Abstract:
An optical disk having an increased data storage capacity and accessible randomly, the positional shift of which can be quickly detected. An optical disk access device and access method are also disclosed. The optical disk ( 1 ) has a track (T 1 ) constructed of two kinds of the first sector (S 1 ) having an ID portion ( 12 ) and succeeding sectors (S 2 ) having only a sector mark portion ( 13 ), and sector marks of the tracks are different from one another. The data area is increased by compressing the ID portion, and the different marks of the tracks enable quick detection of access positional shift.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional of application Ser. No. 10/819,263, filed Apr. 7, 2004. This application is a continuation application based upon and claims the benefit of the prior PCT International Patent Application No. PCT/JP01/09306 filed on Oct. 23, 2001, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a recording medium represented by an optical disk optically rewritable, an access device and an access method. More particularly, the present invention relates to an optical disk which enables a quick random access operation if the disk is formed into a large capacity, an access device and an access method.  
         [0004]     2. Description of Related Art  
         [0005]     Conventionally, there is a recording medium provided with data identification information for each information unit of a predetermined data length in order to carry out a random access operation to data on a medium. The typical examples are such optical disks as magneto optic disk (hereinafter referred to as MO) using magneto optic recording and DVD disk (hereinafter referred to as DVD), which uses a change in phase of the medium. These optical disks are used as a large-scale external recording medium for computer. Additionally, they are used for recording visual information such as movie. As the computer has handled larger and larger data or higher-quality, longer-hour visual recording has been demanded, a further larger capacity has been demanded.  
         [0006]     An optical disk  100  based on the conventional art shown in  FIG. 9  is so constructed that information unit group constituted of plural information units are composed of tracks T 100 , which are formed of each single circle, the tracks being formed spirally. Each track T 100  is divided to sectors S 100  as information unit, which has a predetermined data length, so that data recording format is constructed. In an enlarged view of four tracks  100 A on the optical disk  100  shown in  FIG. 9 , the sector S 100  comprises data portion  120  which is a region in which data is to be written and control information portion  110 , which includes ID portion  112  as data identification information for identifying the content of the data portion  120  and a sector mark portion  111  which is recognition information for recognizing the start position of the sector S 100 .  
         [0007]      FIG. 10  shows an enlarged view of the bit structure on a boundary region of the control information portion  110  and data portion  120  on the optical disk  100 . Referring to  FIG. 10 , data is recorded on only land L 100  on the data portion  120  of the optical disk  100 . In the meantime, although not indicated, data may be recorded in only the groove G 100 . Here, each data bit pattern  125  in the data portion  120  is a rewritable data pattern, which is constructed by magneto optic recording in case of MO or phase change recording in case of DVD. Contrary to this, the sector mark portion  111  on the control information portion  110  and each control information bit pattern  115  on the ID portion  112  are uneven patterns processed in the disk  100  by etching or the like, that is, a fixed pattern constituted of so-called emboss pit pattern.  
         [0008]     As for the data bit pattern  125 , as compared to beam spot such as pick-up laser beam or the like, even if the bit pattern size or the bit pattern pitch is miniaturized, data reading corresponding to highly integration of the data bit pattern  125  is enabled by development of so-called magnetic super-resolution (MSR) technology or the like, which reads out by using temperature distribution in a beam spot.  
         [0009]     Next,  FIG. 11  shows a high-density optical disk  200  in case where the data portion  220  is formed in high density. An enlarged view of four tracks  200 A like the case of  FIG. 9  is shown here. The high-density optical disk  200  adopts a land groove recording type as shown in  FIG. 12  for integration into a higher density. The data bit pattern  125  (see  FIG. 10 ), which has conventionally been recorded in only the land L 100  or the groove G 100 , is recorded both in the land L 200  and groove G 200  by narrowing the bit pattern pitch using magnetic super-resolution (MSR) technology and the like. Thus, as compared to a case where the track T 100  is constituted of any one of the land L 100  or the groove G 100  (see  FIGS. 9, 10 ), the quantity of the tracks T 200  constituted of both the land L 200  or the groove G 200  is doubled thereby achieving high density.  
         [0010]     However, because in case of the control bit pattern  115 ,  215 , the bit pattern is formed with the emboss pit pattern at the time of manufacturing the optical disk  100  and the high density optical disk  200  as compared to the data bit patterns  125 ,  225 , processing accuracy in manufacturing process needs to be improved for miniaturization and however, the miniaturization has not been progressed. Therefore, the pitch of the track T 100  on which the data bit pattern  125  is to be recorded in the optical disk  100  is specified by the size of the emboss pit pattern of the control bit pattern  115 , so that achievement of high density cannot be attained, which is a problem to be solved.  
         [0011]     In the high-density optical disk  200  intending to achieve high density shown in  FIG. 11 , a control information portion  210  is assigned to a two-truck width consisting of two lands L 200  and two grooves G 200  and the control information portion  210  and the two-truck width are arranged in a row. That is, subsequent to a sector mark portion  211 , two ID portions  212 ,  213  are arranged in line to record. In the data portion  220 , the ID portion  212  is allocated as data identification information of the data  222  and the ID portion  213  is allocated as data identification information of the data  223 . With miniaturization of the data bit pattern  225  in the high density optical disk  200 , the overhead of the control information portion  210  in the track T 200  is increased, thereby obstructing intensification in the density of the high density optical disk  200 , which is a problem to be solved.  
         [0012]     Further, to achieve miniaturization in the emboss pit pattern of the controlling bit patterns  115 ,  215  in the control information portions  110 ,  210 , the processing accuracy in manufacturing process needs to be improved thereby inducing an increase in production cost.  
         [0013]     Further, if the size of the emboss pit pattern in the controlling bit pattern  115 ,  215  is miniaturized, it is necessary to use short wavelength laser such as blue laser as the wavelength of a pick-up laser beam, inducing an increase in part cost.  
         [0014]     To reduce the overhead of the control information portion  210  in the high-density optical disk  200 , it can be considered to adopt a method of sharing the ID portion for multiple sectors instead of the ID portions  212 ,  213  provided for each sector as the data identification information. However, in this case, if a beam spot of laser or the like suffers from a positional error generated from a normal access position, detection of normal access position is disabled or it takes an extremely long time for the detection, so that there is a fear that an access to a mistaken position may be made, which is a problem to be solved.  
       SUMMARY OF THE INVENTION  
       [0015]     An object of the present invention is to provide a recording medium, represented by an optical disk which is capable of executing secure, rapid access action while reducing the overhead of control information portion accompanying data portion of the recording medium in order to achieve higher data density of the recording medium, represented by the optical disk capable of executing random access operation, and an access device and an access method thereof.  
         [0016]     In a recording medium of the present invention for achieving the above-described object, an information unit group is composed by gathering a predetermined number of information units having data portions and control information portions. The information unit group has a set of group data identification information for discriminating data stored in each data portion as a whole. The control information portion has a recognition information for recognizing the information unit and its information differs among the information unit groups.  
         [0017]     The group data identification information is data identification information for identifying data stored in a data portion in any information unit including a head section of information units constituting an information unit group or high order identification information common to respective pieces of data identification information in the information units constituting the information unit group.  
         [0018]     This group data identification information is contained in the control information portion in a corresponding information unit of the information units constituting an information unit group.  
         [0019]     A set of the group data identification information only needs to be stored in each information unit group and the data identification information does not need to be provided on each information unit. If the group data identification information is stored in the control information portion, the overhead occupied by the control information portion on the recording medium can be reduced without reducing the size of the emboss pit pattern. Thus, high density in the recording medium can be achieved without reducing the size of the emboss pit pattern. Consequently, improvement in processing accuracy of the emboss pit pattern accompanying the high density, employment of short wavelength for the pick-up laser beam and the like become not indispensable matters thereby suppressing increases in manufacturing cost and part cost.  
         [0020]     As for the information unit group in the recording medium of the present invention, different information unit groups are formed between information unit access tracks running in parallel on the disk.  
         [0021]     The recognition information is information for detecting the head position of the information unit or contains synchronizing information used upon accessing the information unit and is repeated recursively every predetermined number of the information unit groups. The predetermined number is determined based on the positional shift expected value from a normal access position and so that an information unit groups included in the positional shift expected value is uniquely identified. The positional shift expected value is a region which may be accessed away from a normal access position when an access device makes an access.  
         [0022]     Consequently, information unit access tracks running in parallel on the recording medium are composed of different information unit groups and a different recognition information can be set for each information unit group. If it is so set that the recognition information is uniquely determined within the positional shift expected value, a positional shift of the pick-up laser beam or the like from its normal access position can be confirmed by reading the recognition information at the time of detection of the head position of each information unit or detection of the synchronizing information. The recording medium of the present invention enables the positional error to be detected rapidly.  
         [0023]     Further, if it is so set that the recognition information is repeated recursively every predetermined number of the information unit groups located within the region of the positional shift expected value, the positional shift can be confirmed by a minimum number of kinds of the recognition information.  
         [0024]     In the access device or access method of the present invention, a predetermined number of information units are gathered as a single group. As for the information unit group having a set of group data identification information, when a recording medium having a different recognition information depending on the information unit group is accessed, the recognition information of an accessed information unit group is detected by a recognition information detect and a recognition information expected value is generated successively by an expected value generator with a first detected recognition information as an initial value. Then, a detection result from the recognition information detector and a recognition information expected value from an expected value generator are compared with a comparator.  
         [0025]     At this time, a timing for scanning the information unit group upon access can be measured by the measuring unit and based on this measuring result, the expected value generator is capable of changing the recognition information expected value. Here, the measuring unit is also capable of measuring based on a reference synchronizing signal.  
         [0026]     Further, it has a recorder which stores a correspondence relation between the group data identification information and recognition information and is capable of selecting an information unit group having a recognition information supplied with a correspondence by the recorder upon access in order to detect an indicated group data identification information from the selected information unit group.  
         [0027]     Consequently, access to a recording medium having a small overhead occupied by the control information portion can be achieved while the positional error detection is being executed rapidly.  
         [0028]     The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]      FIG. 1  is a conceptual diagram showing recording format of an optical disk of the present embodiment;  
         [0030]      FIG. 2  is a circuit block diagram of an access device to an optical disk of the present embodiment;  
         [0031]      FIG. 3  is a circuit block diagram of a disk controller in the optical disk access device of the present embodiment;  
         [0032]      FIG. 4  is a circuit diagram showing comparator portion in the disk controller;  
         [0033]      FIG. 5  is a flow chart directed to a first specific example in which a predictive sector mark is set;  
         [0034]      FIG. 6  is a flow chart directed to a second specific example in which a predictive sector mark is set;  
         [0035]      FIG. 7  is a flow chart directed to a third specific example in which a predictive sector mark is set;  
         [0036]      FIG. 8  shows examples of sector mark patterns of the present embodiment;  
         [0037]      FIG. 9  is a conceptual diagram showing recording format of a conventional recoding optical disk;  
         [0038]      FIG. 10  is a conceptual diagram showing bit structure of the conventional optical disk;  
         [0039]      FIG. 11  is a conceptual diagram showing recording format of a conventional high-density optical disk;  
         [0040]      FIG. 12  is a conceptual diagram showing bit structure of the conventional high-density optical disk; and  
         [0041]      FIG. 13  shows examples of conventional sector mark patterns.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0042]     Hereinafter, the embodiment of the recording medium represented by the optical disk, access device and access method of the present invention will be described in detail with reference to  FIGS. 1-8 .  FIG. 1  shows the optical disk  1  of this embodiment. Like the high-density optical disk  200  based on the conventional art, the land groove recording type is adopted. The data portion  20  is constructed in both the land and groove so as to achieve high density. In the optical disk  1 , as shown in the enlarged view of the 4-track  1 A, each track T 1  includes two sectors, namely, a sector S 1  containing the sector mark portion  11  and the ID portion  12  in its control information portion  10  and a sector S 2  containing only sector mark portion  13 . That is, the control information portion in the sector S 2  is just the sector mark portion  13 . The sector S 1  is a first sector of the track T 1  followed by the sector S 2 . Only the first sector S 1  is provided with the ID portion  12 . Further, the same sector mark is disposed within the track T 1  for the sector mark portion  11 ,  13  in the sectors S 1 , S 2  and different sector marks are disposed among tracks. In  FIG. 1 , three kinds of the sector marks, SM 1 -SM 3  are disposed repeatedly for each track T 1 .  
         [0043]     The optical disk  1  having the above-described structure includes only the ID portion  12  for the first sector S 1  in the track T 1  containing a predetermined number of sectors as the group data identification information as compared to the conventional art of the optical disk  100  which includes the ID portion  112  as the data identification information for every sector S 100  which is an information unit for constituting the track T 100  as an information unit group and as compared to the conventional art of the high density optical disk  200  which includes the ID portions  212 ,  213  for every sector S 200  which constitutes the track T 200 . Thus, the recording region of the control information portion  10  can be reduced as compared to the conventional art without reducing the size of the emboss pit pattern, thereby making it possible to reduce the overhead by the ID portion  12 . Correspondingly, a high-density optical disk  1  which is capable of securing the data portion  20  of a larger region can be achieved. Because improvement in the processing accuracy of the emboss pit pattern and using short wavelength as the pick-up laser beam and the like become no indispensable matters with progress of higher density, increase in manufacturing cost and part cost can be blocked.  
         [0044]      FIG. 2  shows a circuit block diagram of an optical disk access device  30  which accesses to the optical disk  1  of this embodiment. A central processing unit (CPU)  31 , which acquires control program and data as required and performs access control for reading and writing data from/into the optical disk  1  is connected to a memory  32 , a disk controller  34  and a servo controller  36  through a bus  33 . Control program and data necessary for control are stored in the memory  32  and read out according to an instruction from the central processing unit (CPU)  31  as required. The central processing unit (CPU)  31  controls access operation for the optical disk  1  according to a loaded control program with reference to data appropriately. That is, a servo controller  36  is controlled to control the rotation of the optical disk  1  upon access operation. The servo controller  36  controls a motor  37  in order to control the rotation number or the like of the optical disk  1  and the like corresponding to a control from the central processing unit (CPU)  31 . On the other hand, data access is made according to an instruction to the disk controller  34 . The disk controller  34 , after receiving an instruction from the central processing unit (CPU)  31 , carries out data input/output through a read amplifier  38 R, a write amplifier  38 W and an optical disk pick-up device  39 . Data to be inputted or outputted at this time is subjected to a predetermined check for correcting positional error of access position, data error and the like through the read amplifier  38 R and the write amplifier  38 W and stored in the data memory  35 .  
         [0045]      FIG. 3  shows a block diagram of a circuit for detecting a positional error in access position in the disk controller  34  of the optical disk access device  30 . A controlling portion  51  and a register  53  for storing a positional error result are connected to a bus  33 . The controlling portion  51  is a portion for controlling data access in the disk controller  34 .  FIG. 3  indicates only a portion for detecting the positional error of the access position. An instruction is dispatched from the central processing unit (CPU)  31  or computation is made based on a sector position instructed by the central processing unit (CPU)  31  to be accessed and then, predictive sector marks SSM 1 -SSM 3  are outputted successively. A predictive sector mark signal portion  55  selects a predictive sector mark signal ( 1 - 3 ) (SSM 1 -SSM 3 ) indicating the type of outputted predictive sector marks SSM 1 -SSM 3  and activates it.  
         [0046]     On the other hand, a read sector mark signals ( 1 - 3 ) (SM 1 -SM 3 ) indicating the type of read sector marks SM 1 -SM 3  on the optical disk  1  read out by a read amplifier  38 R is selected and activated by the read sector mark signal portion  54 . A predictive sector mark signal ( 1 - 3 ) (SSM 1 -SSM 3 ) outputted from the predictive sector mark signal portion  55  of the controlling portion  51  and a read sector mark signal ( 1 - 3 ) (SM 1 -SM 3 ) outputted by a read sector mark signal portion  54  are compared by a comparator portion  52 . Here, the sector marks SM 1 -SM 3  are three kinds of marks which change repeatedly in each track T 1  as shown in  FIG. 1 .  
         [0047]     Therefore, the predictive sector mark signal ( 1 - 3 ) (SSM 1 -SSM 3 ) is selected and outputted corresponding to the predictive sector mark SSM 1 -SSM 3  indicating an access position from the predictive sector mark signal portion  55 . If comparison results accord, it indicates that access operation to the optical disk  1  is made on a sector according with an instruction from the central processing unit (CPU)  31 , indicating that so-called ON track state is attained, so that an ON track flag  53 N is set on the register  53 . If they do not accord, it indicates that the access operation to the optical disk  1  is made on a sector not according with an instruction form the central processing unit (CPU)  31 , indicating that the position of the pick-up is in OFF track state away from its proper position, so that an OFF track flag  53 F is set on the register  53 . The content of the flag stored in this register  53  is always monitored by the central processing unit (CPU)  31  through the bus  33  and the central processing unit (CPU)  31  is capable of detecting whether or not access operation to the optical disk  1  is carried out normally.  
         [0048]      FIG. 4  shows an example of the circuit in a comparator portion  52 . The comparator  52  shown in  FIG. 4  has a circuit structure necessary for an access operation to the optical disk I in which three kinds of the sector marks SM 1 -SM 3  are disposed in order repeatedly in each track T 1  as indicated for the optical disk  1  in  FIG. 1 . The comparator portion  52  is comprised of an ON track detector portion  52 N for detecting that the predictive sector mark signal ( 1 - 3 )(SSM 1 -SSM 3 ) accords with the read sector mark signal ( 1 - 3 ) (SM 1 -SM 3 ) and an OFF track detector portion  52 F for detecting that they are not accordant.  
         [0049]     The ON track detector portion  52 N includes an AND gate A 1  in which predictive sector mark signal  1  (SSM 1 ) and read sector mark signal  1 (SM 1 ) are to be inputted, an AND gate A 2  in which a predictive sector mark signal  2  (SSM 2 ) and read sector mark signal  2  (SM 2 ) are to be inputted, an AND gate A 3  in which a predictive sector mark signal  3  (SSM 3 ) and a read sector mark signal  3  (SM 3 ) are to be inputted and an OR gate O 1  in which output signals of the AND gate A 1 -A 3  are to be inputted. The individual AND gates A 1 -A 3  detect for accordance between the predictive sector mark signal ( 1 - 3 )(SSM 1 -SSM 3 ) and the read sector mark signal ( 1 - 3 ) (SM 1 -SM 3 ). If a read sector mark signal (any signal of  1 - 3 ) corresponding to a selected and activated predictive sector mark signal (any one of signals  1 - 3 ) is selected and activated, the output signal of a corresponding AND gate (any one AND gate of A 1 -A 3 ) is activated. Because the output signal from the respective AND gates A 1 -A 3  is inputted to the OR gate O 1 , the output signal from the OR gate O 1  indicates that any one of the AND gates A 1 -A 3  is activated. That is, it indicates that three kinds of the read sector marks SM 1 -SM 3  accord with the predictive sector marks SSM 1 -SSM 3 . Therefore, with an output signal from the OR gate O 1  as ON track flag signal, the ON track flag  53 N can be set in the register  53 .  
         [0050]     The OFF track detector portion  52 F has a similar structure. In the OFF track detector portion  52 F, discordance between the predictive sector mark SSM 1 -SSM 3  and the read sector mark SM 1 -SM 3  is outputted from the OR gate O 2  as the OFF track flag signal. Thus, it is provided with AND gates A 4 -A 9  for detecting discordance. A predictive sector mark signal  1 (SSM 1 ) and a read sector mark signal  2  (SM 2 ) are inputted to the AND gate A 4  in order to detect that the read sector mark signal  2  (SM 2 ) is selectively activated for the predictive sector mark signal  1  (SSM 1 ), so that discordance between the predictive and read sector marks occurs. In the same way, the AND gates A 5 -A 9  detect a discordance that the read sector mark signal  3  (SM 3 ) is detected to the predictive sector mark signal  1  (SSM 1 ), a discordance that the read sector mark signal  1  (SM 1 ) is detected to the predictive sector mark signal  2  (SSM 2 ), a discordance that the read sector mark signal  3  (SM 3 ) is detected to the predictive sector mark signal  2  (SSM 2 ), a discordance that the read sector mark signal  1  (SM 1 ) is detected to the predictive sector mark signal  3  (SSM 3 ) and a discordance that the read sector mark signal  2  (SM 2 ) is detected to the predictive sector mark signal  3  (SSM 3 ).  
         [0051]     On the optical disk  1 , the tracks T 1  are so constructed to differ between access tracks running in parallel on the disk  1 . For example, if a circumference of the disk  1  is formed as a track T 1 , different tracks T 1  are formed between adjacent access tracks running in parallel on the disk  1 . The sector marks SM 1 -SM 3  include information for detecting the head position of each of the sectors S 1 , S 2  which are information units or synchronizing information upon accessing each sector S 1 , S 2  and a different mark of them is disposed for each track T 1 . Then, this arrangement is repeated recursively every predetermined number of the tracks T 1 . That predetermined number is determined based on a positional shift expected value as a region which may be accessed with an access position deviated from its normal position. That is, they are arranged for the track T 1  included in the region of the positional shift expected value so that each different kind of the sector marks SM 1 -SM 3  is uniquely distinguished for each track T 1 .  
         [0052]     As for the optical disk  1  shown in  FIG. 1 , three kinds of the sector marks SM 1 -SM 3  are arranged recursively and repeatedly. The reason why three kinds of the sector marks are used is that as the positional shift expected value, the access position may be deflected by two tracks forward or backward with respect to a normal access position. If in such a positional shift expected value, the three kinds of the sector marks SM 1 -SM 3  are set up successively for each track, a sector mark SM 1 -SM 3  read out when the access position is deflected is always a different mark from the sector mark SSM 1 -SSM 3  expected to be read out at normal case, so that a positional error can be detected securely.  
         [0053]     If this access operation to the optical disk  1  is carried out through the optical disk access device  30  described above, an OFF track flag  53 F stored in the register  53  is detected immediately, and the access operation by the central processing unit (CPU)  31  is stopped, and the access operation is carried out again. If the optical disk  1  having the above-described structure is accessed by the optical disk access device  30  shown above, the access tracks in the sectors S 1 , S 2  arranged adjacent on the disk  1  are constituted of different tracks T 1 . Different kinds of the sector marks, SM 1 -SM 3 , which are recognition information, may be set for each track T 1 . A region in which the pick-up laser beam and the like may be deflected from the normal access position is set up as the positional shift expected value and the sector marks SM 1 -SM 3  are uniquely determined in this positional shift expected value region. Consequently, a deflection from the normal access position of the pick-up laser beam can be detected when the sector mark SM 1 -SM 3  is read out to detect the head position of each sector S 1 , S 2  or synchronizing information. Because the optical disk access device  30  stores this detection result in the register  53 , the central processing unit (CPU)  31  always monitors the content of the register  53  through the bus  33  and detects a positional shift of the access position rapidly. Then, cancellation of the access operation and repeated access operation and the like can be carried out securely and rapidly.  
         [0054]     Further, because the sector marks SM 1 -SM 3  are set up so that they are repeated recursively for every predetermined number of the tracks T 1  located within the region of the positional shift expected value and the positional shift can be recognized with a minimum number of the sector marks SM 1 -SM 3 .  
         [0055]     Next, a sequence which the controlling portion  51  of the disk controller  34  sets up by changing the predictive sector mark SSM 1 -SSM 3  successively will be described according to flow charts shown in  FIGS. 5-7  as first-third specific examples.  
         [0056]      FIG. 5  is a flow chart showing the first specific example. First, in step (hereinafter abbreviated as STEP)  1 , a specification about a target sector which should be accessed is received from the central processing unit (CPU)  31  based on the ID information (D 1 ) of all sectors on the optical disk  1  stored in the memory  32 . This specification is carried out by specifying the ID of data identification information for uniquely identifying the data portion  20  of each sector S 1 , S 2  on the optical disk  1 . The IDs stored in the ID portion of the control information portion  10  are IDs for identifying the data portion  20  in the first sector of the track T 1 .  
         [0057]     Next, whether or not the specified target sector is a first sector S 1  of the track T 1  and the sector S 1  has an ID portion is determined (STEP  2 ). Because if the ID portion exists (STEP 2 : YES), an ID corresponding to the target sector is read directly from the disk  1 , to-be-compared ID is stored with the target sector regarded as an expected sector (STEP  3 ). Unless the ID portion exists (STEP  2 : NO), the ID of the first sector S 1  is computed from an ID specified with the first sector in the track T 1  which the target sector belongs to regarded as the expected sector or by referring to a correspondence table or the like, a to-be-compared ID is stored (STEP  4 ).  
         [0058]     Reading of the disk is started after the expected sector is determined and the ID is read out from the ID portion of the first sector S 1  of each track T 1  (STEP  5 ). Then, whether or not the ID of the read sector S 1  accords the to-be-compared ID is verified (STEP  6 ). Unless they accord (STEP  6 : NO), reading of the ID portion of the first sector is continued (STEP  5 ). This action continues until they accord (STEP  6 : YES).  
         [0059]     When the ID of the first sector S 1  accords the to-be-compared ID (STEP  6 : YES), the sector mark (any mark of SM 1 -SM 3 ) of the read sector is set up as a predictive sector mark (any one of SSM 1 -SSM 3 ) (STEP  7 ). Then, to count the number of sectors to be read, a count value is added (STEP  8 ).  
         [0060]     Whether or not the count value reaches the number of sectors constituting the track T 1  is determined (STEP 9 ), and unless it reaches (STEP  9 : NO), a sector passage time of the pick-up is measured (STEP  11 ) and verification is continued by adding a count value one by one when the measurement is done (STEP  8 ). When the count value reaches the aforementioned predetermined value (STEP  9 : YES), the predictive sector mark is changed to a mark according with a next track T 1 (any mark of SSM 1 -SSM 3 ) (STEP  10 ). After that, the procedure of STEP 8 -STEP  11  is repeated corresponding to access by the central processing unit (CPU)  31  to change the predictive sector mark successively.  
         [0061]     The measurement of the sector passage time (STEP  11 ) is carried out by counting clock signals having a specific relation with the rotation number of the optical disk  1 . The change of the predictive sector mark (STEP  10 ) can be conducted by referring to a sector mark table stored preliminarily according to a standard of the optical disk  1  or if there exists regularity in data structure between the sector marks shown in  FIG. 8 , carrying out data conversion according to that regularity.  
         [0062]      FIG. 6  is a flow chart showing the sequence of the second specific example. Like step numbers are attached to the same procedure as the first specific example and then, description thereof is omitted here. In the second specific example as well as the first specific example, the first sector information (D 21 ) of each track T 1  on the optical disk  1  is stored in the memory  32 . Thus, from the central processing unit (CPU)  31 , a specification about the first sector S 1  of the track T 1  to which a target section to be accessed belongs is received based on the ID information of the sector (D 1 ) and the first sector information (D 21 ) (STEP  21 ). Then, an ID in which the first sector is specified as an expected sector is set as a to-be-compared ID (STEP  22 ).  
         [0063]     That is, determination on the position of the target sector (STEP  2 ) and the procedure for setting the to-be-compared ID based on the determination on the position (STEP  3 , STEP  4 ), which are to be conducted in case of the first specific example, become unnecessary.  
         [0064]      FIG. 7  is a flow chart showing a sequence of the third specific example. Like step numbers are attached to the same procedures as the first and second specific examples and then, description thereof is omitted. In the third specific example as well as the second specific example, the sector mark information (D 41 ) of each track T 1  is stored in the memory  32 . Specifications about the first sector S 1  of the track T 1  to which the target sector to be accessed belongs and the sector mark having that track T 1  are received from the central processing unit (CPU)  31  based on the sector ID information (D 1 ), first sector information (D 21 ) and sector mark information (D 41 ) of each track T 1 . Then, a to-be-compared ID is set up with the specified first sector as the expected sector (STEP  42 ).  
         [0065]     Next, the sector mark on the optical disk  1  is read (STEP  43 ) and the read sector mark is compared with a specified sector mark (STEP  44 ). Unless they accord (STEP  44 : NO), the track is moved and a next sector mark is read (STEP  43 ). If they accord (STEP  44 : YES), the ID portion of the first sector is read (STEP  5 ). Then, whether or not the ID of the read sector S 1  accords the to-be-compared ID is verified (STEP  6 ). Although this ID portion reading processing is the same as the first and second specific examples, the third specific example is different from the first and second specific examples in that if the comparison results discord (STEP  6 : NO), the track is moved and a next sector mark is read (STEP  43 ).  
         [0066]     Because according to the predictive sector mark setting sequence of the first-third specific examples, the predictive sector marks are set up successively, the positional shift of the access position can be detected rapidly even if the ID of each sector is not detected as a result of comparison with an actually accessed sector mark.  
         [0067]     Further because according to the second specific example, the first sector information (D 21 ) of each track T 1  on the optical disk  1  as well as the ID information (D 1 ) of all sectors on the optical disk  1  are stored in the memory  32 , the ID of the first sector of a track to which a specified target sector belongs is a preliminarily known value. Therefore, the determination on the position of the target sector (STEP  2 ) and the setting processing of the to-be-compared ID (STEP  3 , STEP  4 ) become unnecessary, the to-be-compared ID can be set up according to an instruction from the central processing unit (CPU)  31  immediately (STEP  22 ). Thus, a rapid processing can be achieved.  
         [0068]     Further, because according to the third specific example, the sector mark information (D 41 ) of each track T 1  as well as the ID information of the sector (D 1 ) and the first sector information (D 21 ) are stored in the memory  32 , the sector mark of a track to which the specified target sector belongs is a preliminarily known value. Thus, upon accessing the optical disk  1 , it is not necessary to read the ID portions of the first sectors S 1  of all the tracks T 1  and compare with the to-be-compared ID and instead, this processing needs to be carried out for only the sector mark of a specified kind. On the optical disk  1 , three kinds of the sector marks are set up in succession and the processing of reading the ID of the first sector and comparing with the to-be-compared ID only needs to be executed for ⅓ the tracks  1  on the optical disk  1 . Thus, a further rapid processing can be achieved.  
         [0069]     Next, a specific example of the mark pattern of a sector mark applicable for the present invention will be described with reference to  FIG. 8 .  FIG. 8  shows four modifications of the sector mark pattern which can be used on the optical disk  1  of the embodiment. Any example of them is a pattern modified based on odd band and even band which are conventionally used sector mark patterns shown in  FIG. 13 . The odd band sector mark pattern and even band sector mark pattern mentioned here are disposed on odd zones and even zones from the outside periphery of an optical disk of the conventional art, while multiple zones are set up on the disk, which is divided because the length of a single circumference differs depending on inside and outside of the disk, but not intended to identify the track which is mentioned in the present invention.  
         [0070]     “6T” and “12T” in  FIGS. 8, 13  indicate bit continuation time of 6-bit length and 12-bit length respectively. “0” and “1” indicate binary bit data. “No mark” and “mark” indicate absence or presence of an emboss pit pattern on the disk while “no mark” indicates a state in which no emboss pit exists and “mark” indicates a state having the emboss pit. The “no mark” and “mark” are read out as high/low level signal when they are read out as an electric signal by the optical disk access device  30 .  
         [0071]     The sector mark pattern of the example 1 shown in  FIG. 8  is generated based on the odd band sector mark pattern in  FIG. 13 . With final 6-bit pattern (“000101”) unchanged, a portion after the pattern position A in the odd band sector mark pattern is shifted to a preceding stage pattern while a portion before the pattern position A is disposed in a following stage pattern. The pattern sequence is a pattern in which the pattern sequence is changed over across the pattern position A as a boundary.  
         [0072]     The sector mark pattern of the example 2 is generated based on the even band sector mark pattern of  FIG. 13 . With a final 6-bit pattern (“000001”) unchanged, a portion after the pattern position B in the even band sector mark pattern is shifted to the previous stage pattern while a portion before the pattern position B is disposed in the following stage pattern. This is a pattern in which the pattern sequence is changed over across the pattern position B as a boundary.  
         [0073]     The sector mark pattern of the example 3 is generated based on the sector mark pattern of the example 1. With final 6-bit pattern (“000101”) unchanged, a portion after the pattern position C in the sector mark pattern of the example 1 is shifted to a previous stage pattern while a portion before the pattern position C is disposed in the following stage pattern. This is a pattern in which the pattern sequence is changed over across the pattern position C as a boundary.  
         [0074]     The sector mark pattern of the example 4 is generated based on the sector mark pattern of the example 2. With final 6-bit pattern (“000001”) unchanged, a portion after the pattern position D in the sector mark pattern of the example 2 is shifted to a previous stage pattern while a portion before the pattern position D is disposed in the following stage pattern. This is a pattern in which the pattern sequence is changed over across the pattern position D as a boundary.  
         [0075]      FIG. 8  exemplifies four kinds of the sector mark patterns as the sector mark pattern modified based on the odd/even band sector mark pattern used in the conventional art. Additionally, other kinds of the sector mark patterns can be formed by undergoing appropriate modification such as changing over the order of the pattern position.  
         [0076]     Further, a number of kinds of the sector mark patterns can be formed by adding a predetermined identification pattern to the existing odd/even band sector mark pattern or the modified pattern shown in  FIG. 8 , not by changing over the order of the pattern position of the sector mark pattern.  
         [0077]     In the meantime, the present invention is not restricted to the above-described embodiments and needless to say, the present invention may be modified in various ways within a scope not departing from the gist of the present invention.  
         [0078]     For example, although according to this embodiment, the three kinds of the sector marks SM 1 -SM 3  are set up in order to cope with a case where the positional shift expected value may be deflected by two tracks forward and backward from its normal access position, the kind of the sector mark is not restricted to this example. If the positional shift expected value is of a track, it may be set to two kinds and conversely, if the positional shift expected value is of three or more tracks, it may be set to four or more kinds. Needless to say, this can be set up appropriately depending on the standard of the optical disk, optical disk access device and access method.  
         [0079]     Although an example in which different sector marks are set up between access tracks adjacent running in parallel when the length of the track is set equal to the circumference of a disk has been described, the present invention is not restricted to this example. That is, the sector mark only needs to be uniquely set for each track within the region of the positional shift expected value including adjacent access tracks and as the length of the track, a circumference of the disk may be divided to an appropriate length. Because the circumference length differs between the inside and outside of the disk, the sections in the track occupying a single circumference of the disk may be so set as to be changeable between inside and outside. Additionally, the track sections may be set up appropriately corresponding to the characteristic of the access positional error in the optical disk, optical disk access device and the like.  
         [0080]     Although a case where the ID portion  12  is disposed in only the first sector S 1  of the track T 1 , the present invention is not restricted to this example. The ID portion does not always need to be disposed in the first sector as long as the sector constitutes the track, but the ID portion may be disposed for the ID in a sector located at an appropriate position.  
         [0081]     Although it has been described that the ID disposed in the ID portion is data identification information in a disposed sector, the present invention is not restricted to this example. The disposed ID may contain only high order identification information to be applied to identify the entire track.  
         [0082]     Although an example in which the measurement of sector passage time (STEP  11 ) is carried out by counting clock signals in a sequence for setting the predictive sector mark of the first-third specific examples has been indicated, the present invention is not restricted to this example, but ordinary measuring means may be applied. For example, it is permissible to set up to measure an actual time. The measuring processing may be carried out by any method, for example, hardware or software or cooperation of them.  
         [0083]     Although for description of the present invention, the MO and DVD are exemplified as the optical disk, any other medium may be used as long as it is a medium for executing random access operation upon data. Further, needless to say, the present invention is not restricted to the optical disk.  
         [0084]     As evident from the above description, according to the present invention, data storage capacity can be increased by compressing a region occupied by the control information portion in a recording medium which allows random access operation to a minimum, such as the optical disk without accompanying increases in manufacturing cost due to miniaturization of the medium or part cost of the access device and a positional error at an access time can be detected rapidly.