Abstract:
Disclosed herein are methods and apparatuses that provide for variable data density on a disc data storage medium, where the variable data density may have a circumferential definition and a radial definition. In some examples, devices and methods may include measuring a read or write performance attribute on a disc data storage medium and selectively setting a data density rate that may vary in a circumferential direction for the disc data storage medium based on the read or write performance attribute. In other examples, apparatuses can include a data storage device having a disc data storage medium and a controller configured to measure a performance attribute of the disc data storage medium and to selectively set different Bits Per Inch (BPI) for data storage within different areas of the disc.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2011-0062709, filed on Jun. 28, 2011, the entire disclosure of which is hereby incorporated by reference. 
       BACKGROUND 
       [0002]    Embodiments of the present disclosure relate to a Bits Per Inch (BPI) control method for a disk and a hard disk drive (HDD) controlled by the same, and particularly, to a BPI control method for a disk capable of increasing a capacity and enhancing reliability by differently controlling BPI of a disk in a circumferential direction, and an HDD controlled by the same. 
         [0003]    A hard disk drive (HDD), one of data storage devices contributes to an operation of a computer system by reading data recorded onto a disk or by recording user data onto a disk by a magnetic head. 
         [0004]    Due to recent trends of the HDD, such as a high capacity, high density and miniaturization, a more sophisticated mechanism is required. 
         [0005]    A recording medium of the HDD, a disk has a magnetic recording layer recorded on its surface by a thin film application method. Here, an expected capacity may become deficient and reliability may be degraded due to micro non-uniformity occurring on the disk surface. The non-uniformity may mean a physical/chemical flat degree of the disk surface. 
         [0006]      FIG. 1  illustrates a BPI control graph with respect to a disk in accordance with the conventional art, and  FIG. 2  is a graph schematically illustrating a correlation between a disk and BPI. 
         [0007]    Referring to  FIG. 1 , BPI of an HDD being presented to the market is differently controlled with consideration of an angular speed in a radial direction (a). That is, the HDD is controlled so that its BPI can increase towards an outer radius (OR) longer than an inner radius (IR). 
         [0008]    In the conventional art, the HDD is controlled to have the same BPI since BPI control in a circumferential direction (b), a cylinder direction of the disk is complicated or difficult. As a result, an expected capacity may become deficient and reliability may be degraded due to micro non-uniformity occurring on the disk surface. 
         [0009]    Referring to  FIG. 2 , the disk surface onto which a magnetic recording layer is recorded by a thin film application method cannot have an ideal complete planar surface. According to a flat degree, the disk surface may have a position (D 1 ) of high read/write performance, and a position (D 2 ) of low read/write performance. That is, the disk has a non-uniform surface (P) relatively lower than the other surface. 
         [0010]    Such phenomenon always occurs while manufacturing a disk. As shown in  FIG. 2 , if the HDD is controlled to have the same BPI in a circumferential direction (b) without consideration of such phenomenon, an expected capacity may become deficient and reliability may be degraded due to the non-uniform surface (P). 
         [0011]    To solve such problems, BPI may be decreased, which results in a large size of data. If a data size increases, an error rate during a read operation is reduced, but a capacity is lowered. 
         [0012]    On the contrary, if BPI is increased, a data size decreases thus to increase a capacity. However, in this case, an error rate during a read operation increases. 
         [0013]      FIG. 3  is a graph illustrating Over Write (OW) on the disk surface in a circumferential direction (Media OW), and a read/write error rate on a corresponding position. 
         [0014]    Referring to  FIG. 3 , the OW on the disk surface, and a bit error rate (BER) on a corresponding position change in proportion to each other. 
         [0015]    Such phenomenon may occur due to a non-uniform degree on the disk surface. This may cause degraded reliability that a reading or writing operation cannot be successfully performed on a position having low OW. 
         [0016]    In order to solve such degraded reliability, the entire BPI applied to the HDD may be lowered, or the OW on the disk surface may be increased. In this case, the HDD may have a decreased capacity, and may have degraded productivity due to a reduced yield. 
         [0017]    As aforementioned, the HDD has different read/write performance due to non-uniformity on the disk surface. However, if the HDD is controlled to have the same BPI on the surface in a circumferential direction like in the conventional art, a capacity may become deficient and reliability may be degraded. Therefore, a new solution is absolutely required. 
       SUMMARY 
       [0018]    Disclosed herein are methods and apparatuses that provide for variable data density on a disc data storage medium, where the variable data density may have a circumferential definition and a radial definition. In some examples, apparatuses and methods may include measuring a read or write performance attribute on a disc data storage medium and selectively setting a data density rate that may vary in a circumferential direction for the disc data storage medium based on the read or write performance attribute. In other examples, apparatuses can include a data storage device having a disc data storage medium and a controller configured to measure a performance attribute of the disc data storage medium and to selectively set different Bits Per Inch (BPI) for data storage within different areas of the disc. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments and together with the description serve to explain the principles of the invention. 
           [0020]    In the drawings: 
           [0021]      FIG. 1  is a BPI control graph with respect to a disk in accordance with the conventional art; 
           [0022]      FIG. 2  is a graph schematically illustrating a correlation between a disk and BPI; 
           [0023]      FIG. 3  is a graph illustrating Over Write (OW) on a disk surface in a circumferential direction, and a read/write error rate on a corresponding position; 
           [0024]      FIG. 4  is a partial disassembled perspective view of an HDD to which a BPI control method for a disk according to a first embodiment; 
           [0025]      FIG. 5  is a schematic planar view of a disk region; 
           [0026]      FIG. 6  is a view illustrating a data format of each track; 
           [0027]      FIG. 7  is a view illustrating a detailed configuration of a servo sector; 
           [0028]      FIG. 8  is a schematic control block diagram of the HDD shown in  FIG. 4 ; 
           [0029]      FIG. 9  is a flowchart illustrating a BPI control method for a disk in a circumferential direction; 
           [0030]      FIG. 10  is a flowchart illustrating a BPI control method for a disk in a circumferential direction according to a second embodiment; 
           [0031]      FIG. 11  is a schematic planar view of a disk region to which the control method of  FIG. 10  is applied; and 
           [0032]      FIG. 12  is a schematic planar view of a disk region to which a BPI control method for a disk according to a third embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    Description will now be given in detail of the exemplary embodiments, with reference to the accompanying drawings. For the sake of brevity with reference to the drawings, the same or equivalent components will be provided with the same reference numbers, and a detailed description thereof will not be repeated. 
         [0034]    An aspect of the embodiments described herein is to provide a BPI control method for a disk capable of increasing a capacity and enhancing reliability by differently controlling Bits Per Inch (BPI) of a disk in a circumferential direction, and an HDD controlled by the same. The embodiments disclosed herein are capable of increasing a capacity and enhancing reliability by differently controlling BPI of a disk in a circumferential direction, based on a read/write performance difference due to non-uniformity on the disk surface. 
         [0035]    To achieve these and other advantages as embodied and broadly described herein, there is provided a BPI control method for a disk, the method comprising: (a) measuring read/write performance on a disk surface in a circumferential direction; and (b) differently setting the BPI on the disk surface based on the measured read/write performance. 
         [0036]    In step (a), Over Write (OW) or Bit Error Rate (BER) on the disk surface in a circumferential direction may be measured. 
         [0037]    In step (b), target OW or BER preset based on a BPI reference value on the disk surface in a circumferential direction, may be compared with OW or BER measured per servo signal, thereby calculating a changed amount of the OW or the BER. Then, BPI based on the calculated changed amount of the OW or the BER may be set as corrected BPI per servo signal. 
         [0038]    The method may further comprise, when a read/write operation is performed as the HDD operates, providing BPI based on corrected BPI per servo signal, to a corresponding servo signal. 
         [0039]    The corrected BPI may be stored in a BPI table. 
         [0040]    In step (b), BPI based on a changed amount of OW or BER measured per zone may be set as corrected BPI per zone, said each zone obtained by dividing the disk in a radial direction or a circumferential direction. 
         [0041]    The method may further comprise, when a read/write operation is performed as the HDD operates, providing BPI based on corrected BPI per zone, to a corresponding zone. 
         [0042]    To achieve these and other advantages as embodied and broadly described herein, there is also provided a hard disk drive (HDD), comprising: a disk having a magnetic recording layer recorded on its surface; a head stack assembly (HSA) having a magnetic head for writing or reading data onto/from the disk; and a controller configured to measure a read/write performance on the disk surface in a circumferential direction, and to differently set Bits Per Inch (BPI) of the disk surface based on the measured read/write performance. 
         [0043]    The read/write performance may be Over Write (OW) or Bit Error Rate (BER) on the disk surface in a circumferential direction. 
         [0044]    The controller may calculate a changed amount of OW or BER, by comparing target OW or BER preset based on a BPI reference value on the disk surface in a circumferential direction, with OW or BER measured per servo signal. Then, the controller may control BPI based on the calculated changed amount of the OW or the BER to be set as corrected BPI per servo signal. 
         [0045]    When a read/write operation is performed as the HDD operates, the controller may provide BPI based on corrected BPI per servo signal, to a corresponding servo signal. 
         [0046]    The controller may control BPI based on a changed amount of OW or BER measured per zone, to be set as corrected BPI per zone, said each zone obtained by dividing the disk in a radial direction or a circumferential direction. 
         [0047]    When a read/write operation is performed as the HDD operates, the controller may provide BPI based on corrected BPI per zone, to a corresponding zone. 
         [0048]    The embodiments disclosed herein may have the following advantages. 
         [0049]    Since BPI on the disk in a circumferential direction may be differently controlled based on a read/write performance difference due to non-uniformity on the disk surface, a capacity can be increased and reliability can be enhanced. 
         [0050]    Further scope of applicability of the present application will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating some embodiments, are given by way of illustration only, since various changes and modifications within the scope of the embodiments will become apparent to those skilled in the art from the detailed description. 
         [0051]      FIG. 4  is a partial disassembled perspective view of an HDD to which a BPI control method for a disk according to a first embodiment. 
         [0052]    Referring to  FIG. 4 , the HDD  1  according to the first embodiment may comprise a disk pack  10  including a disk  11  configured to record and store data, and a spindle motor  12  configured to support and rotate the disk  11 ; a head stack assembly (HSA)  20  configured to read data on the disk  11 ; a base  30  onto which the above components are assembled; a printed circuit board assembly (PCBA)  40  coupled to a lower part of the base  30 , and configured to control each type of components by mounting circuitry components onto a printed circuit board (PCB); and a cover  50  configured to cover the base  30 . 
         [0053]    The head stack assembly  20  is a carriage for writing (recording) data onto the disk  11 , or reading out data on the disk  11 . Such HSA is also referred to as an actuator. 
         [0054]    The HSA  20  includes a magnetic head  21  for recording data onto the disk  11  or reading out data on the disk  11 , an actuator arm  23  which moves or pivots with respect to the disk  11  around a pivot shaft  22  as a pivoting center so that the magnetic head  21  can access data on the disk  11 , a pivot shaft holder  24  configured to rotatably support the pivot shaft  22 , and to which the actuator arm  23  is coupled for support, and a bobbin (not shown) disposed at the pivot shaft holder  24  in the opposite direction to the actuator arm  23 , and on which a voice coil motor (VCM) coil (not shown) is wound so as to be located between magnets. 
         [0055]    The magnetic head  21  is configured to detect a magnetic field formed on the surface of the disk  11 , or to read or write data on the rotating disk  11  by magnetizing the surface of the disk  11 . Such magnetic head  21  is categorized into a read head for reading data on a track, and a write head for writing data onto a track. 
         [0056]    The voice coil motor  25  is a type of driving motor for rotating the actuator arm  23  so that the magnetic head  21  can be moved to a desired position on the disk  11 . More specifically, the voice coil motor  25  is operated according to Fleming&#39;s left-hand rule, whereby a force is generated when current flows in a conductive body existing in a magnetic field. That is, the voice coil motor  25  pivots a bobbin by applying a force to the bobbin upon applying current to a VCM coil located between magnets. Under this configuration, the actuator arm  23  extending from the pivot shaft holder  24  in the opposite direction to the bobbin rotates, and the magnetic head  21  supported by an end portion of the actuator arm  23  moves on the rotating disk  11  in a radial direction. The magnetic head  21  searches for one or more tracks while moving on the disk  11  in a radial direction, and accesses information. The accessed information is signal-processed. 
         [0057]    The PCBA  40  may include a controller  42  (refer to  FIG. 8 ) configured to control each type of components and to control a BPI on the disk  11  in a circumferential direction, and one or more memories (not shown) configured to store therein a BPI table. 
         [0058]      FIG. 5  is a schematic planar view of a disk region,  FIG. 6  is a view illustrating a data format of each track, and  FIG. 7  is a view illustrating a detailed configuration of a servo sector. 
         [0059]    As shown in  FIG. 5 , the disk  11  for recording data thereon includes tracks  13  serving as an object for storing servo information and data information, and sectors  14  in the form of unit objects and obtained by dividing the track  13  at the same interval on the basis of a rotation shaft center. 
         [0060]    As shown in  FIG. 6 , a servo sector  15  to which a servo signal for servo controls such as track seeking or track following is applied, and a data sector  17  for recording a user&#39;s data are alternately disposed on each track  13 . 
         [0061]    As shown in  FIG. 7 , each servo sector  15  includes a preamble  15   a , a Servo Address Mark (SAM)  15   b , a gray code  15   c , a sector code  15   d , burst signals A, B, C and D  15   e , and a PAD  15   f.    
         [0062]    The preamble  15   a  is configured to provide a clock synchronization when reading servo information according to a servo signal, and to provide a gap in front of the servo sector for indication of the servo sector. The preamble  15   a  is also called as servo sync. The SAM  15   b  is configured to inform start of a servo, and to provide synchronization for reading the subsequent gray code  15   c . That is, the SAM  15   b  serves as a reference point for generating each type of timing pulses associated with servo controls. The gray code  15   c  provides information on each track  13 , i.e., track information. The sector code  15   d  provides a sector number. The burst signals A, B, C and D  15   e  provide position Error Signals (PES) required for track search. And, the PAD  15   f  provides a transition margin from the servo sector to the data sector. 
         [0063]    The data sector  17  is positioned before and after the servo sector  15 . And, the data sector  17  is categorized into an ID field  17   a  and a data field  17   b.    
         [0064]    Header information for identifying a corresponding data sector is recorded on the ID field  17   a . And, digital data desired by a user is recorded on the data field  17   b.    
         [0065]      FIG. 8  is a schematic control block diagram of the HDD shown in  FIG. 4 . 
         [0066]    Referring to  FIG. 8 , the HDD  1  according to one embodiment includes a preamp  53 , a read/write channel  54 , a host interface  55 , a VCM driver  50 , an SPM driver  56 , a status estimator  57 , and a controller  42 . 
         [0067]    The preamp (pre-AMP)  53  is configured to record data on the disk  11  by amplifying a data signal reproduced from the disk  11  by the magnetic head  21 , or by amplifying recording current converted by the read/write channel  54  by the magnetic head  21 . 
         [0068]    The read/write channel  54  is configured to convert a signal amplified by the preamp  53  into a digital signal, and to transmit the digital signal to a host device (not shown) via the host interface  55 . Alternatively, the read/write channel  54  is configured to receive a user input data via the host interface  55 , to convert the received data into a binary data stream which can be easily recorded, and to input the binary data stream to the preamp  53 . 
         [0069]    The host interface  55  is configured to transmit digital signal-converted data to the host device. Alternatively, the host interface  55  is configured to receive a user input data from the host device, and to input the received user input data to the read/write channel  54  by the controller  42 . 
         [0070]    The VCM driver  50  is configured to control the amount of current applied to the voice coil motor  25  by receiving a control signal of the controller  42 . 
         [0071]    The SPM driver  56  is configured to control the amount of current applied to the spindle motor  12  by receiving a control signal of the controller  42 . 
         [0072]    The status estimator  57  is configured to estimate a status variable value of a movement of the magnetic head  21 , such as a position, a speed and control input information of the magnetic head  21 , based on a status equation indicated by Position Error Signal (PES). 
         [0073]    The controller  42  of the HDD  1  is configured to control BPI on the disk  11  in a circumferential direction. 
         [0074]    More specifically, the controller  42  controls BPI on the surface of the disk  11  in a circumferential direction (b) to be differently set, whereas BPI on the surface of the disk  11  in a circumferential direction (b) (refer to  FIG. 5 ) is set to be equal in the conventional art. 
         [0075]    As aforementioned, since the disk surface is non-uniform, a read/write performance difference occurs in a circumferential direction (b). With consideration of such phenomenon, the controller  42  controls BPI on the disk surface in a circumferential direction to be differently set based on a measured read/write performance. 
         [0076]    The read/write performance, i.e., the read/write characteristics may be various factors. Hereinafter, it is assumed that the read/write performance is OW (Over Write) or BER (Bit Error Rate) on the disk surface in a circumferential direction. The OW on the disk surface in a circumferential direction may indicate a successful degree of data writing, and the BER on the disk surface in a circumferential direction may indicate an error rate during a read operation. 
         [0077]    The controller  42  compares target OW or BER preset based on a BPI reference value of the disk surface in a circumferential direction, with OW or BER measured per servo signal, thereby calculating a changed amount of the OW or the BER. Then, the controller  42  controls BPI based on the calculated changed amount of the OW or the BER to be set as corrected BPI per servo signal. 
         [0078]    The BPI reference value is predefined while manufacturing the disk  11 . In the conventional art, a BPI reference value is used without a change, resulting in capacity deficiency and reliability degradation. 
         [0079]    When a read/write operation is performed as the HDD  1  operates, the controller  42  provides BPI based on corrected BPI per servo signal, to a corresponding servo signal. 
         [0080]    More specifically, the OW and the BER on the disk surface in a circumferential direction are substantially proportional to each other (refer to  FIG. 3 ). Accordingly, on the disk surface having low OW, BPI is lowered to reduce an error rate and to enhance reliability. On the other hand, on the disk surface having high OW, BPI is increased to enhance a capacity. Once BPI is increased, a capacity can be increased due to a reduced data size. 
         [0081]    As BPI on the disk surface in a circumferential direction can be differently set, a capacity can be increased and reliability can be enhanced. 
         [0082]    Such operation of the controller  42  will be explained in more details with reference to  FIG. 9 . 
         [0083]      FIG. 9  is a flowchart illustrating a BPI control method for a disk in a circumferential direction. 
         [0084]    Firstly, OW or BER of the disk surface in a circumferential direction is measured per servo signal (S 11 ). 
         [0085]    As the measured information is recorded, distributions of the OW or the BER of the disk surface in a circumferential direction can be checked. Here, the OW or the BER may be OW or BER per unit sector on the disk surface in a circumferential direction. 
         [0086]    Then, a changed amount of OW or BER is calculated, by comparing target OW or BER preset based on a BPI reference value of the disk surface in a circumferential direction, with OW or BER measured per servo signal. Then, BPI based on the calculated changed amount of the OW or the BER is set as corrected BPI per servo signal (S 12 ). 
         [0087]    Next, S 12  will be explained in more details. 
         [0088]    More specifically, while a subsequent servo signal is being read from a servo signal having a value lower than that of target OW or BER preset based on a BPI reference value, i.e., while each sector is being read in a circumferential direction, OW or BER is measured in a state where BPI is decreased into a value lower than the BPI reference value. Such process may be repeatedly performed. 
         [0089]    On the contrary, while a subsequent servo signal is being read from a servo signal having a value higher than that of target OW or BER, OW or BER is measured in a state where BPI is increased into a value higher than the BPI reference value. Such process may be also repeatedly performed. 
         [0090]    If a changed amount of OW or BER is calculated by comparing such measured OW or BER with target OW or BER preset based on a BPI reference value, corrected BPI based on the changed amount of the OW or BER can be obtained. The corrected BPI can be set as corrected BPI per servo signal. 
         [0091]    Here, the corrected BPI may be a BPI reference value, or may be larger or smaller than the BPI reference value. Alternatively, the corrected BPI may be stored in a memory or in a maintenance region of the disk  11  in the form of a BPI table. 
         [0092]    Then, when a read/write operation is performed as the HDD  1  operates, the controller  42  provides BPI based on corrected BPI on the BPI table, per servo signal, to a corresponding servo signal (S 13 ). 
         [0093]    In the preferred embodiment, since BPI on the disk  11  in a circumferential direction can be differently controlled based on a read/write performance difference due to non-uniformity on the disk surface, a capacity can be increased and reliability can be enhanced. 
         [0094]      FIG. 10  is a flowchart illustrating a BPI control method for a disk in a circumferential direction according to a second embodiment, and  FIG. 11  is a schematic planar view of a disk region to which the control method of  FIG. 10  is applied. 
         [0095]    As shown in  FIG. 11 , BPI of a disk  11   a  in a circumferential direction is differently controlled by dividing the disk  11   a  in the form of a two-dimensional (2D) zone map formed in a radial direction (a) and a circumferential direction (b). A plurality of zones are regularly disposed on the zone map of  FIG. 11 . 
         [0096]    Referring to  FIG. 10 , a 2D zone map (refer to  FIG. 11 ) formed in a radial direction (a) and a circumferential direction (b) is created (S 21 ). 
         [0097]    Then, OW or BER on the surface of the disk  11   a  in a circumferential direction is measured per zone (S 22 ). The measured information is recorded to allow OW or BER distribution to be checked on the disk surface in a circumferential direction. 
         [0098]    Then, BPI based on a changed amount of OW or BER obtained per zone is set as corrected BPI, said each zone obtained by dividing the disk  11   a  in a radial direction or a circumferential direction (S 23 ). 
         [0099]    When a read/write operation is performed as the HDD  1  operates, the controller  42  provides BPI based on corrected BPI on the BPI table, per zone, to a corresponding zone (S 24 ). Here, the same BPI is provided to all the positions inside a corresponding zone. 
         [0100]      FIG. 12  is a schematic planar view of a disk region to which a BPI control method for a disk according to a third embodiment. 
         [0101]    In  FIG. 11 , zones on a zone map are regularly divided from each other. However, in case of a disk  11   b  of  FIG. 12 , zones on a zone map are irregularly divided from each other. The embodiment disclosed herein may be also applied to  FIG. 12 . 
         [0102]    One embodiment may be a method comprising (a) measuring read/write performance on a disk surface in a circumferential direction, and (b) differently setting BPI on the disk surface in a circumferential direction based on the measured read/write performance. An embodiment may also include wherein in step (a), Over Write (OW) or Bit Error Rate (BER) on the disk surface in a circumferential direction is measured. An embodiment may also include wherein in step (b), target OW or BER preset based on a BPI reference value of the disk surface in a circumferential direction, is compared with OW or BER measured per servo signal thus to calculate a changed amount of the OW or the BER, and then BPI based on the calculated changed amount of the OW or the BER is set as corrected BPI per servo signal. An embodiment may further comprise, when a read/write operation is performed as the HDD operates, providing BPI based on corrected BPI per servo signal, to a corresponding servo signal. An embodiment may also include wherein the corrected BPI is stored in a BPI table. An embodiment may also include, wherein in step (b), BPI based on a changed amount of OW or BER measured per zone is set as corrected BPI per each zone, said each zone obtained by dividing the disk in a radial direction or a circumferential direction. An embodiment may further comprise, when a read/write operation is performed as the HDD operates, providing BPI based on corrected BPI per zone, to a corresponding zone. 
         [0103]    In another embodiment, a device may comprise a disk having a magnetic recording layer recorded on its surface, a head stack assembly (HSA) having a magnetic head for writing or reading data onto/from the disk, and a controller configured to measure read/write performance on the disk surface in a circumferential direction, and to differently set Bits Per Inch (BPI) of the disk surface based on the measured read/write performance. An embodiment may also include, wherein the read/write performance is Over Write (OW) or Bit Error Rate (BER) on the disk surface in a circumferential direction. An embodiment may also include, wherein the controller is configured to calculate a changed amount of OW or BER, by comparing target OW or BER preset based on a BPI reference value of the disk surface in a circumferential direction, with OW or BER measured per servo signal, and then the controller is configured to control BPI based on the calculated changed amount of the OW or the BER to be set as corrected BPI per servo signal. An embodiment may also include, wherein when a read/write operation is performed as the HDD operates, the controller provides BPI based on corrected BPI per servo signal, to a corresponding servo signal. An embodiment may also include, wherein the controller is configured to control BPI based on a changed amount of OW or BER measured per zone, to be set as corrected BPI per zone, said each zone obtained by dividing the disk in a radial direction or a circumferential direction. An embodiment may also include, wherein when a read/write operation is performed as the HDD operates, the controller provides BPI based on corrected BPI per zone, to a corresponding zone. 
         [0104]    The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the inventive concepts herein. The present teachings can be readily applied to other types of apparatuses. This description is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. The features, structures, methods, and other characteristics of the exemplary embodiments described herein may be combined in various ways to obtain additional and/or alternative exemplary embodiments. 
         [0105]    As the present features may be embodied in several forms without departing from the characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalents of such metes and bounds are therefore intended to be embraced by the appended claims.