100  may be used.  FIG. 2  depicts an exploded, perspective view of a data storage system  205 , illustratively embodied as a disc drive in these embodiments, which includes medium  100  with optimized servo format, according to illustrative embodiments. 
     Disc drive  205  is one example from a variety of data storage systems to which various embodiments are applicable. Disc drive  205  includes a housing with a deck  212  and a top cover (not shown). Disc drive  205  also includes a disc pack  214  comprising a plurality of mediums  100 . Disc pack  214  is rotatably mounted on a spindle motor (not shown) by a disc clamp  216 . Disc pack  214  includes a plurality of individual mediums  100  which are mounted for co-rotation about central axis  218 . Each medium surface  228  is associated with a slider which is mounted to disc drive  205  and carries a data interface head (“read/write head”)  220 , with read and/or write function for communication with the respective medium  100 , in these illustrative embodiments. 
     In  FIG. 2 , the read/write head  220  is supported by suspension  210  which is rotatably mounted on deck  212 . More particularly, suspension  210  is rotatably mounted on actuator  226 , included on deck  212 , and is thereby disposed on deck  212  in a controllably moveable way. Suspension  210  supplies a pre-load force to the slider which is substantially normal to opposing medium surface  228 . The pre-load force counteracts an aerodynamic lifting force developed between the slider and the medium surface  228  during the rotation of disc pack  214 . Each medium surface  228  is likewise interfaced by a similarly disposed slider (not shown). Actuator  226  is a rotary moving coil actuator and includes a voice coil motor, shown generally at  230 , in these illustrative embodiments. Voice coil motor  230  rotates actuator  226  about pivot shaft  232  to position the read/write head  220  over an intended data track (not shown) along a range  234  between the medium  100  inner diameter  136  and outer diameter  138 . Voice coil motor  230  operates under control of internal circuitry  239 . Other elements may occur in alternative embodiments, such as an actuator that positions the read/write head  220  through linear extension and retraction, for example. 
     The read/write head  220  is thereby configured to be controllably positioned proximate to the medium  100 . The read/write head  220  is capable of reading data from and writing data to the medium  100 , in these illustrative embodiments. The read/write heads  220  may be of any type known in the art, including magnetic, magnetoresistive (MR), giant magnetoresistive (GMR), tunneling giant MR (TGMR), spin valve (SV), optical, and so forth, in various embodiments. In different embodiments, a wide variety of numbers of mediums  100 , with a corresponding number of read/write heads  220  and associated sliders may be used. 
     Medium  100  of disc drive  205  includes radial servo fields disposed at generally regular intervals around the medium  100 , as shown in  FIG. 1 . Likewise, medium  100  is divided into two or more annular zones (not separately shown in  FIG. 2 ), such as the three zones  102 ,  104 ,  106  of  FIG. 1 , each with a respective frequency with which the read/write head  220  is specified to operate within that zone. Each of the servo fields extends across one of the zones. The medium  100  comprises guard bands  142 ,  144  between each pair of adjacent zones, such that the guard bands  142 ,  144  are configured to optimize the capability of the read/write head  220  to remain operating at the respective frequency specified for each zone while the read/write head  220  is in that zone, and to transition to the respective frequency of a new zone from among the zones when the read/write head  220  moves to the new zone. With the servo Fields written at different frequencies in different zones, the read/write heads  220  also use different read frequencies for reading the servo fields in each of the zones. 
     One significant performance issue pertaining to the differential frequency zones is how to transition the read/write head  220  between zones with different servo frequencies, or how to synchronize the servo channel to the servo bursts on different zones with different burst frequencies, particularly when crossing from one of the zones to another. 
       FIG. 3  depicts a relatively simple embodiment of a zone boundary, with only a minimal, single track  335  separating the two zones  311 ,  313  which have different frequencies. The depiction in  FIG. 3  represents a microscopic view of a portion of the medium  100 . Tracks  331 ,  333 ,  335 ,  337  and  339  are portions of concentric tracks that circumscribe medium  100 . The depicted sections of tracks  331 ,  333 ,  335 ,  337  and  339  are actually circle sections, but seen at such close range relative to their diameters they are difficult to distinguish from straight lines. Zone  311  is inward of zone  313 , toward the center of medium  100 ; zone  313  is outward of zone  311 , toward the perimeter of medium  100 . Tracks  331 ,  333 ,  335 ,  337  and  339  are user data tracks, available for writing user data to and reading user data from. Track  335  is depicted as being directly on the boundary between zones  311  and  313 , but is preferably written with one of the adjacent zone frequencies so that user data can be stored there as well. The features depicted in  FIG. 3  are illustrative of features disposed around the wider medium  100 . 
     Servo sectors (which can also be called servo wedges)  321 ,  323 , and  325  lie along radial lines on medium  100 , across the data tracks. Servo sectors  321 ,  323 , and  325  include servo fields. The portions of the tracks within the servo fields contain servo information, such as position and synchronization information, which can be used by the read/write head  220  to control its position relative to representative tracks  331 ,  333 ,  335 ,  337  and  339 , and to sync to the servo fields at the frequency with which they are written. The servo fields in zone  313  are written with a higher frequency than the frequency with which the servo fields in zone  311  are written, in these illustrative embodiments. 
     Read/write head  220  is depicted seeking from track  333  at servo field  321  to track  337  at servo field  323 . However, in this embodiment, it may be difficult for head  220  to perform this seek successfully, and to sync to the servo bursts in zone  313  with the higher frequency of zone  313 . When the head  220  is near the zone boundary at track  335 , it may become likely to experience a missing address mark error, or a loss of synchronization with the new zone servo information before the re-initialization of the servo channel is complete. This would generally require a recovery algorithm to handle, and involves loss of control and predictability. Additionally, in case of a shock to the system while head  220  is near the boundary track  335 , this would also increase the risk of a loss of synchronization with the servo information. 
     A more advantageous embodiment that deals effectively with the preceding performance issues is depicted in  FIG. 4 . This embodiment maintains guaranteed synchronization of the servo channel, predictability of the servo channel performance, and non-interruption of servo tracking and control.  FIG. 4  shows a microscopic view of a portion of the medium  100 . The features depicted in  FIG. 4  are illustrative of features disposed around the wider medium  100 . Tracks  431 ,  433 ,  435 ,  437 ,  439 ,  441 ,  443 ,  445 ,  447 , and  449  are portions of concentric tracks that circumscribe medium  100 , and are circle sections seen at close enough range that they resemble straight lines. Zone  411  is inward of zone  413 , toward the center of medium  100 , while zone  413  is outward of zone  411 , toward the perimeter of medium  100 . 
     This embodiment also includes guard band  415 , which acts as a transition region between zone  411  and zone  413 . Guard band  415  is configured to optimize the capability of the read/write head  220  to remain operating at the respective frequency specified for each of zones  411  and  413  while the read/write head  220  is in each zone, and to transition to the respective frequency of a new zone when the read/write head  220  moves to the new zone, whether one of zones  411  and  413 , or another zone inward of zone  411  or outward of zone  413 , according to different embodiments. This is illustrative of the substantial performance advantages provided by guard band  415 . 
     Tracks on either side of the guard band  415 , including tracks  431  and further tracks in zone  411 , as well as tracks  447 ,  449 , and further tracks in zone  413 , are data tracks available for writing user data to and reading user data from. Servo sectors  421 ,  423 , and  425  lie across the tracks, with the servo fields within one servo sector bordering at a different track within guard band  415  than the next servo sector. For example, as representatively depicted in  FIG. 4 , for servo sector  421 , servo field  451  of zone  411  and servo field  461  of zone  413  border each other at track  443 , close to the border between guard band  415  and zone  413 , so that the servo field  451  from zone  411  extends across most of guard band  415  in servo sector  421 ; for servo sector  423 , servo field  453  of zone  411  and servo field  463  of zone  413  border each other at track  435 , so that servo field  463  from zone  413  extends across most of guard band  415  in servo sector  423 ; and for servo sector  425 , servo field  455  of zone  411  and servo field  465  of zone  413  border each other at track  443 , as in servo sector  421 . In this way, a head  220  following one of the tracks between tracks  435  and track  443  encounters servo fields set at the servo frequencies of both zones  411  and  413 , alternating with each other, as elaborated below. Guard band  415  thereby includes portions of servo fields from each of the two adjacent zones  411  and  413 . This frequency overlap within guard band  415  allows a head to seek there while set to one frequency, and then sync reliably to the new frequency after it is in the guard band. 
     Tracks  433 ,  435 ,  437 ,  439 ,  441 ,  443 , and  445  are included in the guard band  415 . The number of tracks in a guard band, in different embodiments, may range from just one or two to very many, depending on other characteristics and design priorities of the system and other considerations. For example, it depends on reader and writer offset. As another example, it also depends on seek performance criteria such as undershoot, overshoot, resonance response, re-lock performance of the channel, shock performance, and other factors. This is indicated in  FIG. 4  by the break in each of servo sectors  421 ,  423 ,  425 . It is also undesirable for the head  220  to be operating on tracks too near an adjacent zone, because a shock or external vibration may displace the head  220  into the adjacent zone, which could cause loss of servo synchronization, and an operating delay while the head  220  re-obtains sync. In some embodiments similar to that of  FIG. 4 , from five to ten tracks provide an optimum guard band to avoid these performance issues. In another set of embodiments, it has been found advantageous to include about 80 tracks per guard band, as another example. Other embodiments may have more or fewer tracks than these examples. The guard band is designed so that even if the head  220  is operating in a data track closest to the zone boundary, it will not be driven into the adjacent zone by a shock or external vibration, within specified operating tolerances. Another consideration of the number of tracks in the guard band is the user data area loss. If no user data were allowed to be written in a guard band, then too many tracks in a guard band would also result in a lesser area to write user data. 
     Even with the tracks within the guard band being unavailable for writing user data, the gains in efficiency by reducing the circumferential extent of the servo fields provide a substantial overall gain in area available for writing user data. If the medium  100  is divided among too many zones, however, the frequency difference between adjacent zones may become small enough to raise the risk of false address mark (AM) identification. A variety of embodiments are possible that vary the number of frequency zones, the density of servo sectors, and the width of the guard bands to optimize for a variety of specifications and tolerances, and for a variety of applications. 
     While the tracks in the guard bands might not be used to store user data, they can be used to store system data such as drive code, drive parameters, and other drive information and applications, including system data that can be shifted away from the user data tracks, as described in more detail below. This further mitigates the loss of user data capacity involved in areas allocated to the guard bands. 
     Each servo field in zone  411  is disposed along a radial line segment of medium  100 . Although the servo field is “wedge-shaped,” due to being bounded by radial lines at an angle to one another, the servo field can still be described as coinciding with a radial line segment passing through the servo field. The radial line segment can define a unique radial line from the center of medium  100 , passing orthogonally through the inner diameter and the outer diameter of medium  100 , that coincides with and overlaps the radial line segment of a particular servo field. The radial line thus defined by each of the servo fields in zone  411  also coincides with or overlaps a corresponding adjacent servo field in zone  413  that lies in the same one of servo sectors  421 ,  423 ,  425 . The different servo fields within each of servo sectors  421 ,  423 ,  425  thereby line LIP with each other along a common overlapping line, which extends radially through medium  100  in these illustrative embodiments. 
       FIG. 4  depicts the motion of head  220  as it seeks from zone  411  to guard band  415 . Head  220  is depicted initially seeking from track  431  in zone  411  to track  437  in guard band  415 , in an illustrative example of what could be a seek from anywhere in zone  411  to any track in guard band  415 , before moving onward to anywhere in zone  413 . After head  220  has done a seek to track  437  or a comparable track in guard band  415 , head  220  is at first still set to the servo pattern of servo fields  451 ,  455 , and the additional servo fields sharing the servo pattern of zone  411 , which alternate within guard band  415  with the servo fields of zone  413 , including servo field  463 . While on track  437 , head  220  attempts to sync to the new servo pattern of zone  413 , which is available in servo field  463 , for example. As shown in  FIG. 4 , in servo sector  423 , the servo field  463  from zone  413  extends down to track  435 . This allows head  220  to sync to the servo pattern of zone  413  in the guard band  415  at servo sector  423  or, if it doesn&#39;t achieve a sync to the new servo pattern on its first attempt, then at a similar, subsequent servo field extending into the guard band  415  from zone  413 . Many data tracks are available within guard band  415  that intersect the servo fields of both zones  411  and  413 , that provide an optimum chance for head  220  to sync to the frequency of the new zone to which it is seeking. Once head  220  has obtained sync to the new servo pattern, it seeks into zone  413 , as depicted illustratively in  FIG. 4  with a seek from track  437  to track  447  in zone  413 . 
     This process is described here in one particular example that is illustrative of a variety of mechanisms and embodiments. In this particular example, to begin the process of seeking from zone  411  to zone  413 , head  220  first seeks from data track  431  to track  437  within guard band  415 , in servo sector  421 . As head  220  goes from track following mode on track  431 , the channel parameters for the new servo burst frequency are loaded, and a new servo search window for the servo burst of zone  413 , such as is available in servo field  463 , is generated. 
     A seek operation to cross guard band  415  may be illustrated as follows, according to illustrative embodiments. A track-following servo controller (not separately depicted) within internal circuitry  239  (as depicted in  FIG. 2 ), controllably moves the suspension  210  to controllably position read/write head  220  in accordance with the position error signal (PES), to maintain the read/write head  220  centered relative to a given servo track within the servo fields, such as track  437  at servo sector  421 , for example. The servo controller is then switched to half-rate for its passage through guard band  415 , in these illustrative embodiments. The channel searches for the servo address mark of the new frequency of zone  413  with timing to seek to the new zone in servo sector  423 . If head  220  can successfully lock to the new frequency, that of zone  413 , then the servo feedback signal is maintained from the servo burst with the frequency of zone  413 , and the head  220  seeks across guard band  415  to data track  447  in zone  413 , as depicted in these embodiments. 
     If the address mark of the new servo bursts or servo sectors in zone  413  are not found, the old channel parameters for zone  411  are re-loaded, and the servo will search for the servo burst of servo sector  425  with the servo frequency of zone  411  again. Since the track following servo controller is set for half rate, servo sector  425  provides the subsequent PES after servo sector  421 . The head  220  then repeats the process of searching for the new servo address mark of zone  413  until it gets successfully synchronized, in these illustrative embodiments. 
     The embodiments of  FIG. 4  are particularly advantageous for a system in which the time required to switch from the frequency of one zone to the frequency of another zone is longer than half of a normal servo sector time, i.e. the length of time from the head  220  passage over one servo sector to the head  220  passage over the subsequent servo sector, e.g. from the passage over servo sector  421  to servo sector  423 . In some illustrative embodiments, for example, the medium  100  is incorporated in a data storage system such as disc drive  205  that is a fraction of one inch across, and the servo sector time is in the neighborhood of 100 microseconds. Embodiments such as those illustratively depicted in  FIG. 4  may be of particular benefit for such a small disc drive, since it may also have a lower servo burst frequency than a larger disc drive. For example, one illustrative sub one inch disc drive uses a servo burst frequency of 15 MHz (at a rotational speed of 3600 rpm), while a representative larger size 3.5 inch drive uses a servo burst frequency of 60 MHz (at a rotational speed of 5400 rpm). Because the smaller drive has a lower servo frequency, it also has lower format efficiency, and all the more to gain by improving on that efficiency by implementing an optimized servo format such as the embodiments disclosed herein. 
     The strategy of loading read channel servo parameters for different sets of servo burst frequencies in the guard band  415 , in illustrative embodiments, is to maintain operational condition for both the sets. This is achieved by saving a copy of critical read channel servo parameters (copy X) such as the frequency registers, programmable filters and adaptive filters values upon the exit of a current servo frame/burst (frequency X) and loading read channel servo parameters for the next servo frame/burst which is at the new frequency (frequency Y). Again, upon the exit of the new servo frame/burst with frequency Y, a copy of the read channel servo parameters (copy Y) is saved by the controller. Copy X is then loaded in preparation for entry into the servo frame with frequency Y. This process is repeated until the servo frame/burst with frequency Y of the next zone is locked on and the head  220  moves out of guard band  415 . The time required to load new parameters for a new servo burst frequency is in the range of 10 microseconds or less, in some illustrative embodiments. This allows plenty of time for the channel to load the parameters for one or another zone&#39;s frequency between one servo sector and the next. 
       FIG. 5  depicts other illustrative embodiments that are similar to the embodiments of  FIG. 4 , and are particularly advantageous for a system in which the time required to switch from the frequency of one zone to the frequency of another zone is within half of a normal servo sector period. In writing the servo pattern, if the writing head  220  is able to switch servo burst frequency within a half sector, then one-pass write can be used, as in  FIG. 5 . Otherwise, the servo bursts in the transition zones can be written in two-pass, as in  FIG. 4 . In some illustrative embodiments, for example, the medium  100  is incorporated in a data storage system such as disc drive  205  that is a fraction of one inch across with a servo sector time somewhere of 100 microseconds, while the system can switch from the frequency of one zone to the frequency of another zone in around 40 microseconds or less. To take advantage of this, the zone  513  servo burst timing positions are shifted by half of a servo sector from the servo fields of zone  511 . 
     The illustrative embodiments of  FIG. 5  is another example that maintains guaranteed synchronization of the servo channel, predictability of the servo channel performance, and non-interruption of servo tracking and control.  FIG. 5  shows a microscopic view of a portion of a medium  100 , in which tracks  531 ,  533 ,  535 ,  537 ,  539 ,  541 ,  543 ,  545 ,  547 , and  549  are portions of concentric tracks that circumscribe medium  100 , and are circle sections seen at close enough range that they resemble straight lines. Zone  511  is inward of zone  513 , toward the center of medium  100 , while zone  513  is outward of zone  511 , toward the perimeter of medium  100 . These illustrative embodiments also include guard band  515 , which acts as a transition region between zone  511  and zone  513 . Tracks  533 ,  535 ,  537 ,  539 ,  541 ,  543 , and  545  are included in the guard band  515 . Tracks on either side of the guard band  515 , including tracks  531  and further tracks in zone  511 , as well as tracks  547 ,  549 , and further tracks in zone  513 , are user data tracks available for writing user data to and reading user data from. The features depicted in  FIG. 5  are illustrative of features disposed around the wider medium  100 . 
     Servo sectors  521  and  523  lie across the tracks, and each includes one servo field from zone  511  and one servo field from zone  513 . Servo sector  521  includes servo field  561  from zone  511  and servo field  563  from zone  513 , while servo sector  523  includes servo field  565  from zone  511  and servo field  567  from zone  513 . (Servo field  569  forms a portion of another servo sector, not individually labeled.) Servo sectors  521  and  523  differ from those in  FIG. 4  in that each of the servo sectors  521 ,  523  comprises servo fields that are angularly offset from each other, so that the servo fields within a single servo sector overlap some of the same tracks within guard band  515 , for example. In particular, servo fields  561 ,  565  and  569  are in the inner zone  511 , while servo fields  563  and  567  are in the outer zone  513 . 
     Read/write head  220  is depicted in  FIG. 5  to have an initial position in zone  511  (as an example, on track  531 ), at servo field  561  in servo sector  521 , and is preparing to seek to zone  513 , as an illustrative example of operation with medium  100 . Head  220  first seeks to guard band  515 ; specifically, for example, to track  537 , also on servo field  561 , which extends across guard band  515 . Once head  220  has entered guard band  515 , the channel parameters for the new servo burst frequency are loaded and a new servo search window for the servo burst of servo field  563  are generated. The channel will search for the servo address mark in servo field  563  of the new frequency of zone  513  at a half sector time away from servo field  561 . If the channel can successfully lock to the address mark at the new frequency of zone  513 , then the servo feedback signal switches to the servo burst with the new frequency of zone  513 . Otherwise, the old channel parameters for zone  511  are reloaded, and the channel will search for the servo burst with the servo frequency of zone  511  again. Then, the head  220  will repeat the process of searching for the new servo address mark of zone  513  until it successfully gets synchronized. 
       FIG. 6  depicts another illustrative embodiment, this one including transitional servo field segments  651 ,  653  within an adjacent pair of guard bands  615 ,  617 . Guard bands  615 ,  617  may contain any of a wide number of tracks, as indicated by the breaks depicted in the servo fields in both guard bands  615 ,  617 . These embodiments also have servo fields in adjacent zones lined up in the same radial servo sectors, doing without a servo sector period shift from zone to zone as in the embodiments of  FIG. 5 . Medium  100  includes two guard bands  615 ,  617 , disposed side by side between inward zone  611  and outward zone  613 . In guard band  615 , servo frequency switching is accomplished as described above. In guard band  617 , head  220  re-locks to the servo bursts of zone  613  on a servo field coinciding along a radial line with the servo field it started seeking through the guard bands from, in servo sector  621 . Medium  100  therefore includes some transitional servo field segments  651 ,  653  that are offset from the radial lines coincident to the servo fields in both the inner zone  611  and in the outer zone  613 . Transitional servo field segments  651 ,  653  are angularly separated from the servo fields in the first zone  611  and from the servo fields in the second zone  613 . 
       FIG. 7  depicts other illustrative embodiments, also with two guard bands  715 ,  717  between adjacent zones  711 ,  713 , and also without a servo sector timing shift. These illustrative embodiments also lack an overlap in servo fields on any data tracks. Medium  100  includes two guard bands  715 ,  717 , disposed side by side between inward zone  711  and outward zone  713 . In guard band  715 , when the predicted position of head  220  in the subsequent servo sector (such as sector  723 ) is in second guard band  717 , servo frequency switching is accomplished as described above. Head  220  then seeks from servo sector  721  in guard band  715  to servo sector  723  in guard band  717 . If head  220  is able to sync successfully with the frequency of outward zone  713 , it passes out of second guard zone  717  into outward zone  713 ; otherwise it repeats the attempt to sync in the next servo sector. Guard bands  715  and  717  provide further assurance of the reliable performance of head  220  in each of representative zones  711  and  713 . 
     In any of the above or further embodiments, the depicted elements are representative of any number of zones, guard bands, servo sectors, and other elements that can be selected in different embodiments. For example, a medium  100  may have zones determined by dividing equal portions of the radius of the medium  100 ; in other embodiments, it is more efficient to use uneven spacing for the boundaries between zones, such as by increasing the radial width of the outer and/or outward zones, which have tracks of greater arc length, and a lowered radial width of the inner and/or inward zones. Tracks closer to the outer diameter are capable of holding more data, so if servo zones closer to the outer diameter have more tracks, it can further improve the format efficiency. 
     As another example, the fast sync-up time is a significant factor in determining optimum relative zone sizes. In some disc drives of one inch or less in diameter, for example, the ramp load/unload technique may be used. The load/unload ramp may be located on either the inner diameter or the outer diameter of the medium  100 , in various embodiments. When the initial sync-up is done in the inner zone, the head can be tuned to the inner zone servo burst frequency. During the address mark (AM) locking period, the head can shuttle in the inner zone under a back electromotive force (BEMF) speed/position control feedback signal. Since the inner zone crash stop location can be easily determined, the stroke of the shuttle action can be easily confined to the inner zone. In case of a retry from a missing AM, the head can switch to the servo burst frequency of the inner zone and move back to the inner zone to re-sync up. 
     Initial loading in the outer zone is also based on a BEMF feedback signal, in some embodiments. Experimentation on some illustrative embodiments with a ramp at the outer diameter, in various operating conditions, has shown that the first sync up location is often in the middle of the outer zone of the medium  100 , adjacent the outer diameter. This first sync-up can use feedback from a gray code in the servo fields, for example. After sync-up and good gray code is available from time to time, the feedback signal for head velocity control can be switched from BEMF to gray code. As the velocity loop in sync-up process has a relatively low bandwidth, the good gray code feedback signal can be much less frequent than PES in track following control. 
     To achieve a fast sync-up, an embodiment having a relatively larger outer zone may be advantageous in providing certainty that the initial sync-up will take place there, rather than allowing a significant risk of the read/write head moving to the next inward zone prematurely and losing sync. Preventing the head from moving prematurely past the outer zone is also easier with the head velocity relatively low, for example, less than one inch per second, in illustrative embodiments. After the first sync-up in the outer zone, the velocity reference may be reduced to zero, in these embodiments, to further prevent the head from crossing the zone boundary prematurely. With the head position estimated with reference to the BEMF feedback signal, if the estimated head position is too close to the zone boundary, the velocity reference may be changed to the opposite direction. Another method of assuring sync-up is to toggle between the servo frequencies of the outer zone and the next inward zone until the head successfully locks up to the servo bursts of its position. 
     The seeking operations within a given servo zone are similar to those in conventional data storage systems, in illustrative embodiments. When seeking across servo zones, the frequency in the servo fields change. The servo channel needs to change accordingly to sync to the new frequency. A track position prediction of the next servo sector, and evaluating whether it belongs to another zone, are important for preparing the channel for the new zone. For state feedback control, the track prediction can be done directly from the position variable in the state estimator. 
     Generally, with X as the head position, V as the head velocity, and A as the head acceleration, the track prediction can be derived by
 
 X ( k+ 1)= X ( k )+ V ( k )+0.5 *A ( k )
 
 V ( k )= V ( k− 1)+ A ( k− 1)
 
 X ( k )= X ( k− 1)+ V ( k− 1)+0.5 *A ( k− 1)
 
     These can be used to derive the following relations:
 
 V ( k− 1)= X ( k )− X ( k− 1)−0.5 *A ( k− 1)
 
 V ( k )= X ( k )− X ( k− 1)+0.5 *A ( k− 1)
 
 X ( k+ 1)= X ( k )+ X ( k ) −X ( K− 1)+0.5 *A ( k− 1)+0.5* A ( k )
 
     The track prediction by the last of these relations is accurate enough for prediction of the zone of the next servo sector. If a more accurate prediction is desired, a relation can be used which further includes corrections for code delay. This is illustrative of one possible example among many servo algorithms that may be used to perform track prediction. 
     If the estimated track of the next servo sector will be in the next frequency zone, the channel loads the parameters for the next frequency zone at the boundary track. With a parallel interface channel, the time for switching between two sets of parameters for two adjacent zones is within 20 microseconds, in illustrative embodiments. The servo synthesizer settling time can be controlled to less than 30 microseconds, in these embodiments. For a sub-one-inch disc drive with limited servo sampling frequency, there is enough time for frequency switching before a subsequent servo frame with a different frequency. In embodiments in which the servo channel has pre-stored banks of servo channel data, the switch to the new frequency is even faster. 
     Servo fields may be written in different ways, including in-situ and ex-situ. For in-situ written systems with more than one head (such as STW, self-servo), the current head and the head to be switched to will be on the same track and the same zone from one medium  100  to another. Head switching then correlates for each of the heads across the mediums  100 . However, head switching is a little more complicated in embodiments that have had the servo fields written ex-situ. 
     For ex-situ written systems, there may be a variation or skew in the alignment, between the different heads and corresponding mediums  100  within the system. For example, this skew was found to be as much as 800 tracks in illustrative embodiments in which each medium  100  had a track density of 100,000 tracks per inch. Because of this skew, one head may be in one zone while other heads are in adjacent zones on their corresponding mediums  100 . The position of a head to be switched to, i.e. a target head, is needed for setting the proper zone parameters for the servo channel during the head switch. The head alignment offset between heads follows a curve having a sine waveform with some DC component. The head alignment offset between the heads in some embodiments has been calibrated in a certification test to evaluate the head alignment offset, including DC offset, AC peak, and AC peak location, for each zone boundary, including the outer diameter, the intermediate diameter zone boundaries, and the inner diameter. With the calibration data and the prediction of the current head position at the next servo sector, the target head position at the next sector can also be computed. The computed position of the target head is used to avoid switching the head position to an unusable track between zones and the resulting missed sync-up. The computed position of the target head at the next servo sector is evaluated prior to a head switch. If it is outside of an unsafe head switch position, the decision to switch to the target head can be made. Whether the target head position is in a new frequency zone is also evaluated, and a frequency switch is also performed if needed. The algorithm used therefore insures that the heads will be kept in safe tracks where they will remain in sync, despite any head skew. This demonstrates illustrative embodiments of a means for controllably positioning the read/write head from a first one of the zones to a second of the zones, and a means for changing the operating frequency of the read/write head from the respective frequency of the first one of the zones to the respective frequency of the second one of the zones, included within illustrative embodiments of a data storage system. 
     If the head does lose sync, there are a number of techniques that may help it regain sync with the servo tracks, any or all of which may be applicable to given embodiments. Re-sync can be done in a zone with zero bias force position. When servo sync is lost, the head can be switched to zero velocity control based on BEMF and then left to drift to a zero force bias position. Then the channel parameters for that zone are set, and re-lock is attempted. If this fails, the head can be unloaded to restart sync-up with the head being re-loaded. 
     As another technique, when sync is being lost, the servo switches to BEMF control. Based on the last track number, velocity, and acceleration information before losing sync, and integration of the BEMF, the head can be approximately controlled into a selected zone. The head shuffles in this zone and tries to re-lock. If this attempt times out, the head is unloaded and sync-up is restarted from head loading. Whatever re-sync technique is used, the demodulation sync process should ensure a sufficient track clearance from a zone boundary before turning control over to a recovery seek process, to make sure the actuator builds up enough velocity for crossing the zone boundary. 
     The embodiments described so far have dealt generally with a guard band of tracks medially disposed between and contiguous to a first band of consecutive user data storage tracks servo formatted with a first frequency and a second band of consecutive user data storage tracks servo formatted with a second frequency different than the first frequency. The guard band is provided as a place not to store and retrieve user data in the normal course of processing access commands, but rather as a frequency shift “safe harbor” where the head can sync to a different frequency before entering the zone associated with the new frequency. 
     However, frequency shifting is not the only purpose for which guard bands of storage tracks are used between and contiguous to two zones of user data storage tracks.  FIG. 8  depicts the head  220  having separate write (W) and read (R) elements  802 ,  804 , respectively. The write element  802  is preferably an inductive horizontal or vertical writer, and as described above the read element can be of any desired construction such as but not limited to MR, GMR, TGMR, and SV. 
     As depicted, the effective radial width of the write element  802  is greater than that of the read element  804 . This means that only a portion of the radial width of a written track is necessary for reading stored data from the track. To store data to the medium  100  in the arrangement depicted in  FIG. 8 , the head  220  can be initially positioned so as to place the write element  802  in a substantially centered relationship over track centerline  806 . The head  220  then tracks at that radial position while storing data to a first track  808  (Track  0 ). As depicted, data stored in the first track  808  will initially have a radial width substantially equivalent to that of the effective width of the write element  802 . 
     On a subsequent pass (another rotation) of the medium  100 , the head  220  seeks to substantially center the write element  802  over the adjacent track centerline  810 . The head  220  then tracks at that radial position while storing data to a second track  812  (Track  1 ). The second track  812  partially overlaps the first track  808 , and thereby partially overwrites it, but the first track  808  retains a sufficient radial width to permit the read element  804  to read the data stored to it. 
     Any number of additional overlapping tracks can be written in this manner. For example, by tracking on centerline  814  a third track  816  (Track  2 ) can be written that partially overlaps the second track  812 ; by tracking on centerline  818  a fourth track  820  (Track  3 ) can be written that partially overlaps the third track  816 ; and so on. 
     This partial overlapping of tracks increases the track density on the medium  100 , and can thereby significantly increase the total storage capacity of the medium  100 . The limiting factor for track density becomes a factor of the read element  804  instead of the write element  802 . 
     However, the use of overlapping tracks raises issues regarding the operational overhead that is required to update data that was previously stored in an overlapped track. For example, in order to update the data on the second track  812 , merely aligning the write element  802  with centerline  810  and performing a new write operation to the second track  812  will also result in the undesired overwriting of the data stored to the third track  816 . Thus, in order to update data stored to the second track  812  without losing the data stored to the third track  816  it is necessary to first read and temporarily buffer the data stored to the third track  816  and stored to the fourth track  820 , update the data to the second track  812 , and then rewrite the buffered data to the third track  816  and to the fourth track  820 . 
     Thus, the overlapping track arrangement of  FIG. 8  is well suited for data that is characterized as seldom being updated. Otherwise, updating data stored to an overlapped track requires first buffering and then restoring all data in downstream overlapping tracks. For purposes of this description “downstream” is a relative term with respect to the radial direction with which the next overlapping track is written. That is, the overlapping can be performed either inwardly or outwardly across the medium  100 . 
     Preferably, one or more non-overlapping tracks such as the fifth track  822  is periodically formatted with its centerline  824  being disposed a full write element  802  width from the adjacent centerline  818 . The non-overlapping track or tracks serve as a guard band ceasing the cascading effect of the overlapping tracks. That is, the data stored to the fourth track  820  can be updated without overwriting data previously stored to the fifth track  822 . 
       FIG. 9  diagrammatically depicts a manner in which a plurality of these bands of overlapping tracks can be arranged on the medium  100  in accordance with advantageous embodiments to increase the storage capacity of the medium  100 . A plurality of bands  902  includes a first band  902   1  of consecutive overlapping user data storage tracks and a second band  902   2  of consecutive overlapping user data storage tracks, with an annular guard band  904   1  medially disposed therebetween and contiguous to both bands of user data storage tracks  902   1 ,  902   2 . 
     Two different purposes have been described for allocating some tracks as guard tracks medially disposed between two bands of contiguous user data tracks, the purpose of facilitating smooth frequency shifting between bands and the purpose of separating bands of overlapping tracks. These purposes are illustrative and not limiting of all the purposes for which guard tracks might advantageously be formatted in the medium  100 . In any event, however, setting tracks aside for use as guard tracks typically makes it disadvantageous to store user data in them. For example, an attempt at storing and retrieving user data to guard tracks separating different frequency zones in the normal course of data transfer operations would diminish the intended benefit of having the guard tracks for the purpose of smoothly shifting frequencies between the adjacent zones. That is, such an arrangement would often require the overhead resources and time penalty associated with obtaining sync to a different frequency, at half the normal sample rate, for retrieving the limited amount of user data that can be stored in the relatively few tracks allocated to be guard tracks. Also, in either of the examples set forth above, storing user data in the guard tracks will tend to disperse the user data that could more efficiently be stored in contiguous tracks, thereby increasing the seek time for retrieving the user data. 
     Nonetheless, not using the guard tracks for storing anything but servo sectors means paying the penalty of less than the optimal utilization of the medium  100  total storage capacity. The guard tracks described herein are well suited for storing information that is stored once and seldom retrieved. The present embodiments take advantage of that by storing system sectors to the guard tracks. That frees up the storage space that the system sectors would otherwise be stored to, thereby recovering valuable user data storage space that would otherwise be lost due to the system sectors being stored elsewhere than the guard tracks. 
     System sectors have certain system data stored therein concerning the configuration and operation of the data storage device. For purposes of this description and the appended claims, “system data” means non-servo configuration and operation data such as information concerning zone configurations, frequencies with which data is stored in the various zones, reassignment tables that associate virtual addresses to physical addresses on the medium  100 , sector defect lists, and the like. The system data is used by a device controller in the data storage device to control its operation during the normal course of user data transfer operations. Typically, at power-on and reset conditions the system data is read once to the device controller to govern the storage device operation. 
     At power-on a computing device initially executes a boot sequence that informs the operating system of the location of a minimum number of files necessary to obtain operational control and carry on with the boot sequence to achieve a ready/standby state. Those initial files are sometimes referred to as boot sectors, which can be stored in the locations described herein as being allocated for system sectors. For example, executing the boot sectors can result in first loading a reserve sectors map (RSM) that informs the operating system as to the location of all the files, or system sectors, in a reserved zone. 
       FIG. 10  is a diagrammatic depiction of a sector of the storage medium  100 , showing portions of its inner and outer edges  136 ,  138  adjacent its innermost and outermost user data storage tracks  137 ,  139 . Six bands of consecutive user data storage tracks are separated by five respective guard bands of one or more tracks. The bands of consecutive user data storage tracks can have data stored thereto with different frequencies, or they may be bands of overlapping tracks, or they may be zoned for another reason. In any event, the system sectors might be entirely stored in Guard Band A. Clearly, by being “entirely” in Guard Band A can include other system sectors in the same tracks as in Guard Band A and other sectors of the medium  100 . However, if more storage capacity is needed for the system sectors, then a first portion of the system sectors can be stored in Guard Band A and a second portion of the system sectors can be stored in Guard Band B. In that case, loading the RSM can result in the system mapping all the locations of the system sectors in both guard bands. Alternatively, loading the RSM can result in the system only mapping the locations of the system sectors in Guard Band A. The system sectors in Guard Band A can include executable instructions that map the additional system sectors in Guard Band B. 
     Generally, the system sectors contain system data. For purposes of this description and meaning of the appended claims, the term “system data” is generally distinguished from “user data” in that the system data is information used by the data storage device in controlling its operations in the normal course of data transfer steps. User data is the object of host access commands that store data to and retrieve data from the user data zones that do not include the guard bands where the system sectors reside. 
       FIG. 11  is a diagrammatic depiction of the track  437  to which the head  220  is initially tracking in  FIG. 4 . While the servo format arrangement of  FIG. 4  associated with zoned user data tracks for frequency shifting is referred to, the purpose for doing so is merely illustrative and not limiting of the claimed embodiments. That is, the following discussion is also applicable to zones of overlapping user data tracks or zone formatted user data tracks generally. 
     Each of the servo fields  421 ,  423 ,  425  include an automatic gain field (AGC)  902 , a synchronization field (SYNC)  904 , an index field (INDEX)  906 , a Gray code field (GC)  908 , and a position field (POSITION)  910 . The AGC  902  stores an oscillating pattern (such as a 2T pattern) used to prepare the servo circuitry for remaining portions of the servo field  423 . The SYNC  904  stores a unique bit pattern that identifies the field as a servo field. The INDEX  906  indicates angular position of the head  220  with respect to the medium  100 . The GC  908  stores track address information to indicate radial position of the head  220 . The POSITION  910  has dibit burst patterns to allow generation of a position error signal to identify inter-track head  220  location. 
     Between adjacent servo fields  423 ,  425  system sectors  912   1 ,  912   2 ,  912   3  are formatted to the medium  100 . The three such system sectors is illustrative and not in any way limiting of the contemplated embodiments, as the size and number of system sectors  912  between adjacent servo fields is dependent upon the servo sampling rate and the allocated storage capacity for each system sector  912 . 
     Encoded system data blocks are stored in the data field (SYSTEM DATA)  924 . Such data blocks are generally composed of a fixed-size block of data and an associated number of error correction code (ECC) bytes. The size of the system data blocks will generally be established by the host device operating system at the time of formatting; typical values are 512 bytes, 1024 bytes, 4096 bytes, etc. 
     Summarizing,  FIG. 4  depicts the storage medium  100  as having a guard band  415  having a plurality of guard tracks  433 - 445 . Note that in these illustrative embodiments there are a plurality of guard tracks in the guard band  415 . Preferably, the innermost guard track  433  is consecutive with the outermost user data storage track  431  in the band  411 , and outermost guard track  445  is consecutive with the innermost user data storage track  447  in the band  413 . 
     One or more of the guard tracks, such as guard track  437 , define system sector fields of system sectors  912  stored thereto between adjacent servo fields  421 ,  423 ,  425 . The data storage tracks in the band  411  define user data fields of user data sectors  470  stored thereto also between adjacent servo fields  421 ,  423 ,  425 . Likewise, the data storage tracks in the band  413  define user data fields of user data sectors  472  stored thereto also between adjacent servo fields  421 ,  423 ,  425 . The user data sectors  470 ,  472  in the same sector of the medium  100 , such as between servo fields  421  and  423 , and the system sectors  912  in the guard tracks  433 - 445  can form a continuous non-servo data field extending radially from an innermost data storage track of the first band  411  to an outermost data storage track of the second band  413 . In the bands  411  and  413  this non-servo data field contains user data sectors, and in the guard band  415  this non-servo data field contains system sectors. 
     With reference to  FIG. 10 , the format described above can be carried across two or more guard bands where the storage capacity of one guard band is insufficient to store all the system sectors. The system sectors can be stored in two or more guard bands adjacent consecutive bands of user data storage tracks, such as in Guard Track A and Guard Track B. Alternatively, the system sectors can be stored in two or more guard bands adjacent non-consecutive bands of user data storage tracks, such as in Guard Track A and Guard Track E. In any event, in some embodiments a system sector in one of the guard bands includes executable instructions that inform the operating system of the whereabouts of the system sectors in the other guard band. 
     Ultimately, illustrative embodiments contemplate a data storage device such as but not limited to device  205  in  FIG. 2  that has a storage medium  100  containing a plurality of different storage locations for storing user data. The storage locations include a minimum designated storage location, such as the innermost user data storage track  137  ( FIG. 1 ), the least LBA, or the like. The storage locations likewise include a maximum storage location, such as the outermost user data storage track  139 , the greatest LBA, or the like. The minimum and maximum storage locations define the extremities of a user data storage space continuum on the storage medium. 
     The claimed embodiments further contemplate a means for optimizing a utilization of the storage medium  100  by storing system sectors  912  to storage locations within the user data storage space continuum. For purposes of this description and meaning of the appended claims, “means for optimizing” includes the structure disclosed herein and the structural equivalents thereof that permit the storage and retrieval of system sectors within data storage tracks that are bounded on both sides by user data storage tracks. “Means for optimizing” expressly does not include prior attempted solutions whereby the system sectors are otherwise stored in tracks outside the extremities of the user data storage space continuum, such as in a band of tracks at an innermost diameter or an outermost diameter of the medium  100  that are reserved for system sectors and not utilized for storing user data. 
       FIG. 10  is a flowchart depicting steps in a method  1000  for a power-on-reset routine in accordance with embodiments of the claimed invention. The method  11000  can be implemented by the data storage device  205  executing a series of programming instructions stored in memory. 
     The method  1000  begins with load operation  1002  in which the RSM is loaded. Again, the RSM is a table or map that informs the operating system as to the location of all the files in a reserved zone. Control then passes to block  1004  in which the system sectors  912  are loaded. Again, the system sectors  912  contain the information that is necessary to the device controller in order to process data access commands in the normal course of transactions. The system sectors  912  can contain information such as channel parameters, zone boundaries and associated zone information such as frequency with which the data is stored, drive configurations, register values, and the like. 
     After the system sectors are loaded, a number of additional load operations can take place. For example, in load operation  1006  a defect table is loaded. The defect table defines the locations of defects in the medium  100  that were identified during certification testing of the medium  100 . The defect table is system data that is well suited for being stored in the system sectors  912 . 
     In load operation  1008  a defect logical zone table is loaded. The defect logical zone table is basically a conversion of the defect locations from a cylinder-head-sector (CHS) format into logical block addressing (LBA) format. The defect logical zone table is system data that is also well suited for being stored in the system sectors  912 . 
     In block  1010  the main overlays are loaded. The entire firmware includes several overlays (or files), the main overlay containing all the codes that are fundamentally important to drive functionality. Finally, in block  1012  RAM code is loaded which completes the code necessary for functionality but not included in the main overlays. The data storage device thus stands ready to process data access commands with a host device. 
     The present embodiments therefore include unexpected and novel advantages as detailed herein and as can be further appreciated from the claims, figures, and description by those skilled in the art. Although some of the embodiments are described in reference to a data storage medium or a data storage system, or to even more particular embodiments such as a disc or a disc drive, the claimed invention has various other embodiments with application to other data storage technologies. 
     It is to be understood that even though numerous characteristics and advantages of various illustrative embodiments of the invention have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present embodiments, to the full extent indicated by the broad, general meaning of the terms in which the appended claims are expressed. It will be appreciated by those skilled in the art that the teachings of the present embodiments can be applied to a family of systems, devices, and means encompassed by and equivalent to the examples of embodiments described, without departing from the scope and spirit of the claimed embodiments. Further, still other applications for various embodiments, including embodiments pertaining to data storage media and data storage systems, are comprised within the claimed embodiments.