Patent Publication Number: US-2009237829-A1

Title: Information recording medium

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2008-069356, filed on Mar. 18, 2008, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are directed to an information recording medium and an information storage device having the information recording medium. 
     BACKGROUND 
     Attention is recently paid to a patterned media type magnetic disk as a technique for improving the recording density of an information recording medium mounted on an information storage device. The patterned media type magnetic disk has a structure in which dots each made of a magnetic material for storing a minimum unit of information are arranged in a regular array on the disk. 
       FIG. 1  is a perspective view schematically illustrating the structure of a patterned media type magnetic disk. Illustrated in  FIG. 1  is apart cut from a disk-shaped magnetic disk. 
     A magnetic disk D illustrated in  FIG. 1  has a structure in which plural recording dots Q are arranged in a regular array on a substrate S, and information corresponding to one bit is magnetically recorded on each of the recording dots Q. The recording dots are arranged circumferentially around the center of a disk, and a row of the recording dots forms a track T. Such a patterned media type magnetic disk is generally manufactured by a publicly known manufacturing process called “nanoimprint lithography”. Since the present invention does not directly relate to a manufacturing process, description on the manufacturing process is omitted. 
     A magnetic disk device having a general magnetic disk, not limited to a patterned media type one, mounted thereon records and reproduces target information by positioning a magnetic head using a servo pattern on the magnetic disk. On a track of the magnetic disk, a servo region in which a servo pattern is arranged and a data region in which data is recorded are alternately arranged along the track. From the magnetic head relatively moving along the track of the rotating magnetic disk, a servo pattern is read at a servo sampling frequency represented by (the number of servo regions per rotation×the number of rotations of the magnetic disk) to obtain position information of the magnetic head. Based on the position information, servo control in a discrete time region is performed, so that the magnetic head follows the target track. 
       FIGS. 2A and 2B  illustrate general arrangement of regions in a magnetic disk. The regions of a magnetic disk  90  are illustrated together with a magnetic head in  FIG. 2A , and a partial region R of the magnetic disk  90  is illustrated in linear development in  FIG. 2B  on an enlarged scale. 
     The regions on the magnetic disk  90  are partitioned into plural zones from a zone  0  to a zone i in the radius direction, and are used. In one zone, the length of a recording region per bit gradually becomes long from the inner round towards the outer round because the recording frequency is constant. However, in order to restrict the length of the recording region per bit for every zone within a given range, a structure (zoned CAV method) is employed in which the further outside the zone is positioned, the higher the recording frequency is. A sector is composed of a servo region and a data region following this servo region. Note that as illustrated in  FIG. 2A , a magnetic head  91  is attached to the leading edge of an arm  92 , and strictly speaking, a servo region is arranged in a circular-arc shape along a locus  93  of the magnetic head moving in accordance with rotation of the arm. 
     As opposed to the patterned media type magnetic disk, in a continuous media type magnetic disk that has been widely used, a servo region and a data region are provided in a magnetic film extending uniformly and continuously. On the other hand, in the patterned media type magnetic disk, a pattern of magnetic area/non-magnetic area in accordance with servo information has been formed in a servo region by the manufacturing process, and becomes a magnetic pattern representing the servo information when the entire servo region is uniformly magnetized. Minute recording dots are discretely arranged in a data region. One recording dot corresponds to one bit of information, and the bit value is represented by the magnetizing direction. In the patterned media type magnetic disk, information cannot be recorded between recording dots, and therefore recording of information needs to be performed after a magnetic head has been positioned accurately above the a recording dot. This positioning includes positioning a recording head in the radius direction of a magnetic disk and synchronizing the timing of supplying a signal to the recording head and the timing of reading a signal from the recording head with the timing of passing the recording dot. 
       FIG. 3  explains the relationship between recording dots of a patterned media type magnetic disk and write clocks. 
     As illustrated in  FIG. 3 , when recording information on a patterned media type magnetic disk, it is necessary to generate a write clock in synchronization with a timing at which the magnetic head  95  passes the recording dot Q and to supply write data to the magnetic head  95  in synchronization with the write clock. The synchronization used here includes the same period and the same phase. For example, both the periods of a write clock C 1  and a write clock C 2  illustrated in  FIG. 3  are the same as the period in which the magnetic head  95  passes the recording dot Q, but the phases of the write clock C 1  and the write clock C 2  deviate from each other. As a result, if a signal is supplied to the magnetic head  95  based on the timing of the appropriate write clock C 1 , information is recorded on the recording dot Q; however, if a signal is supplied based on the timing of the inappropriate write clock C 2 , information is not normally recorded. 
     As a technique for producing a write clock in synchronization with a timing of passing a recording dot, a technique of providing a write preamble serving as the timing reference on a magnetic disk is proposed, e.g., in Japanese Laid-open Patent Publication No. 2003-157507. 
       FIG. 4  illustrates part of a patterned media type magnetic disk in which a write preamble is provided. 
     On the magnetic disk illustrated in  FIG. 4 , a write preamble  96  made of a pattern of a magnetic material is provided adjacent to a data region. If a read head for reading information of a magnetic disk device is also used as a write head that writes information, a write clock having a period and a phase in synchronization with a signal read when the head passes the write preamble  96  can be generated. 
     However, with a magnetic disk device in which a read head and a write head are separately provided in a magnetic head, synchronization is more difficult. In a magnetic head illustrated in  FIG. 4 , a read head  98   a  and a write head  98   b  are separately provided. A distance G between the read head  98   a  and the write head  98   b  generally corresponds to several tens of tracks, and has a deviation for each product. The read head  98   a  and the write head  98   b  are attached to a rotating arm  99  to be arranged obliquely to the track, and therefore effects of the distance G between the read head  98   a  and the write head  98   b  and the deviation appear both in the circumferential direction along which recording dots are arranged and in the radius direction that intersects the circumferential direction. 
     In a magnetic disk device having a configuration where a read head and a write head are separated, when a write preamble is read by the read head and a write clock is locked to the read signal by a phase locked loop (PLL) circuit or the like, the period of the write clock (C 4  of  FIG. 4 ) becomes the same as the period of a timing (C 3  of  FIG. 4 ) at which the write head passes a recording dot, but their phases do not become the same. For example, in Japanese Laid-open Patent Publication No. 2006-164349, in order to adjust the positional relationship in the circumferential direction, i.e., to adjust the phase difference between the write clock and the timing of passing a recording dot, a method is proposed that records information while changing the phase of the write clock to search for the optimum phase. 
     Regarding the deviation in the radius direction, there is a problem specific to a patterned media type magnetic disk in addition to one with a continuous media type magnetic disk. As described above, the distance G between the read head  98   a  and the write head  98   b  generally corresponds to several tens of tracks, and has a deviation for each product. This state is the same as in a continuous media type magnetic disk. In the continuous media type magnetic disk, however, a write head is positioned at an arbitrary position and information is recorded as trial write, and thereafter the recorded information is read while the position of a read head is changed in N ways to detect the position at which signals representing information are most efficiently read, thus enabling the distance G (see  FIG. 4 ) between the read head  98   a  and the write head  98   b  to be accurately measured. If G is measured, appropriate recording is enabled by adjustment of a relative positional relationship between the write head and the read head. For measurement of G, it is necessary to perform recording corresponding to one rotation of a magnetic disk and to read information while changing the position of a read head in N ways. Given that one disk rotation is needed to read information for one way of the position of the read head, the number of rotations NT of the magnetic disk needed to obtain an appropriate position of the magnetic head is expressed by the following. 
         NT= 1 +N    
     In contrast, in the patterned media type magnetic disk, for example, when the first trial write is performed to a portion between recording dots, this may result in a failure to record information on a recording dot although the phase of a write clock in the circumferential direction is proper. In this case, the relative distance G (see  FIG. 4 ) cannot be measured by trial of NT (=1+N) rotations. 
     Thus, in the patterned media type magnetic disk, the positional relationship needs to be adjusted both in the circumferential direction and in the radius direction. 
     In the patterned media type magnetic disk, however, there are two conditions for disk access that are to be adjusted, i.e., the phase of a write clock and the positional relationship in the radius direction between a write head and a recording dot. This increases combination patterns of access conditions to be changed in trial write and read. For example, even though the period and the phase of a write clock are appropriate, there is no assurance that information is recorded on recording dots. In addition, it cannot be determined whether the cause of information not recorded on recording dots is a deviation in the radius direction or a deviation in the circumferential direction, i.e., a phase deviation of a write clock. 
     If assuming that the position of a read head is changed over N tracks, the position in the radius direction of a write head is changed in M ways, and the phase of a write clock is changed in L ways, the optimum access conditions are to be determined among these conditions, the needed number of rotation NT of a magnetic disk is expressed by the following. 
         NT =(1 +N )× M×L    
     Therefore, there is a problem in that a long time is needed for determining the optimum access conditions in an adjustment. 
     SUMMARY 
     An information recording medium, includes: a substrate; first recording dots which are arranged in an array circumferentially in accordance with a predetermined regulation at mutual intervals in accordance with the regulation at a position in accordance with the regulation and are used to magnetically record information; and second recording dots which are arranged in an array circumferentially in accordance with the regulation at mutual intervals in accordance with the regulation, in which plural kinds of positions having different deviation amounts from the position in accordance with the regulation appear in one round of the array, and which are used to magnetically record information. 
     Objects and advantages of the embodiments will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view schematically illustrating the structure of a patterned media type magnetic disk; 
         FIGS. 2A and 2B  illustrate general arrangement of regions in the magnetic disk; 
         FIG. 3  explains the relationship between recording dots of a patterned media type magnetic disk and write clocks; 
         FIG. 4  illustrates part of a patterned media type magnetic disk in which a write preamble is provided; 
         FIG. 5  illustrates a hard disk device (HDD) being a specific first embodiment of an information storage device; 
         FIG. 6  illustrates the details of the magnetic disk illustrated in  FIG. 5 ; 
         FIG. 7  is a flow chart for explaining the process of determining the optimum access conditions to the magnetic disk illustrated in  FIG. 6  in the magnetic disk device illustrated in  FIG. 5 ; 
         FIG. 8  illustrates a magnetic disk of a HDD being a specific second embodiment of the information storage device; 
         FIG. 9  is a flow chart for explaining the process of determining the optimum access conditions to the magnetic disk illustrated in  FIG. 8 ; 
         FIG. 10  illustrates a magnetic disk of a HDD being a specific third embodiment of the information storage device; 
         FIG. 11  is a flow chart for explaining the process of determining the optimum access conditions to the magnetic disk illustrated in  FIG. 10 ; 
         FIG. 12  illustrates a magnetic disk of a HDD being a specific fourth embodiment of the information storage device; and 
         FIG. 13  is a flow chart for explaining the process of determining the optimum access conditions to the magnetic disk illustrated in  FIG. 12 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Specific embodiments of an information recording medium and an information storage device will be described below with reference to the drawings. 
       FIG. 5  illustrates a HDD being the specific first embodiment of the information storage device. 
     A HDD  1  includes a disk-shaped magnetic disk  2 , a magnetic head  3  that reads and writes information on the magnetic disk  2 , an arm  4  that moves the magnetic head  3  in the radius direction of the magnetic disk, an arm drive section  5  that rotates and drives the arm  4 , and a control circuit  6  that controls components of the HDD  1  and that receives and transmits signals from and to the magnetic head  3 . The magnetic disk  2  corresponds to one example of the information recording medium described above. The magnetic head  3  includes a read head  3   a  and a write head  3   b , and the read head  3   a  and the write head  3   b  are disposed with an interval there between. 
     The control circuit  6  includes a read section  6   a  that receives signals output from the read head  3   a , a write section  6   c  that supplies to the write head  3   b  signals of information to be recorded, a clock generation section  6   b  that supplies a read clock to the read section  6   a  and supplies a write clock to the write section  6   c , and a control section  6   f  that controls the whole control circuit  6  and that drives the arm drive section  5  to move the magnetic head  3 . The read section  6   a  supplies to the clock generation section  6   b  signals that are read when the read head  3   a  passes a write preamble. The clock generation section  6   b  has a PLL circuit, and generates a read clock having a period and a phase that are the same as those of a signal of a write preamble supplied from the read section  6   a  and also generates a write clock being identical in period and shifted in phase to the signal of the write preamble. The shift in phase between the read clock and the write clock is set by the control section  6   f . The control section  6   f  has a memory, and stores the amplitude of a read signal of a recording dot supplied from the read section  6   a , determines conditions in which the amplitude becomes maximum, and, based on the determined conditions, sets the positions of the read head  3   a  and the write head  3   b  by drive of the arm drive section  5  and the amount of phase shift of the write clock. 
     The magnetic disk  2  is a patterned media type magnetic disk, and its basic structure having a substrate S and plural recording dots Q arrayed on the substrate S is the same as that described referring to  FIG. 1 . 
       FIG. 6  illustrates the details of the magnetic disk illustrated in  FIG. 5 . A half of the magnetic disk  2  is illustrated in Part (A) of  FIG. 6 , and tracks in plural portions on the magnetic disk  2  are illustrated in linear development in Parts (B) to (E) of  FIG. 6  on an enlarged scale. 
     On the magnetic disk  2 , tracks T (T x , T x+1 , T x+2 , . . . , T y , T y+1 , T y+2 , . . . ) are formed of rows of recording dots arranged on the circumferences. Each track is separated by a servo region  21  in which a servo pattern is arranged. In the track, a portion from one servo region to just in front of the next servo region is termed a “sector”. In an example of magnetic disk  2  illustrated in  FIG. 6 , P sectors are provided and numbers from 0 (zero) to (P−1) are assigned to the sectors. Each sector has the servo region  21 , a preamble region  22  and a data recording region  23 . In the example of the magnetic disk  2  illustrated in  FIG. 6 , the preamble region  22  is disposed between the servo region  21  and the data recording region  23 . The regions on the magnetic disk  2  are partitioned into plural zones from the zone “ 0 ” to the zone “i” in the radius direction. Each zone has a trial write region  24  and an information storage region  25 , and the trial write region  24  and the information storage region  25  partition each zone in the radius direction. In the example of the magnetic disk  2  illustrated in  FIG. 6 , among plural tracks belonging to each zone, inside tracks T x , T x+1 , T x+2 , . . . belong to the information storage region  25  and outside tracks T y , T y+1 , T y+2 , . . . belong to the trial write region  24 . Both a track belonging to the trial write region  24  and a track belonging to the information storage region  25  each have P sectors from the 0th sector to (P−1) th sector. Each sector has the servo region  21 , the preamble region  22  and the data recording region  23 . Formed in the servo region  21  is a pattern made of a magnetic material. The pattern is magnetized upon manufacturing of the magnetic disk  2  to form a magnetic pattern representing information for identifying the track T. Formed in the preamble region  22  are write preambles  27  for generating a reference for the timing for writing information. The write preambles  27  are formed of a pattern made of a magnetic material. The pattern is magnetized upon manufacturing of the magnetic disk  2  to form a magnetic pattern. The write preambles  27  are written at least in the trial write region  24  and the information storage region  25  with the common period and the common phase. Arranged in the data recording region  23  are recording dots made of a magnetic material in which information is stored. Illustrated in Part (B) of  FIG. 6  are the write preambles  27  and the first recording dots  26 A in the sector  0  of tracks T x , T x+1 , T x+2 , . . . provided in the information storage region  25  of the zone  1  of the magnetic disk  2 . 
     The first recording dots  26 A are arranged in an array circumferentially in accordance with a predetermined regulation. In more detail, the first recording dots  26 A are arranged on plural concentric tracks T (T x , T x+1 , T x+2 , . . . ). The first recording dots  26 A are arrayed, in one zone, at mutual intervals in accordance with the predetermined regulation to allow reading with a common read clock and writing with a common write clock. In more detail, in one zone, the same number of first recording dots  26 A are arranged in each track T (T x , T x+1 , T x+2 , . . . ). That is, the first recording dots  26 A are arranged, in one zone, at regular mutual intervals with respect to an angle θ from the center of the magnetic disk  2 , i.e., at equiangular intervals. With attention given to the individual track T (T x , T x+1 , T x+2 , . . . ), the first recording dots  26 A are arranged at equal intervals on the track T. When in the HDD  1 , the magnetic disk  2  rotates for the read head  3   a  or the write head  3   b  to relatively move on the track T, the time period in which the read head  3   a  or the write head  3   b  passes the recording dot  26 A is constant in any track T in one zone. Therefore, the interval between the recording dots  26 A adjacent to each other in the circumferential direction in one zone is termed a “period λ” in the meaning that the time period for passing a head is equal. Further, the first recording dots  26 A are arrayed at a position in accordance with the regulation. In more detail, all the first recording dots  26 A are arranged at equiangular intervals and are arranged on circular tracks. The fact that all the first recording dots  26 A arranged at equiangular intervals means that the first recording dots  26 A are at a reference position arranged in the period λ on tracks. 
     The write preambles  27  as viewed in the circumferential direction are arranged at regular mutual intervals with respect to the angle θ from the center of the magnetic disk  2 . In an example illustrated in  FIG. 6 , the write preambles  27  are arrayed at mutual intervals having a relationship of 1:1 to those of the first recording dots  26 A on the same track. That is, the write preambles  27  are arranged with the period λ. Also, at a position where the write preamble  27  and the first recording dot  26 A are adjacent to each other, the write preamble  27  and the first recording dot  26 A are arrayed at an interval of the period λ. That is, the write preambles  27 , just as the first recording dots  26 A, are on the reference position arranged with the period λ on a track. This means that the first recording dots  26 A and the write preambles  27  are arranged at the position with a phase difference of 0 degree with respect to the period λ of the array. 
     Accordingly, in the case where the read head  3   a  of the magnetic disk device  1  relatively moves along any one of the tracks T (T x , T x+1 , T x+2 , . . . ) illustrated in Part (B) of  FIG. 6 , when a read clock having a period and a phase in synchronization with a signal read from the read head  3   a  passing the write preamble  27  is generated, the period and phase of the read clock are the same as those of the timing at which the read head  3   a  passes the first recording dot  26 A. Reading from the first recording dot  26 A can therefore be performed in synchronization with the read clock that is in synchronization with the read signal of the write preamble  27 . However, the read head  3   a  and the write head  3   b  are distant from each other, and therefore the phase of the read clock is not the same as that of the timing at which the write head  3   b  passes the first recording dot  26 A. In order to appropriately record information on the first recording dot  26 A, a write clock having the same phase as that of the timing at which the write head  3   b  passes the first recording dot  26 A is needed. 
     As illustrated in Parts (C) to (E) of  FIG. 6 , second recording dots  26 B,  26 C and  26 D are arrayed following the write preambles  27  on the tracks T y , T y+1 , T y+2 , . . . in the trial write region  24 . 
     The second recording dots  26 B in the sector  0  in the trial write region  24  are arranged in an array, circumferentially in accordance with the same predetermined regulation as that of the first recording dots  26 A arranged in the information storage region  25 , at mutual intervals in accordance with the regulation at a position in accordance with the regulation. Accordingly, the second recording dots  26 B are arranged at a position with a phase difference of 0 degree with respect to the write preambles  27 . 
     On the other hand, the second recording dots  26 C in a sector  1  in the trial write region  24  are arranged in an array circumferentially in accordance with the same predetermined regulation as that of the second recording dots  26 B arranged in the sector  0  at mutual intervals in accordance with the regulation; however, they are arranged at a position deviating in a direction along the round of the array from the position in accordance with the regulation. In more detail, the second recording dots  26 C in the sector  1  are arranged with a phase shift of 360/P degrees with respect to the reference position with the period λ following the write preambles  27  on the track. That is, the second recording dots  26 C in the sector  1  are arranged at a position with a phase difference of 360/P degrees with respect to the write preambles  27 . 
     The second recording dots  26 B,  26 C and  26 D in the trial write region  24  appear at plural positions with different deviation amounts. In more detail, the deviation amounts of the second recording dots  26 B,  26 C and  26 D with respect to the reference position with the period λ following the write preambles  27  increase by 360/P degrees per sector. For example, as illustrated in Part (E) of  FIG. 6 , the second recording dots  26 D in a sector “p” are arranged at a position with a phase difference of 360p/P degrees with respect to the write preambles  27 . 
     Here, description is given on a process of determining the optimum access conditions to the first recording dots  26 A in the information storage region  25  with the magnetic disk device  1  illustrated in  FIG. 5 . 
       FIG. 7  is a flow chart for explaining the process of determining the optimum access conditions to the magnetic disk illustrated in  FIG. 6  in the magnetic disk device  1  illustrated in  FIG. 5 . In this process, data is read and written while each of the track read by the read head  3   a , the position in the radius direction of the write head  3   b , and the phase of a write clock is gradually changed, thereby determining conditions in which the amplitude of a signal read from the read head  3   a  becomes maximum. 
     If the phase of a timing at which the write head  3   b  passes a recording dot and the phase of a write clock become the same, and the shifted position in the radius direction of the write head  3   b  and the track T y  become the same, the recording efficiency of information, that is, the degree to which a recording dot is magnetized becomes maximum. In the process of  FIG. 7 , access conditions are determined in which the signal amplitude value becomes maximum. 
     First, the control section  6   f  of the control circuit  6  sets an initial phase, which is an initial value of the phase difference between a read clock and a write clock, in a clock generation section  6   b  (S 11 ). The phase difference is to be changed later, and therefore an arbitrary value can be selected as the initial value. For example, if 0 is set as the initial value, the read clock and the write clock generated by the clock generation section  6   b  have the same phase. 
     Next, the control circuit  6  drives the arm drive section  5  to move the write head  3   b  of the magnetic head  3  to the initial position of trial write (S 12 ). Specifically, the write head  3   b  is moved with the objective of any track, e.g., the track T y , in the trial write region  24 . Movement of the write head  3   b , in more detail, is performed by positioning the read head  3   a  so that the write head  3   b  is positioned in the vicinity of the objective track T y  while reading a servo pattern on the magnetic disk  2  by the read head  3   a . However, the interval between the read head  3   a  and the write head  3   b  has a deviation per product as described above. The initial position of the write head  3   b  may be positioned in the vicinity of a track different from the object track T y , and further may be positioned between tracks. 
     Next, data is written to a trial write region (S 13 ). In more detail, test data is written over one round at a position to which the write head  3   b  has moved with the objective of the track T y . In writing of data, the clock generation section  6   b  generates a read clock having the same period and phase as those of a signal read by the read head  3   a  upon passing of the write preamble  27 , and also generates a write clock having the same period as that of this read clock and having the set phase difference. 
     For example, if the phase difference is set to 0, the write clock has the same phase as that of a signal read by the read head  3   a  upon passing of the write preamble  27 . The write section  6   c  supplies test data to the write head  3   b  in synchronization with the generated write clock. Thus, information is recorded on the magnetic disk  2  in the same period as that in which the pattern of the write preamble  27  passes. 
     Next, the read head  3   a  is moved to the track T y  in the trial write region  24  to which write has been performed (S 14 ). In more detail, the read head  3   a  is positioned at the track T y  while a servo pattern is read. 
     Next, data is read (S 15 ). Data is read from the track T y  in the trial write region  24  by the read head  3   a . Data is read from all the sectors ranging from 0th sector to (P−1) th sector on the track T y . The control circuit  6   f  measures amplitudes of signals output through the read section  6   a  from the read head  3   a , and stores the representative value of the amplitude for each sector. That is, at this point, P amplitudes are stored that correspond to the second recording dots arranged in P sectors with the phase differences deviating by 360/P degrees. 
     Next, the control circuit  6   f  shifts the position of the read head  3   a  to the next track (S 16 ), and the process from step S 13  is repeated. The process from step S 13  is repeated a number of times corresponding to N tracks. This allows signal amplitude values to be obtained for the objective track and the adjoining track. 
     After repeating the process N times, the control circuit  6   f  finely shifts the position of the write head  3   b  by a distance less than the track interval, more specifically, only by 1/M of the distance between recording dots in a radius direction r (S 18 ), and then the process from step S 12  is performed again (S 19 ). Steps from S 12  to S 18  are repeated M times with the position of the write head  3   b  being finely shifted. 
     At the point when M repetitions have been completed, P signal amplitude values corresponding to 0th to (P−1) th sectors are measured N times while the position of the read head  3   a  is shifted. The N measurements are repeated M times while the position of the write head  3   b  is finely shifted. As a result, P×N×M signal amplitude values are obtained. 
     Here, the control circuit  6   f  determines optimum conditions (S 21 ). The control circuit  6   f  searches for conditions for a signal amplitude value being maximum among the stored P×N×M signal amplitude values. The signal amplitude value becomes maximum if the phase of the timing at which the write head  3   b  passes a recording dot and the phase of a write clock become the same, the shifted position in the radius direction of the write head  3   b  and any track T y  become the same, and further the read head  3   a  reads data from the track T y , The control circuit  6   f  stores the phase difference of the sector, the shift amount of the read head  3   a  and the fine shift amount of the write head  3   b  with which the maximum signal amplitude value is obtained. 
     When writing information in the information storage region  25 , the control section  6   f  corrects the phase of the write clock and the position of the write head  3   b  during writing with the stored phase difference, shift amount of the read head  3   a  and fine shift amount of the write head  3   b . In this way, the optimum access conditions to the magnetic disk are obtained. 
     In the above process, the magnetic disk makes one revolution when data is written in step S 13 , and also makes one revolution when data is read in step S 15 . As a result, the number of rotations of the magnetic disk to determine the optimum access conditions is (1+N)×M. This reduces the number of rotations of a magnetic disk for adjustment, compared with the number of rotations of (1+N)×M×L, which is needed in the case of a magnetic disk without recording dots differing from one another in phase difference as described in “BACKGROUND”. 
     Next, a second embodiment of the information storage device and the information recording medium will be described. In the following description on the second embodiment, the same elements as those in the embodiment that has been described are indicated by the same reference numerals, and description is given on the differences from the foregoing embodiment. 
       FIG. 8  illustrates the magnetic disk of a HDD being the specific second embodiment of the information storage device. 
     A half of a magnetic disk  30  is illustrated in Part (A) of  FIG. 8 , and tracks in plural portions on the magnetic disk  30  are illustrated in linear development in Parts (B) to (E) of  FIG. 8  on an enlarged scale. 
     The HDD in the second embodiment differs from the HDD in the first embodiment only in arrangement of recording dots in the trial write region of the magnetic disk and operations for determining the optimum access conditions. Therefore, only the magnetic disk is illustrated in the drawing, and other configurations are described by utilizing  FIG. 5  in the embodiment that has been described. 
     On the magnetic disk  30 , recording dots  36 B,  36 C and  36 D, following the write preambles  27 , are arranged in regular arrays on the tracks T y , T y+1 , T y+2 , . . . in the trial write region  24 . 
     However, in the magnetic disk  30  of the present embodiment, as compared with the magnetic disk  2  of the first embodiment, the phase differences of the second recording dots  36 B,  36 C and  36 D with respect to the write preambles  27  are all 0 degree, the same as the phase differences of the first recording dots  36 A in the information storage region  25 . On the other hand, the second recording dots  36 B,  36 C and  36 D of each of sectors in the trial write region  24  are arranged, on each of tracks T y , T y+1 , T y+2 , . . . , at positions deviating, from the positions in accordance with the regulation of the array of the first recording dots  36 A in the information storage region  25 , in the radius direction intersecting the circumferential direction of this array. The second recording dots  36 B,  36 C and  36 D are arranged at plural positions with deviation amounts in the radius direction that are different for each sector. In more detail, the positions of the second recording dots  36 B,  36 C and  36 D deviate towards the center by 1/P of the width between tracks, as the number of the sector in which the second recording dots are arranged increases. 
       FIG. 9  is a flow chart for explaining the process of determining the optimum access conditions to the magnetic disk illustrated in  FIG. 8 . The process from the initial value setting step (S 11 ) to the data read step (S 15 ) illustrated in  FIG. 9  are the same as those illustrated in  FIG. 7 , and therefore they are indicated by the same reference numerals. However, in the HDD having the magnetic disk  30  of the present embodiment, data is written (S 13 ) over one round of the track in the trial write region, thereby completing writing to the recording dots at positions deviating to plural extents in the radius direction. Accordingly, in operations for determining the optimum access conditions to the recording dots  36 A in the information storage region  25 , recording while finely shifting the position of the write head  3   b  (see S 18  of  FIG. 7 ) need not be repeated. Instead, regarding the HDD of the present embodiment, in the operations for determining the optimum access conditions, trial write with phase shift is performed to the second recording dots  36 B,  36 C and  36 D at positions deviating from one another in the radius direction. In more detail, for example, the write head is positioned somewhere between from T y  to T y+K , and trial write of one disk rotation is performed. This is possible even in the initial state if K is set large to some extent. Then, data is read while the read head is positioned from T y  to T y+K  in sequence. This allows the shift amount of the write head to be accurately measured from the number of the track where the maximum signal amplitude value is obtained and its sector number. Also, regarding the HDD of the present embodiment, in the operations for determining the optimum access conditions, data needs to be written plural times while the phase of the write clock is changed to search for a write clock having the optimum phase. Accordingly, for example, in the case where data is written L times while the phase of the write clock is changed in L ways to search for the optimum phase of the write clock, the time needed for the adjustment corresponds to (1+K)×L disk rotations. 
     The example where recording dots deviate in the radius direction for each sector has been described in the second embodiment. Subsequently, description will be given to the specific third embodiment, in which there are plural arrangement deviations in the radius direction of recording dots in one sector. 
     In the following description on the third embodiment, the same elements as those in the second embodiment that has been described are indicated by the same reference numerals, and description is given on the differences from the foregoing embodiments. 
       FIG. 10  illustrates a magnetic disk of a HDD being the specific third embodiment of the information storage device. 
     A half of a magnetic disk  40  is illustrated in Part (A) of  FIG. 10 , and tracks in plural portions on the magnetic disk  40  are illustrated in linear development in Part (B) of  FIG. 10  on an enlarged scale. 
     On the magnetic disk  40 , recording dots  46 B,  46 C and  46 D, following the write preambles  27 , are arranged in a regular array on the tracks T y , T y+1 , T y+2 , . . . in the trial write region  24 . In the trial write region  24 , all sectors have the same arrangement pattern such that the recording dots  46 B,  46 C and  46 D arranged in one sector deviate from one another in the radius direction.  FIG. 11  is a flow chart for explaining the process of determining the optimum access conditions to the magnetic disk illustrated in  FIG. 10 . That is, with the magnetic disk  40  of the third embodiment, after the write head is positioned at an initial position between T y  and T y+K , trial write is performed over one disk rotation while changing the write phase for each sector. Then, data is read while the read head is sequentially positioned from T y  to T y+K . In this way, the shift amount of the write head can be accurately measured and the optimum write clock phase can also be determined from the number of the track where the maximum signal amplitude value is obtained, its sector number and the position in the sector. That is, the number of disk rotations to determine the optimum access conditions is (1+K), further reducing the adjustment time. 
     Subsequently, description will be given to the fourth embodiment, where recording dots deviate both in the circumferential direction and in the radius direction. 
       FIG. 12  illustrates a magnetic disk of a HDD being the specific fourth embodiment of the information storage device. 
     A half of a magnetic disk  50  is illustrated in Part (A) of  FIG. 12 , and tracks in plural portions on the magnetic disk  50  are illustrated in linear development in Parts (B) to (E) of  FIG. 12  on an enlarged scale. 
     Recording dots  561 A,  561 B,  561 C,  562 A,  562 B,  562 C,  563 A,  563 B and  563 C in the trial write region  24  of the magnetic disk  50  illustrated in  FIG. 12  have both deviations in the circumferential direction described on the magnetic disk  2  in the first embodiment and deviations in the radius direction described on the magnetic disk  40  of the third embodiment. 
     In the trial write region  24  of the magnetic disk  50  illustrated in  FIG. 12 , the recording dots  561 A to  563 C are arranged at positions where phase differences with respect to the write preambles  27  are different for each sector. In more detail, arrangement positions of recording dots deviate by 360/P degrees as the number of the sector increases. That is, for example, the second recording dots  561 A,  561 B and  561 C in the sector  0  are arranged at a position where the phase difference with respect to the write preambles  27  is 0 degree, and the recording dots  562 A,  562 B and  562 C in the next sector  1  are arranged at a position where the phase difference with respect to the write preambles  27  is 360/P degrees. The recording dots  563 A,  563 B and  563 C in a sector “p” are arranged at a position where the phase difference with respect to the write preambles  27  is 360p/P degrees. 
     Further, in the trial write region  24 , recording dots arranged in one sector deviate from one another in the radius direction. For example, the recording dots  561 A,  561 B and  561 C in the sector  0  are arranged to deviate from one another in the radius direction. Deviation in the radius direction is the same as in other sectors in the trial write region  24 . 
     With the magnetic disk  50  of the fourth embodiment, data is written to any track in the trial write region  24 , thereby completing writing to the recording dots at positions deviating to plural extents both in the radius direction and in the circumferential direction. 
       FIG. 13  is a flow chart for explaining the process of determining the optimum access conditions to the magnetic disk illustrated in  FIG. 12 . 
     The control circuit  6  moves the write head  3   b  of the magnetic head  3  to the initial position of trial write between T y  and T y+K  (S 42 ), and writes data to the trial write region (S 43 ). By this writing, data is written to recording dots arranged at a position deviating both in the circumferential direction and in the radius direction. Then, data is read while the read head is sequentially positioned from T y  to T y+K . In this way, the shift amount of the write head can be accurately measured and the optimum write clock phase can also be determined from the number of the track where the maximum signal amplitude value is obtained, its sector number and the position in the sector. 
     In the above process, the magnetic disk makes one revolution when data is written in step S 43  and makes one revolution when data is read in step S 45 . As a result, the number of rotations of the magnetic disk to determine the optimum access conditions is (1+K). This reduces the adjustment time. There is no difference in advantage regarding the process for determining the optimum access conditions between this fourth embodiment and the third embodiment. However, in the third embodiment, a high-cost circuit that allows phase shift at a high speed needs to be provided in order to perform trial write while shifting the phase for each sector. The fourth embodiment has an advantage in device cost over the third embodiment. 
     In the foregoing description on the specific embodiments, recording dots arranged on concentric tracks are indicated as one example of the recording dots arranged in an array circumferentially in the information recording medium described in “SUMMARY”. However, the recording dots arranged in an array circumferentially may be those arranged in a spiral shape other than in a concentric shape. 
     In the foregoing description on the specific embodiments, the write preambles arranged at mutual intervals that have a ratio to the mutual intervals of the recording dots  26 A of 1:1 are indicated as one example of the magnetic pattern of the present invention. However, the magnetic pattern herein may be those recorded at mutual intervals having an integer ratio to the mutual intervals of the recording dots. For example, the mutual intervals of the array may be integer times the mutual intervals of the recording dots. 
     According to the basic embodiment of the information recording medium, second recording dots are arranged in an array circumferentially, but plural kinds of positions with different deviation amounts from the positions in accordance with the regulation appear. Therefore, information is recorded on the second recording dots along the round, thereby performing recording that complies with plural access conditions. Thus, the number of changes of access conditions can be reduced. 
     As described above, the embodiments of the information recording medium and the information storage device can reduce the adjustment time for access conditions. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.