Patent Publication Number: US-8121002-B2

Title: Multi-layered information recording medium, recording apparatus, and recording method

Description:
This application is a continuation application of U.S. patent application Ser. No. 12/648,384 filed Dec. 29, 2009 now U.S. Pat. No. 7,889,610, which is a continuation of U.S. application Ser. No. 12/120,307 filed on May 14, 2008, now U.S. Pat. No. 7,663,992, which is a continuation of U.S. application Ser. No. 11/566,717 filed Dec. 5, 2006, now U.S. Pat. No. 7,715,291, which is a continuation of U.S. application Ser. No. 10/338,430 filed Jan. 8, 2003, now U.S. Pat. No. 7,184,377, the entire disclosures of which are incorporated herein by reference, and is related to sibling U.S. application Ser. Nos. 12/120,334, 12/120,323, 12/120,343 and 12/120,348 all filed on May 14, 2008, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a multi-layered information recording medium including at least two recording layers, a recording apparatus for use with the multi-layered information recording medium, and a recording method for recording information in the multi-layered information recording medium. 
     2. Description of the Related Art 
     A typical information recording medium which has a sector structure is an optical disc. In recent years, AV data, such as audio data, video data, and the like, has been digitalized, and accordingly, an optical disc having a higher recording density and larger capacity has been demanded. Providing a plurality of recording layers is useful in increasing the capacity of a disc. For example, the capacity of a read-only DVD has been increased about two times by providing two recording layers to the DVD. 
       FIG. 1  shows a structure of a typical optical disc medium  1  including a track  2  and sectors  3 . The optical disc medium  1  includes a track  2  turned multiple times in a spiral arrangement. The track  2  is divided into a large number of small sectors  3 . Regions formed on the disc medium  1  are roughly classified into a lead-in zone  4 , a user data area  8  and a lead-out zone  6 . Recording or reproduction of user data is performed on the user data area  8 . The lead-in zone  4  and the lead-out zone  6  are provided as margins such that an optical head (not shown) can appropriately follow a track even if overrunning of the optical head occurs when the optical head accesses an end portion of the user data area  8 . The lead-in zone  4  includes a disc information zone which stores parameters necessary for accessing the disc medium  1 . Physical sector numbers (hereinafter, abbreviated as “PSN(s)”) are assigned to the sectors  3  in order to identify the respective sectors  3 . Further, consecutive logical sector numbers (hereinafter, abbreviated as “LSN(s)”) which start with zero are assigned to the sectors  3  such that a superior apparatus (not shown) such as a host computer identifies the respective sectors  3 . 
       FIG. 2  illustrates a principle of reproduction of data from a read-only optical disc  30  having two recording layers. Herein, production of the read-only optical disc  30  of  FIG. 2  is briefly described. In the first place, grooves are formed on substrates  31  and  32  so as to form spiral tracks. Over the grooved surfaces of the substrates  31  and  32 , recording layers  33  and  34  are attached so as to cover the grooved surfaces. The substrates  31  and  32  are combined so as to sandwich transparent light-curable resin  35  between the recording layers  33  and  34 , thereby obtaining a single read-only optical disc  30 . In this specification, for convenience of description, in  FIG. 2 , a recording layer  34  closer to the incoming laser light  38  is referred to as a first recording layer  34 ; whereas the other recording layer  33  is referred to as a second recording layer  33 . The thickness and composition of the first recording layer  34  are calibrated such that the first recording layer  34  reflects a half of the incoming laser light  38  and transmits the other half of the incoming laser light  38 . The thickness and composition of the second recording layer  33  are calibrated such that the second recording layer  33  reflects all of the incoming laser light  38 . An objective lens  37  for gathering the laser light  38  is moved toward or away from the optical disc  30  such that the convergence point (beam spot)  36  of the laser light  38  is placed on the first recording layer  34  or the second recording layer  33 . 
       FIGS. 3A ,  3 B,  3 C and  3 D show tracks of two recording layers  41  and  42  of a read-only DVD, which are called parallel paths, and the reproduction direction and sector numbers.  FIG. 3A  shows a spiral groove pattern of the second recording layer  42 .  FIG. 3B  shows a spiral groove pattern of the first recording layer  41 .  FIG. 3C  shows the reproduction direction in user data areas  8  provided on the recording layers  41  and  42 .  FIG. 3D  shows sector numbers assigned to the recording layers  41  and  42 . 
     Now, consider the read-only DVD disc is rotated clockwise when it is viewed from the back face side of the disc in the direction along which laser light comes onto the disc, i.e., when it is viewed from the back side of the sheets of  FIGS. 3A and 3B . In this case, the laser light moves along the track  2  from the inner circumference side to the outer circumference side of the recording layers  41  and  42 . In the case where user data is sequentially reproduced along the reproduction direction shown in  FIG. 3C , reproduction is first performed from the innermost circumference position to the outermost circumference position of the user data area  8  of the first recording layer  41 . Then, reproduction is performed from the innermost circumference position to the outermost circumference position of the user data area  8  of the second recording layer  42 . The user data areas  8  of the first and second recording layers  41  and  42  are sandwiched by the lead-in zone  4  and the lead-out zone  6  such that an optical head can appropriately follow the track  2  even if overrunning of the optical head occurs. As shown in  FIG. 3D , the PSNs and LSNs of each of the recording layers  41  and  42  are incrementally assigned along the reproduction direction. The PSNs do not necessarily need to start with zero in view of convenience of disc formation. Further, the PSNs do not necessarily need to be continuously assigned between the first and second recording layers  41  and  42  (for example, a value corresponding to the layer number may be provided at the first position of each sector number). As LSNs, consecutive numbers which start with zero are assigned to all of the user data areas  8  included in the optical disc. That is, in the user data area  8  of the first recording layer  41 , the LSN at the innermost circumference position is zero, and incrementally increases toward the outermost circumference. The LSN at the innermost circumference position of the user data area  8  of the second recording layer  42  is a number obtained by adding 1 to the maximum LSN of the first recording layer  41 . The LSN of the second recording layer  42  also increases in an incremental manner toward the outermost circumference. 
       FIGS. 4A ,  4 B,  4 C and  4 D show tracks of two recording layers  43  and  44  of a read-only DVD, which is called an opposite path arrangement, and the reproduction direction and sector numbers.  FIG. 4A  shows a spiral groove pattern of the second recording layer  44 .  FIG. 4B  shows a spiral groove pattern of the first recording layer  43 .  FIG. 4C  shows the reproduction direction in user data areas  8  provided on the recording layers  43  and  44 .  FIG. 4D  shows sector numbers assigned to the recording layers  43  and  44 . 
     Now, consider the read-only DVD disc is rotated clockwise when it is viewed from the back face side of the disc in the direction along which laser light comes onto the disc, i.e., when it is viewed from the back side of the sheets of  FIGS. 4A and 4B . In this case, the laser light moves along the track  2  from the inner circumference side to the outer circumference side in the first recording layer  43 , but from the outer circumference side to the inner circumference side in the second recording layer  44 . In the case where user data is sequentially reproduced along the reproduction direction shown in  FIG. 4C , reproduction is first performed from the innermost circumference position to the outermost circumference position of the user data area  8  of the first recording layer  43 . Then, reproduction is performed from the outermost circumference position to the innermost circumference position of the user data area  8  of the second recording layer  44 . The user data area  8  of the first recording layer  43  is sandwiched by the lead-in zone  4  and a middle zone  7  such that an optical head can appropriately follow the track  2  even if overrunning of the optical head occurs. The user data area  8  of the second recording layer  44  is sandwiched by the middle zone  7  and the lead-out zone  6 . The function of the middle zone  7  is the same as that of the lead-out zone  6 . As shown in  FIG. 4D , the PSNs and LSNs of each of the recording layers  43  and  44  are incrementally assigned along the reproduction direction as in the above-described parallel paths, except that the relationship between the sector numbers and the radial direction because the spiral direction of the track  2  of the second recording layer  44  is inverse to the spiral direction of the track  2  of the first recording layer  43 . In the user data area  8  of the first recording layer  43 , the LSN is zero at the innermost circumference position, and increases incrementally toward the outer circumference side. The LSN at the outermost circumference position in the user data area  8  of the second recording layer  44  is a number obtained by adding 1 to the maximum LSN in the user data area  8  of the first recording layer  43 , and increases in an incremental manner toward the innermost circumference. 
     Above, read-only optical discs have been described. Now, features specific to a rewritable optical disc are described. Such features result from the fact that requirements on a margin for a recording operation are more severe than that for a reproduction operation. 
       FIG. 5  shows a region layout of the recording layer  45  included in a DVD-RAM which is a rewritable DVD disc. The DVD-RAM has only one recording layer (i.e., recording layer  45 ). As shown in  FIG. 5 , the lead-in zone  4  of the recording layer  45  includes a disc information zone  10 , an OPC (Optimum Power Calibration) region  11 , and a defect management region  12 . The lead-out zone  6  includes another defect management region  12 . Spare areas  13  are provided between the lead-in region  4  and the user data area  8 , and between the user data area  8  and the lead-out zone  6 , respectively. 
     The disc information zone  10  stores disc information regarding parameters necessary for recording/reproduction of data of the optical disc or data format of the optical disc. The disc information zone  10  is also included in a read-only optical disc, but the disc information zone  10  of the read-only optical disc includes nothing important other than a format identifier used for identifying the optical disc. On the other hand, in a rewritable optical disc, specific recommended values for the characteristics of the laser light used for recording, such as the laser power, pulse width, and the like, are stored for each generated mark width. The disc information zone  10  is a read-only region in which information is typically written in at the time of production of the disc. In a DVD-RAM, pits are formed in the disc surface as in a DVD-ROM. (There is a recording principle different from such a “pit” recording principle. For example, in a CD-RW, information is superposed on a meander region (called a “wobble” region) of a groove.) 
     The OPC region  11  is provided for optimally calibrating the recording power of laser light. A disc manufacturer stores recommended laser parameters for a recording operation in the disc information zone  10 . However, a laser element used by the disc manufacturer for obtaining the recommended values is different from a laser element incorporated in an optical disc drive apparatus, in respect to laser characteristics, such as the wavelength, the rising time of the laser power, and the like. Further, even a laser element of the same optical disc drive, the laser characteristics thereof vary because of a variation of the ambient temperature or deterioration which occurs over time. Thus, in an actual case, test recording is performed on the OPC region  11  while increasingly and decreasingly changing the laser parameters stored in the disc information zone  10 , such as the power value and the like, so as to obtain an optimum recording power. 
     The defect management region  12  and the spare areas  13  are provided for defect management i.e., provided for replacing a sector of the user data area  8  in which recording/reproduction cannot be appropriately performed (referred to as a “defect sector”) with another well-conditioned (i.e., sufficiently usable) sector. In a rewritable single-layer optical disc, such as a 90 mm magneto-optical disc defined in the ISO/IEC 10090 specifications, or the like, defect management is generally performed. 
     The spare areas  13  include a sector prepared as a replacement for a defect sector (referred to as a spare sector). A sector which was employed in place of a defect sector is referred to as a replacement sector. In a DVD-RAM, the spare areas  13  are placed at two positions, such that one is at the inner circumference side and the other is at the outer circumference side. The size of the spare area  13  at the outer circumference side is extendable such that an increase of defect sectors which goes beyond expectation can be handled. 
     The defect management region  12  includes: a disc definition structure (DDS)  20  having a format designed for defect management, which includes the size of the spare area  13  and the position where the spare area  13  is placed; and a defect list (DL)  21  which lists the positions of defect sectors and the positions of replacement sectors. In view of robustness, many discs are designed based on a specification such that each of the inner circumference portion and outer circumference portion of a disc has one defect management region  12 , and each defect management region  12  duplicatively stores the same content, i.e., the defect management regions  12  of the disc have the four same contents in total. Alternatively, according to the specification for a 650 MB phase change optical disc (PD), a spare area is provided in the defect management region  12 , and when a sector storing a DL  21  changes into a defect sector, the DL  21  is stored in a sector of the spare area. 
     The above structure is provided for a system including an optical disc drive in order to achieve data reliability on the same level as that of a read-only optical disc in a rewritable optical disc under a condition that margins for physical characteristics are severe in a recording operation rather than a reproduction operation. 
     Although there are read-only information recording mediums having a plurality of recording layers, all existing rewritable information recording medium have only a single recording layer. The above-described defect management for a rewritable information recording medium is directed to management of only one recording layer. There is no document which discloses defect management in an information recording medium having a plurality of recording layers. If defect management is performed independently in each recording layer, a defect sector in a certain recording layer may not be replaced even when there is no more spare area in the certain recording layer but another recording layer still has an available spare area. Further, in the case where tracks of a disc is arranged in an opposite path arrangement (see  FIGS. 4A through 4D ), if a spare area is assigned arbitrarily in each recording layer, the radial position of the first recording layer and the radial position of the second recording layer deviate from each other at a transition position where laser light transits from the first recording layer to the second recording layer. In such a case, the access speed decreases. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, there is provided a multi-layered information recording medium including a plurality of recording layers, the multi-layered information recording medium comprising: a user data area for recording user data; and a plurality of spare areas including at least one replacement region, wherein when the user data area includes at least one defect region, the at least one replacement region may be used in place of the at least one defect region, wherein the plurality of recording layers include a first recording layer and a second recording layer positioned contiguous to each other, the first recording layer includes a first user data area which is a portion of the user data area, and a first spare area which is one of the plurality of spare areas, the second recording layer includes a second user data area which is another portion of the user data area, and a second spare area which is another one of the plurality of spare areas, the first spare area is positioned so as to be contiguous to the first user data area, the second spare area is positioned so as to be contiguous to the second user data area, and the first spare area and the second spare area are positioned approximately at the same radial position on the multi-layered information recording medium. 
     In one embodiment of the present invention, logical addresses are assigned to the first user data area along a circumference direction from an inner circumference side to an outer circumference side of the multi-layered information recording medium; logical addresses are assigned to the second user data area along a circumference direction from the outer circumference side to the inner circumference side of the multi-layered information recording medium; the logical addresses assigned to the first user data area and the logical addresses assigned to the second user data area are in series; the first spare area is positioned so as to be contiguous to a sector to which a maximum logical address is assigned among a plurality of sectors included in the first user data area; and the second spare area is positioned so as to be contiguous to a sector to which a minimum logical address is assigned among a plurality of sectors included in the second user data area. 
     According to another aspect of the present invention, there is provided a multi-layered information recording medium including a plurality of recording layers, the multi-layered information recording medium includes: a user data area for recording user data; and a plurality of OPC regions provided for calibrating a recording power of laser light, wherein each of the plurality of recording layers includes a corresponding one of the plurality of OPC regions. 
     In one embodiment of the present invention, the multi-layered information recording medium further comprises a calibration result storage region for storing a result of calibration of the recording power of the laser light, wherein the calibration result storage region is provided in at least a reference layer selected from the plurality of recording layers. 
     In another embodiment of the present invention, the plurality of recording layers include a first recording layer and a second recording layer positioned contiguous to each other; the first recording layer includes a first user data area which is a portion of the user data area; the second recording layer includes a second user data area which is another portion of the user data area; logical addresses are assigned to the first user data area along a circumference direction from an inner circumference side to an outer circumference side of the multi-layered information recording medium; and logical addresses are assigned to the second user data area along a circumference direction from the outer circumference side to the inner circumference side of the multi-layered information recording medium. 
     In still another embodiment of the present invention, the plurality of recording layers include a first recording layer and a second recording layer positioned contiguous to each other; the first recording layer includes a first user data area which is a portion of the user data area; the second recording layer includes a second user data area which is another portion of the user data area; logical addresses are assigned to the first user data area along a circumference direction from an inner circumference side to an outer circumference side of the multi-layered information recording medium; and logical addresses are assigned to the second user data area along a circumference direction from the inner circumference side to the outer circumference side of the multi-layered information recording medium. 
     According to still another aspect of the present invention, there is provided a multi-layered information recording medium including a plurality of recording layers, the multi-layered information recording medium comprising: a user data area for recording user data; and at least one spare area including at least one replacement region, wherein when the user data area includes at least one defect region, the at least one replacement region may be used in replacement of the at least one defect region, wherein the user data area includes a plurality of sectors, a logical address is assigned to each of the plurality of sectors, and one of the at least one spare area is positioned so as to be contiguous to a sector to which a maximum logical address is assigned among the plurality of sectors included in the user data area, and said spare area is expandable. 
     In one embodiment of the present invention, the spare area positioned contiguous to the sector to which the maximum logical address is assigned is expandable in a direction from the spare area toward the user data area. 
     In another embodiment of the present invention, the plurality of recording layers include a first recording layer and a second recording layer positioned contiguous to each other; the first recording layer includes a first user data area which is a portion of the user data area; the second recording layer includes a second user data area which is another portion of the user data area; logical addresses are assigned to the first user data area along a circumference direction from an inner circumference side to an outer circumference side of the multi-layered information recording medium; and logical addresses are assigned to the second user data area along a circumference direction from the outer circumference side to the inner circumference side of the multi-layered information recording medium. 
     In still another embodiment of the present invention, the plurality of recording layers include a first recording layer and a second recording layer positioned contiguous to each other; the first recording layer includes a first user data area which is a portion of the user data area; the second recording layer includes a second user data area which is another portion of the user data area; logical addresses are assigned to the first user data area along a circumference direction from an inner circumference side to an outer circumference side of the multi-layered information recording medium; and logical addresses are assigned to the second user data area along a circumference direction from the inner circumference side to the outer circumference side of the multi-layered information recording medium. 
     According to still another aspect of the present invention, there is provided a recording apparatus for recording information in a multi-layered information recording medium including a plurality of recording layers, wherein: the multi-layered information recording medium includes a user data area for recording user data, and a plurality of spare areas including at least one replacement region, wherein when the user data area includes at least one defect region, the at least one replacement region may be used in place of the at least one defect region, wherein the plurality of spare areas are provided in at least two recording layers of the plurality of recording layers; the recording apparatus includes an optical head section capable of optically writing the information in the multi-layered information recording medium from one surface of the multi-layered information recording medium, and a control section for controlling execution of a defect management process using the optical head section; and the defect management process includes steps of finding at least one available spare area among the plurality of spare areas, determining whether or not the user data area includes a defect region, if it is determined that the user data area includes a defect region, selecting a spare area whose distance from the defect region is shortest among the at least one spare area found, and replacing the defect region with a replacement region included in the selected spare area. 
     According to still another aspect of the present invention, there is provided a recording apparatus for recording information in a multi-layered information recording medium including a plurality of recording layers, wherein: the multi-layered information recording medium includes a user data area for recording user data, and a plurality of spare areas including at least one replacement region, wherein when the user data area includes at least one defect region, the at least one replacement region may be used in place of the at least one defect region, wherein the plurality of spare areas are provided in at least two recording layers of the plurality of recording layers, and each of the plurality of recording layers includes a portion of the user data area; the recording apparatus includes an optical head section capable of optically writing the information in the multi-layered information recording medium from one surface of the multi-layered information recording medium, and a control section for controlling execution of a defect management process using the optical head section; and the defect management process includes steps of finding at least one available spare area among the plurality of spare areas, determining whether or not the user data area includes a defect region, if it is determined that the user data area includes a defect region, determining whether or not a recording layer, in which an area including the defect region which is a portion of the user data area exists, includes at least one of the at least one spare area found, if it is determined that the recording layer, in which the area including the defect region exists, includes none of the at least one spare area found, selecting a spare area whose distance from the defect region is shortest among the at least one spare area found, and replacing the defect region with a replacement region included in the selected spare area. 
     According to still another aspect of the present invention, there is provided a recording method for recording information in a multi-layered information recording medium including a plurality of recording layers, wherein: the multi-layered information recording medium includes a user data area for recording user data, and a plurality of spare areas including at least one replacement region, wherein when the user data area includes at least one defect region, the at least one replacement region may be used in place of the at least one defect region, wherein the plurality of spare areas are provided in at least two recording layers of the plurality of recording layers; and the recording method includes steps of finding at least one available spare area among the plurality of spare areas, determining whether or not the user data area includes a defect region, if it is determined that the user data area includes a defect region, selecting a spare area whose distance from the defect region is shortest among the at least one spare area found, and replacing the defect region with a replacement region included in the selected spare area. 
     According to still another aspect of the present invention, there is provided a recording method for recording information in a multi-layered information recording medium including a plurality of recording layers, wherein: the multi-layered information recording medium includes a user data area for recording user data, and a plurality of spare areas including at least one replacement region, wherein when the user data area includes at least one defect region, the at least one replacement region may be used in place of the at least one defect region, wherein the plurality of spare areas are provided in at least two recording layers of the plurality of recording layers, and each of the plurality of recording layers includes a portion of the user data area; and the recording method includes steps of finding at least one available spare area among the plurality of spare areas, determining whether or not the user data area includes a defect region, if it is determined that the user data area includes a defect region, determining whether or not a recording layer, in which an area including the defect region which is a portion of the user data area exists, includes at least one of the at least one spare area found, if it is determined that the recording layer, in which the area including the defect region exists, includes none of the at least one spare area found, selecting a spare area whose distance from the defect region is shortest among the at least one spare area found, and replacing the defect region with a replacement region included in the selected spare area. 
     Thus, the invention described herein makes possible the advantages of providing: (1) a multi-layered information recording medium wherein placement of spare areas in a plurality of recording layers is designed such that the spare areas are used efficiently and access characteristics are improved; and (2) an information recording method, an information reproduction method, an information recording apparatus and an information reproduction apparatus for use with the above multi-layered information recording medium. 
     These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a structure of a track and sectors in a commonly employed optical disc. 
         FIG. 2  illustrates a reproduction principle for an optical disc having two recording layers. 
         FIG. 3A  shows a groove pattern in a second recording layer in a parallel path of a DVD disc. 
         FIG. 3B  shows a groove pattern in a first recording layer in a parallel path of a DVD disc. 
         FIG. 3C  illustrates a recording/reproduction direction in a parallel path of a DVD disc. 
         FIG. 3D  illustrates assignment of sector numbers in a parallel path of a DVD disc. 
         FIG. 4A  shows a groove pattern in a second recording layer in an opposite path of a DVD disc. 
         FIG. 4B  shows a groove pattern in a first recording layer in an opposite path of a DVD disc. 
         FIG. 4C  illustrates a recording/reproduction direction in an opposite path of a DVD disc. 
         FIG. 4D  illustrates assignment of sector numbers in an opposite path of a DVD disc. 
         FIG. 5  shows a region layout in a DVD-RAM. 
         FIG. 6  shows a region layout in a multi-layered information recording medium according to embodiment 1 of the present invention. 
         FIG. 7  shows a data structure of a DDS  20  according to embodiment 1 of the present invention. 
         FIG. 8  shows a spare full flag group  208  according to embodiment 1 of the present invention. 
         FIG. 9  shows a data structure of a DL  21  according to embodiment 1 of the present invention. 
         FIG. 10  illustrates assignment of sector numbers in embodiment 1 of the present invention. 
         FIG. 11A  shows a layout of a recording layer included in an information recording medium having a single recording layer. 
         FIG. 11B  shows a layout of recording layers included in a multi-layered information recording medium according to embodiment 2 of the present invention. 
         FIG. 11C  shows a variation of the layout of recording layers shown in  FIG. 11B . 
         FIG. 12  shows a region layout of a multi-layered information recording medium according to embodiment 2 of the present invention. 
         FIG. 13  shows a data structure of a DDS  20  according to embodiment 2 of the present invention. 
         FIG. 14  shows a spare full flag group  208  according to embodiment 2 of the present invention. 
         FIG. 15  illustrates assignment of sector numbers in embodiment 2 of the present invention. 
         FIG. 16  shows a region layout of a multi-layered information recording medium according to embodiment 3 of the present invention. 
         FIG. 17  illustrates assignment of sector numbers in embodiment 3 of the present invention. 
         FIG. 18  shows an information recording/reproducing apparatus  500  according to embodiment 4 of the present invention. 
         FIG. 19  is a flowchart for illustrating a procedure of obtaining defect management information according to embodiment 4 of the present invention. 
         FIG. 20  is a flowchart for illustrating a reproduction procedure of sectors according to embodiment 4 of the present invention, wherein replacement is considered. 
         FIG. 21  is a flowchart for illustrating a procedure of converting LSNs to PSNs according to embodiment 4 of the present invention. 
         FIG. 22  is a flowchart for illustrating a procedure of updating defect management information according to embodiment 4 of the present invention. 
         FIG. 23  is a flowchart for illustrating a recording procedure in sectors according to embodiment 4 of the present invention, wherein replacement is considered. 
         FIG. 24A  is a flowchart for illustrating an assignment procedure of replacement sectors according to embodiment 4 of the present invention. 
         FIG. 24B  shows a variation of the flowchart shown in  FIG. 24A . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
     Hereinafter, a multi-layered information recording medium according to embodiment 1 of the present invention is described with reference to the drawings. In the present invention, the multi-layered information recording medium refers to an information recording medium including two or more recording layers. 
       FIG. 6  shows a region layout of a multi-layered information recording medium  50  according to embodiment 1 of the present invention. The multi-layered information recording medium  50  includes two recording layers  51  and  52 . The multi-layered information recording medium  50  includes a user data area  5  for recording user data. In this embodiment of the present invention, the upper recording layer shown in  FIG. 6  is referred to as a first recording layer, and the lower recording layer is referred to as a second recording layer. The first recording layer  51  includes, from the inner circumference side to the outer circumference side along the recording/reproduction direction, a lead-in zone  101 , a head spare area  105 , a first user data area  15 , which is a portion of the user data area  5 , an intermediate spare area  106 , and a middle region  102 . The second recording layer  52  includes, from the outer circumference side to the inner circumference side along the recording/reproduction direction, a middle region  103 , an intermediate spare area  106 ′, a second user data area  16 , which is a portion of the user data area  5 , an end spare area  107 , and a lead-out zone  104 . 
     Each of the head spare area  105 , the intermediate spare area  106 , the intermediate spare area  106 ′, and the end spare area  107  includes at least one replacement region (which is a “spare sector” in the embodiments of the present invention). When the user data area  5  has at least one defect region (which is a “defect sector” in the embodiments of the present invention), the spare sector can be used in place of the defect sector. 
     The lead-in zone  101  includes a disc information zone  10 , an OPC region  11 , and a defect management region  12 . The defect management region  12  is included in the middle region  102 . The OPC region  11  is included in the lead-out zone  104 . The defect management region  12  includes a DDS  20  and DL  21 . 
     The disc information zone  10  is provided in the first recording layer  51 . The disc information zone  10  includes recording/reproduction parameters which are recommended for both the first and second recording layers  51  and  52 . With such a structure, the parameters for all the recording layers  51  and  52  of the multi-layered information recording medium  50  can be obtained by simply accessing the first recording layer  51 . Thus, the processing speed can be advantageously increased. 
     The defect management region  12  is provided in the first recording layer  51 . The defect management region  12  includes defect management information about defect management for both the first and second recording layers  51  and  52 . That is, the DDS  20  describes information about the head spare area  105 , the intermediate spare area  106 , and the end spare area  107 . Further, the DL  21  lists the positions of defect sectors and the positions of replacement sectors which are provided for use in place of the defect sectors for both the first and second recording layers  51  and  52 . With such a structure, all of the information about defect management of the multi-layered information recording medium  50  can be obtained by simply accessing the first recording layer  51 . Thus, the processing speed can be advantageously increased. 
     The head spare area  105  and the intermediate spare area  106  are placed contiguous to the both ends of the user data area  15 . The intermediate spare area  106 ′ and the end spare area  107  are placed contiguous to the both ends of the user data area  16 . This arrangement has an advantage such that a sequential recording/reproduction operation along the recording/reproduction direction can be performed at a high speed as compared with a case where the spare areas  105  to  107  are placed such that the spare areas divide the user data area  15  or  16  at an intermediate portion. Further, the intermediate spare area  106  and the intermediate spare area  106 ′ are placed at the same radial position in the multi-layered information recording medium  50 . With this arrangement, when the focal position of laser light transits from the user data area  15  of the first recording layer  51  to the user data area  16  of the second recording layer  52 , the moving distance of the optical head along the radial direction is ideally zero (0), and therefore, a higher accessing speed can be achieved. Herein, the moving distance is ideally zero, i.e., may not be zero, because a deviation may occur when the first recording layer  51  and the second recording layer  52  are combined, or the focal position of laser light deviates to an amount corresponding to the eccentricity of the disc during the switching of the focal position of the laser light, and in such a case, a slight movement of the laser light along the radial direction is necessary. 
     The OPC region  11  provided for calibrating the recording power of the laser light is provided in both the first recording layer  51  and the second recording layer  52 . This is because one of the recording layers is translucent, whereas the thickness of the other recording layer is calibrated so as to reflect all of the laser light, and accordingly, the recording characteristics are different for each recoding layer. Thus, the OPC region  11  is provided in each of the first recording layer  51  and the second recording layer  52  so that calibration of the recording power of the laser light can be performed independently in each recording layer. 
     It is desirable that storage regions for control information other than the disc information zone  10  and the defect management region  12 , such as a calibration result storage region  14  for storing the calibration result for the recording power of the laser light, are provided in the first recording layer  51  in view of the processing speed as described above. 
     Each of the sizes of the head spare area  105 , the intermediate spare area  106 , and the end spare area  107  may be zero. For example, in the case where the sizes of the head spare area  105  and the intermediate spare area  106  are not zero, and the size of the end spare area  107  is zero, the above described advantages of the present invention can be achieved. 
       FIG. 7  shows the data structure of the DDS  20  according to embodiment 1 of the present invention. The data of the DDS  20  includes a DDS identifier  201 , a LSN 0  position  202 , a head spare area size  203 , and an intermediate spare area  203 , an intermediated spare area size  204 , an end spare area size  205 , a first-layer end LSN  206 , a second-layer end LSN  207 , and a spare full flag group  208 . The DDS identifier  201  indicates that this data structure is DDS. The LSN 0  position  202  represents the PSN (i.e., physical address) of a sector whose LSN (i.e., logical address) is 0. The head spare area size  203  represents the number of sectors in the head spare area  105 . The intermediate spare area size  204  represents the number of sectors in the intermediate spare area  106 . The end spare area size  205  represents the number of sectors in the end spare area  107 . The first-layer end LSN  206  represents the LSN assigned to the last sector in the user data area  15  of the first recording layer  51 . The first-layer end LSN  206  is identical to the number of sectors in the user data area  15 . The second-layer end LSN  207  represents the LSN assigned to the last sector in the user data area  16  of the second recording layer  52 . The second-layer end LSN  207  is equal to a value obtained by adding the number of sectors in the user data area  15  to the number of sectors in the user data area  16 . The spare full flag group  208  is a group of flags which represent whether or not there is an available spare sector in the spare areas  105  to  107 . 
       FIG. 8  shows an example of the spare full flag group  208 . Ahead spare area full flag  221  corresponds to the head spare area  105 . A first-layer intermediate spare area full flag  222  corresponds to the intermediate spare area  106 . A second-layer intermediate spare area full flag  223  corresponds to the intermediate spare area  106 ′. A second-layer end spare area full flag  224  corresponds to the end spare area  107 . The present invention is not limited to this flag arrangement so long as the spare full flag group  208  includes flags corresponding to the spare areas  105  to  107 . 
       FIG. 9  shows the data structure of the DL  21  according to embodiment 1 of the present invention. The data of the DL  21  includes a DL identifier  301 , a DL entry number  302 , and 0 (zero) or more DL entries  303 . The DL identifier  301  indicates that this data structure is DL. The DL entry number  302  represents the number of DL entries  303 . The DL entries  303  each include information about a defect sector position  304  and a replacement sector position  305 . The PSN of a defect sector is stored as the defect sector position  304 . As the replacement sector position  305 , the PSN of a replacement sector is stored. The PSN includes a layer number  306  and an intralayer sector number  307 . The layer number  306  may be any value so long as the layer can be identified by the value. For example, the layer number  306  of the first recording layer  51  is 0, and the layer number  306  of the second recording layer  52  is 1. The intralayer sector number  307  may be any value so long as sectors in a certain recording layer can be identified by the value. For example, the intralayer sector number  307  incrementally increases by one every time one sector is passed along the recording/reproduction direction. Even if the relationship between the PSN of a sector in the first recording layer  51  and the PSN of a sector in the second recording layer  52  placed at the same radial position is two&#39;s complement, the above-described conditions are satisfied as in the opposite paths of a DVD-ROM. For example, consider that the PSN is represented in the 28-bit format, and the PSN of the first recording layer  51  is within the range of 0000000h to 0FFFFFFh (“h” means that the value is represented by a hexadecimal number). When the PSN of a certain sector in the first recording layer  51  is 0123450h, the PSN of a corresponding sector in the second recording layer  52  at the same radial position is FEDCBAFh (see the following steps 1) to 4)): 
                                                                1)   0   1   2   3   4   5   0   : hexadecimal                                        number       2)   0000   0001   0010   0011   0100   0101   0000   : binary number       3)   1111   1110   1101   1100   1011   1010   1111   : bit-inverted                                        binary number       4)   F   E   D   C   B   A   F   : hexadecimal                                        number                    
The most significant bit of the PSN of the first recording layer  51  is always zero, and the most significant bit of the PSN of the second recording layer  52  is always F. This most significant bit is equal to the layer number  306 . In the first recording layer  51 , when the track is followed along the recording/reproduction direction (from the inner circumference side to the outer circumference side), the PSN of the next sector is 0123451h. In the second recording layer  52 , when the track is followed along the recording/reproduction direction (from the outer circumference side to the inner circumference side), the PSN of the next sector is FEDCBB0h. The sector number  307  can be obtained by simply removing the most significant bit (i.e., the layer number  306 ) from the PSN. In the first recording layer  51 , the sector number  307  of a current sector is 123450h, and the sector number  307  of a next sector is 123451h. In the second recording layer  52 , the sector number  307  of a current sector is EDCBAFh, and the sector number  307  of a next sector is EDCBB0h.
 
     When the DL  21  of the present invention is used, a defect sector can be replaced with a spare sector in a spare area provided in the same recording layer in which the defect sector is included, and moreover, a defect sector can be replaced with a spare sector of a recording layer different from the recording layer in which the defect sector is included. For example, a DL entry  303  wherein the defect sector position  304  represents the PSN in the first recording layer  51 , and the replacement sector position  305  represents the PSN in the second recording layer  52 , means that a defect sector in the first user data area  15  of the first recording layer  51  was replaced with a spare sector in the second recording layer  52 . If a defect list is formed by DL entries based on which a recording layer cannot be identified, as in the conventional art, replacement processing cannot be successfully performed when the number of defect sectors is greater than the number of spare sectors provided in a recording layer. Thus, according to embodiment 1 of the present invention, defect sectors can be replaced with spare sectors until all the spare sectors of all the recording layers are used. That is, the spare areas can be efficiently used. 
       FIG. 10  illustrates the assignment of the sector numbers according to embodiment 1 of the present invention. The sector numbers assigned from the inner circumference to the outer circumference in the first recording layer  51  and then from the outer circumference to the inner circumference in the second recording layer  52  are arranged horizontally from left to right in the drawing. Thus, from left to right in the drawing, the head spare area  105 , the first user data area  15 , the intermediate spare area  106 , the intermediate spare area  106 ′, the second user data area  16 , and the end spare area  107  occur in this order. Each of these regions and areas include a plurality of sectors. In the first recording layer  51 , the PSN increases by 1 every time a single sector is passed toward the outer circumference side; whereas in the second recording layer  52 , the PSN increases by 1 every time a single sector is passed toward the inner circumference side. The assignment may be made such that values obtained by removing the layer number (i.e., the most significant bit) from the PSNs of the first recording layer  51  are in the same numeric range as values obtained by removing the layer number (i.e., the most significant bit) from the PSNs of the second recording layer  52 . (That is, the minimum PSN within the sectors included in the head spare area  105  of the first recording layer  51  is identical to the minimum PSN within the sectors included in the intermediate spare area  106 ′ of the second recording layer  52  except for the layer number; and the maximum PSN within the sectors included in the intermediate spare area  106  of the first recording layer  51  is identical to the maximum PSN within the sectors included in the end spare area  107  of the second recording layer  52  except for the layer number.) The relationship of the PSN of a sector in the first recording layer  51  and the PSN of a sector in the second recording layer  52  placed at the same radial position may be two&#39;s complement as in the opposite paths of a DVD-ROM. 
     The LSNs are assigned only to a plurality of sectors included in the user data area  5 . In the first user data area  15 , the LSNs are assigned along the circumference direction of the multi-layered information recording medium  50 . In the second user data area  16  also, the LSNs are assigned along the circumference direction of the multi-layered information recording medium  50 . The LSNs assigned to the first user data area  15  and the LSNs assigned to the second user data area  16  are consecutive numbers. 
     In the first user data area  15  of the first recording layer  51 , 0 (zero) is assigned to a sector at the innermost circumference position as a LSN. The LSN incrementally increases by 1 every time one sector is passed from the inner circumference side to the outer circumference side. In the second user data area  16  of the second recording layer  52 , a value obtained by adding 1 to the maximum LSN within the first user data area  15  of the first recording layer  51  is assigned to a sector at the outermost circumference position as a LSN. The LSN incrementally increases by 1 every time one sector is passed from the outer circumference side to the inner circumference side. In this way, in the second user data area  16 , the logical addresses (i.e., LSNs) are assigned along a direction opposite to the assignment direction in the first user data area  15 . 
     The intermediate spare area  106  is positioned contiguous to a sector having the maximum logical address (i.e., maximum LSNs) in the first user data area  15 . The intermediate spare area  106 ′ is positioned contiguous to a sector having the minimum logical address (i.e., minimum LSNs) in the second user data area  16 . As described above, the intermediate spare area  106  and the intermediate spare area  106 ′ are placed at the same radial position of the multi-layered information recording medium  50 . Accordingly, the sector having the maximum logical address in the first user data area  15  and the sector having the minimum logical address in the second user data area  16  are at the same radial position of the multi-layered information recording medium  50 . Due to this arrangement, the moving distance of laser light along the radial direction is ideally zero when the focal position of the laser light is switched from the sector having the maximum logical address in the first user data area  15  to the sector having the minimum logical address in the second user data area  16 . 
     Even if user data has already been recorded in the user data area  5 , the size of the spare areas can be increased. This is explained with reference to  FIG. 10 . The end spare area  107  is placed contiguous to a sector having the maximum LSN in the user data area  5 . The end spare area  107  can be expanded in a direction from the end spare area  107  toward the second user data area  16  (i.e., the direction indicated by arrow  107 ′ in  FIG. 10 ). 
     First, before the end spare area  107  is expanded in the direction indicated by arrow  107 ′, user data recorded in a portion of the second user data area  16  which will be converted to the end spare area  107  is transferred to another portion of the user data area  5 . Then, the file management information of the transferred user data is modified such that the file management information of the transferred user data (which is one of the information managed by a file system) refers to a sector position to which the user data has been transferred. Next, change of the size of the user data area  5  is reflected in the volume space management information (which is one of the information managed by a file system). Then, in the last step, the size of the end spare area  107  is increased. It should be noted that increasing the sizes of the head spare area  105  and the intermediate spare areas  106  and  106 ′ is not practical because, if the sizes of these regions are increased, the assignment of the LSNs to the user data area  5  are changed, and as a result, the file system for managing the user data area  5  using the LSNs would corrupt. 
     As described above, according to embodiment 1 of the present invention, in a multi-layered information recording medium having two recording layers, continuous accessibility can be improved. Furthermore, a defect sector can be replaced with a spare area in any recording layer, and therefore, the spare areas can be efficiently used. Furthermore, the size of the spare area can be increased so as to prevent lack of spare areas, whereby reliability of data can be improved. 
     Embodiment 2 
     Hereinafter, a multi-layered information recording medium according to embodiment 2 of the present invention is described with reference to the drawings. 
     First, a reference layer which is used as a reference among a plurality of recording layers included in a multi-layered information recording medium is described.  FIGS. 11A ,  11 B and  11 C illustrate a layout of recording layers of an information recording medium according to embodiment 2.  FIG. 11A  illustrates a layout of layers included in an information recording medium  53  having a single recording layer  402 . In  FIG. 11A , the information recording medium  53  includes a transparent resin  401 , a total reflection recording layer  402 , and a substrate  400  along a direction through which laser light enters the information recording medium  53 . The total reflection recording layer  402  is positioned at depth d from the surface of the transparent resin  401  through which the laser light enters.  FIGS. 11B and 11C  illustrate layouts of the layers included in information recording mediums  54  and  55  each of which has three recording layers  402 ,  403  and  404 . In these layouts, the translucent recording layers  403  and  404  are provided in this order, toward coming laser light, on the total reflection recording layer  402  which is formed on the substrate  400 , such that the translucent recording layers  403  and  404  are sandwiched by the transparent resin  401 . In the information recording medium  54  of  FIG. 11B , the total reflection recording layer  402  is at depth d from the surface of the outermost transparent resin layer  401  through which the laser light enters the information recording medium  54 . In the information recording medium  55  of  FIG. 11C , the translucent recording layer  403  is at depth d from the surface of the outermost transparent resin layer  401  through which the laser light enters the information recording medium  55 . This is a typical difference between the information recording medium  54  and the information recording medium  55 . 
     In general, an optical head section is designed such that an optimum light spot is obtained at depth d. Herein, a recording layer at depth d is referred to as a reference layer for convenience of explanation. Regions where important information is to be stored, for example, a disc information zone  10  and a defect management region  12 , are desirably positioned in the reference layer. In  FIG. 6 , the first recording layer  51 , in which the disc information zone  10 , the defect management region  12 , and the calibration result storage region  14  are positioned, is a reference layer. 
     In the description below, the recording layers are referred to as a first recording layer, a second recording layer, a third recording layer, . . . , in the order of largeness of the LSN from the minimum LSN. For example, in the information recording medium  54  shown in  FIG. 11B , the total reflection recording layer  402  is referred to as the first recording layer, the translucent recording layer  403  is referred to as the second recording layer, and the translucent recording layer  404  is referred to as the third recording layer. Further, for example, in the information recording medium  55  illustrated in  FIG. 11C , the translucent recording layer  403  is referred to as the first recording layer, the translucent recording layer  404  is referred to as the second recording layer, and the total reflection recording layer  402  is referred to as the third recording layer. Thus, the numbering for recording layers does not necessarily depend on the positional relationship of the recording layers. In the above explanation, examples having three recording layers have been described. However, the above explanation similarly applies to any information recording medium including two or more recording layers. 
       FIG. 12  illustrates a region layout of a multi-layered information recording medium  56  according to embodiment 2 of the present invention. The multi-layered information recording medium  56  includes three recording layers  57 ,  58  and  59 . The multi-layered information recording medium  56  includes a user data area  5  for recording user data. The first recording layer  57  includes a lead-in zone  101 , a head spare area  105 , a first user data area  17  which is a portion of the user data area  5 , an intermediate spare area  106 , and a middle region  102 , from the inner circumference side to the outer circumference side, which is the same direction as the recording/reproduction direction. The second recording layer  58  includes a middle region  103 , an intermediate spare area  106 ′, a second user data area  18  which is a portion of the user data area  5 , an intermediate spare area  108 , and a middle region  109 , from the outer circumference side to the inner circumference side, which is the same direction as the recording/reproduction direction. The third recording layer  59  includes a middle region  109 , an intermediate spare area  108 ′, a third user data area  19  which is a portion of the user data area  5 , an end spare area  107 , and a lead-out zone  104 , from the inner circumference side to the outer circumference side, which is the same direction as the recording/reproduction direction. The lead-in zone  101  includes a disc information zone  10 , an OPC region  11  and a defect management region  12 . The middle region  102  includes a defect management region  12 . The middle region  109  includes an OPC region  11 . The defect management region  12  includes a DDS  20  and a DL  21 . 
     The disc information zone  10  is provided in the first recording layer  57 . The disc information zone  10  stores recording/reproduction parameters, which are recommended for each of all the recording layers  57 ,  58  and  59 . With such an arrangement, parameters for all the recording layers  57 ,  58  and  59  of the multi-layered information recording medium  56  can be obtained by simply accessing the first recording layer  57 , and thus, the processing speed can be advantageously increased. 
     The defect management region  12  is provided in the first recording layer  57 , and includes defect management information for defect management in all the recording layers  57 ,  58  and  59 . That is, the DDS  20  describes a head spare area  105 , intermediate spare areas  106 ,  106 ′,  108  and  108 ′, and information about the end spare area  107 . The DL  21  lists the positions of defect sectors in all of the recording layers  57 ,  58  and  59 , and the positions of replacement sectors which are used in place of the defect sectors. With such an arrangement, all information about defect management of the multi-layered information recording medium  56  can be obtained by simply accessing the first recording layer  57 , and thus, the processing speed can be advantageously increased. 
     Each of the spare areas  105  to  108 ′ of the recording layers  57  to  59  is provided at the position contiguous to either end portion of the first to third user data areas  17  to  19 . This arrangement is advantageous because sequential recording/reproduction along the recording/reproduction direction can be performed at a high speed, as compared with a case where a spare area is provided at a position such that any of the first to third user data areas  17  to  19  is interrupted by the spare area. Further, the intermediate spare areas  106  and  106 ′ are provided at the same radial position in an area of the outer circumference side of the recording layers  57  and  58 . With such an arrangement, the moving distance of an optical head section along the radial direction is ideally zero when the focal position of the laser light is switched from the first user data area  17  to the second user data area  18 . Thus, accessing at a higher speed can be realized. Further, the intermediate spare areas  108  and  108 ′ are provided at the same radial position in an area of the inner circumference side of the recording layers  58  and  59 . With such an arrangement, the moving distance of an optical head section along the radial direction is ideally zero when the focal position of the laser light is switched from the second user data area  18  to the third user data area  19 . Thus, the processing speed can be advantageously increased. 
     Herein, the moving distance is ideally zero, i.e., may not be zero, because a deviation may occur when the recording layers  57  to  59  are combined, or because the focal position of laser light deviates to an amount corresponding to the eccentricity of the disc during the switching of the focal position of the laser light, and in such a case, a slight movement of the laser light along the radial direction is necessary. 
     An OPC region  11  is provided in each of all the recording layers  57  to  59  because the recording layers  57  to  59  have different recording characteristics. Thus, the OPC region  11  is provided in each of the recording layers  57  to  59  such that calibration of the recording power can be performed separately in any recording layer. 
     Each of the sizes of the head spare area  105 , the intermediate spare areas  106 ,  106 ′,  108  and  108 ′, and the end spare area  107  may be zero. For example, in the case where each of the sizes of the head spare area  105  and the intermediate spare areas  106 ,  106 ′,  108  and  108 ′ are not zero, and the size of the end spare area  107  is zero, the above described advantages of the present invention can be achieved. 
       FIG. 13  shows a data structure of a DDS  20  according to embodiment 2 of the present invention. The DDS  20  includes a DDS identifier  201 , a recording layer number  209 , a LSN 0  position  202 , a head spare area size  203 , an intermediate spare area size  210  at the inner circumference side, an outer circumference side intermediate spare area size  211 , the end spare area size  205 , a first layer user data area size  212 , an intermediate layer user data area size  213 , the end layer user data area size  214 , and a spare full flag group  208 . In  FIG. 13 , like elements are indicated by like reference numerals used in embodiment 1, and detailed descriptions thereof are omitted. The recording layer number  209  indicates the total number of recording layers. The inner circumference side intermediate spare area size  210  indicates the number of sectors in the intermediate spare areas  108  and  108 ′ at the inner circumference side. The outer circumference side intermediate spare area size  211  indicates the number of sectors in the intermediate spare areas  106  and  106 ′ at the inner circumference side. The first layer user data area size  212  indicates the number of sectors in the first user data area  17 . The first layer user data area size  212  is equal to the maximum value of the LSN assigned to the first user data area  17 , and therefore, is equal to the first layer last LSN  206  in embodiment 1. The intermediate layer user data area size  213  indicates the number of sectors in the second user data area  18 . The intermediate layer user data area size  213  indicates the number of sectors in the second user data area  18 . The end layer user data area size  214  indicates the number of sectors in the third user data area  19 . 
     The DDS  20  shown in  FIG. 13  can be applied to any multi-layered information recording medium having two or more recording layers. For example, consider that the DDS  20  is applied to a multi-layered information recording medium having four recording layers. In this case, the recording layer number  209  is four. The intermediate layer user data area size  213  indicates the number of sectors in the user data area of the second recording layer, and also indicates the number of sectors in the user data area of the third recording layer. The end layer user data area size  214  indicates the number of sectors in the user data area of the fourth recording layer. 
     If the region layout is limited such that the number of sectors included in the intermediate spare areas  108  and  108 ′ at the inner circumference side is the same as the number of sectors included in the intermediate spare areas  106  and  106 ′ at the outer circumference side, two information fields, the inner circumference side intermediate spare area size  210  and the outer circumference side intermediate spare area size  211 , can be gathered into a single information field because in such a case the size  210  and the size  211  are always equal. This information field is equivalent to the intermediate spare area size  204  described in embodiment 1. If the region layout is limited such that the number of sectors included in the head spare area  105  is the same as the number of sectors included in the intermediate spare areas  108  and  108 ′ at the inner circumference side, the head spare area size  203  and the intermediate spare area size  210  can be gathered into a single information field. Further, the first layer user data area size  212  and the intermediate layer user data area size  213  may be gathered into a single information field. Thus, information fields which include the identical contents when a certain limitation is made to the region layout can be reduced into a single information field including such a content, and a field obtained by four rules of arithmetic (addition, subtraction, multiplication, and division) may be omitted. 
       FIG. 14  illustrates an example of the spare full flag group  208 . The head spare area full flag  221  corresponds to the head spare area  105 . The first-layer intermediate spare area full flag  222  corresponds to the intermediate spare area  106 . An intermediate spare area full flag  225  for the outer circumference side of the second layer corresponds to the intermediate spare area  106 ′. An intermediate spare area full flag  226  for the inner circumference side of the second layer corresponds to the intermediate spare area  108 . An intermediate spare area full flag  227  for the inner circumference side of the third layer corresponds to the intermediate spare area  108 ′. The end spare area full flag  224  corresponds to the end spare area  107 . 
     The data structure shown in  FIG. 9  can also be applied to the DL  21  of embodiment 2 as in embodiment 1. If the layer number  306  is represented in the 4-bit format, 16 recording layers at the most can be expressed. In embodiment 2 also, defect sectors can be replaced with spare sectors until the spare sectors of all the recording layers are used up. It is clearly appreciated that in such an arrangement, the spare areas can be efficiently used. 
       FIG. 15  shows assignment of sector numbers according to embodiment 2 of the present invention. The sector numbers assigned from the inner circumference to the outer circumference in the first recording layer  57 , from the outer circumference to the inner circumference in the second recording layer  58 , and then from the inner circumference to the outer circumference in the third recording layer  59 , are arranged horizontally from left to right in the drawing. Thus, from left to right in the drawing, the head spare area  105 , the first user data area  17 , the intermediate spare area  106 , the intermediate spare area  106 ′, the second user data area  18 , the intermediate spare area  108 , the intermediate spare area  108 ′, the third user data area  19 , and the end spare area  107  occur in this order. In the first recording layer  57 , the PSN increases by 1 every time a single sector is passed toward the outer circumference side. In the second recording layer  52 , the PSN increases by 1 every time a single sector is passed toward the inner circumference side. In the third recording layer  59 , the PSN increases by 1 every time a single sector is passed toward the outer circumference side. The assignment directions of LSNs are opposite between contiguous recording layers. The assignment may be made such that values obtained by removing the layer number from the PSNs are in the same numeric range among the first to third recording layers  57  to  59 . Alternatively, a rule of assigning PSNs in the opposite paths of a DVD-ROM may be extended such that the relationship between the values of lower bits of the PSN of a sector in an odd-numbered layer and the values of lower bits of the PSN of a sector in an even-numbered layer at the same radial position may be two&#39;s complement. In this case, as values of higher bits of the PSNs, 0 may be assigned to the first and second recording layers, 1 may be assigned to the third and fourth recording layers, and 2 may be assigned to the fifth and sixth recording layers. 
     The LSNs are assigned only to sectors included in the user data area  5 . In the first user data area  17 , 0 is assigned as the LSN of the sector at the innermost circumference position, and the LSN increases by 1 every time a single sector is passed from the inner circumference side to the outer circumference side. In the second user data area  18 , a value obtained by adding 1 to the maximum LSN of the first user data area  17  is assigned as the LSN of the sector at the outermost circumference position, and the LSN increases by 1 every time a single sector is passed from the outer circumference side to the inner circumference side. In the third user data area  19 , a value obtained by adding 1 to the maximum LSN of the second user data area  18  is assigned as the LSN of the sector at the innermost circumference position, and the LSN increases by 1 every time a single sector is passed from the inner circumference side to the outer circumference side. 
     Although a detailed description is herein omitted because it is substantially the same as that provided in embodiment 1, even if user data has already been recorded in the user data area  5  of a multi-layered information recording medium including three or more recording layers, the size of the outermost circumference spare area  107  can be increased. 
     As described above, according to embodiment 2, continuous accessibility can be improved in a multi-layered information recording medium including two or more recording layers. Furthermore, a defect sector can be replaced with a spare area in any recording layer, and therefore, the spare areas can be efficiently used. Furthermore, the size of the spare area can be increased so as to prevent lack of spare areas, whereby reliability of data can be improved. 
     Embodiment 3 
     Hereinafter, a multi-layered information recording medium according to embodiment 3 of the present invention is described with reference to the drawings. 
       FIG. 16  shows a region layout of a multi-layered information recording medium  60  according to embodiment 3 of the present invention. The multi-layered information recording medium  60  includes two recording layers  61  and  62 . The recording/reproduction direction is the same in both the first and second recording layers  61  and  62 . The multi-layered information recording medium  60  includes a user data area  5  for recording user data. The first recording layer  61  includes, from the inner circumference side to the outer circumference side, a lead-in zone  101 , a head spare area  105 , a first user data area  23 , which is a portion of the user data area  5 , an intermediate spare area  106 , and a lead-out zone  111 . The second recording layer  62  includes, from the inner circumference side to the outer circumference side, a lead-in zone  110 , an intermediate spare area  108 , a second user data area  24 , which is a portion of the user data area  5 , an end spare area  107 , and a lead-out zone  104 . The lead-out zone  111  includes a defect management region  12 . The lead-in zone  110  includes an OPC region  11 . In  FIG. 16 , like elements are indicated by like reference numerals used in embodiment 1 or 2, and detailed descriptions thereof are omitted. 
     The DDS  20  of embodiment 2 shown in  FIG. 13  can also be used as the data structure of embodiment 3. In embodiment 3, it is not necessary to provide the intermediate layer user data area size  213 . 
     In embodiment 3, the flag group shown in  FIG. 8  is used as the spare full flag group  208  of embodiment 3. 
     In embodiment 3, the data structure shown in  FIG. 9  is used as the DL  21  of embodiment 3. In embodiment 3 also, defect sectors can be replaced with spare sectors until the spare sectors of all the recording layers are used up. It is clearly appreciated that in such an arrangement, the spare areas can be efficiently used. 
       FIG. 17  shows assignment of sector numbers according to embodiment 3 of the present invention. The sector numbers assigned from the inner circumference to the outer circumference in the first recording layer  61 , and then from the inner circumference to the outer circumference in the second recording layer  62 , are arranged horizontally from left to right in the drawing. Thus, from left to right in the drawing, the head spare area  105 , the first user data area  23 , the intermediate spare area  106 , the intermediate spare area  108 , the second user data area  24 , and the end spare area  107  occur in this order. In both the first recording layer  61  and the second recording layer  62 , the PSN increases by 1 every time a single sector is passed from the inner circumference side to the outer circumference side. The PSNs in the first and second layers at the same radial position are equal except for layer numbers. The LSNs are assigned only to sectors included in the user data area  5 . In the first user data area  23 , 0 is assigned as the LSN of the sector at the innermost circumference position, and the LSN increases by 1 every time a single sector is passed from the inner circumference side to the outer circumference side. In the second user data area  24 , a value obtained by adding 1 to the maximum LSN of the first user data area  23  is assigned as the LSN of the sector at the innermost circumference position, and the LSN increases by 1 every time a single sector is passed from the inner circumference side to the outer circumference side. 
     It is clear from the comparison made between  FIGS. 10 and 17 , even if the recording/reproduction direction in a recording layer is different between the multi-layered information recording medium  50  of embodiment 1 and the multi-layered information recording medium  60  of embodiment 3, the relationship between assignment of LSNs and disposition of the spare areas is the same. Thus, as described in embodiment 1, even if user data has already been recorded in the user data area  5 , the size of spare areas can be increased. 
     As described above, according to embodiment 3, for multi-layered information recording mediums having two or more recording layers, a common defect management method can be applied to both a multi-layered information recording medium wherein the recording/reproduction direction is the same in all of the recording layers and a multi-layered information recording medium wherein the recording/reproduction direction is alternately inverted for the respective recording layers. Thus, a defect sector can be replaced with a spare area of any recording layer, and therefore, the spare areas can be efficiently used. Furthermore, the size of the spare area can be increased so as to prevent lack of spare areas, whereby reliability of data can be improved. 
     Embodiment 4 
     Hereinafter, an embodiment of an information recording/reproducing apparatus, which performs recording/reproduction using the multi-layered information recording medium  50  described in embodiment 1, is described with reference to the drawings. 
       FIG. 18  is a block diagram showing an information recording/reproducing apparatus  500  according to embodiment 4 of the present invention. The information recording/reproducing apparatus  500  includes a disc motor  502 , a preamplifier  508 , a servo circuit  509 , a binarization circuit  510 , a modulation/demodulation circuit  511 , an ECC circuit  512 , a buffer  513 , a CPU  514 , an internal bus  534 , and an optical head section  535 . In the information recording/reproducing apparatus  500 , the multi-layered information recording medium  50  is inserted. The optical head section  535  includes a lens  503 , an actuator  504 , a laser driving circuit  505 , a light detector  506 , and a transport table  507 . Reference numeral  520  denotes a rotation detection signal. Reference numeral  521  denotes a disc motor driving signal. Reference numeral  522  denotes a laser emission permitting signal. Reference numeral  523  denotes a light detection signal. Reference numeral  524  denotes a servo error signal. Reference numeral  525  denotes an actuator driving signal. Reference numeral  526  denotes a transport table driving signal. Reference numeral  527  denotes an analog data signal. Reference numeral  528  denotes a binarization data signal. Reference numeral  529  denotes a demodulation data signal. Reference numeral  530  denotes a correction data signal. Reference numeral  531  denotes a storage data signal. Reference numeral  532  denotes an encode data signal. Reference numeral  533  denotes a modulation data signal. 
     The CPU  514  functions as a control section. The CPU  514  controls the entire operation of the information recording/reproducing apparatus  500  via the internal bus  534  according to an incorporated control program. As described below, the optical head section  535  can optically write information in the multi-layered information recording medium  50  from one side of the multi-layered information recording medium  50 . The optical head section  535  can optically read information from the multi-layered information recording medium  50 . The CPU  514  controls execution of a defect management process using the optical head section  535  as described below. 
     In response to the laser emission permitting signal  522  output from the CPU  514 , the laser driving circuit  505  emits laser light  536  onto the multi-layered information recording medium  50 . The light reflected by the multi-layered information recording medium  50  is converted by the light detector  506  to the light detection signal  523 . The light detection signal  523  is subjected to addition/subtraction in the preamplifier  508  so as to generate the servo error signal  524  and the analog data signal  527 . The analog data signal  527  is A/D (analog/digital) converted by the binarization circuit  510  to the binarization data signal  528 . The binarization data signal  528  is demodulated by the modulation/demodulation circuit  511  to generate the demodulation data signal  529 . The demodulation data signal  529  is converted by the ECC circuit  512  to the correction data signal  530  which does not include any error. The correction data signal  530  is stored in a buffer  513 . The servo circuit  509  outputs the actuator driving signal  525  based on the servo error signal  524 , thereby feeding a servo error back to the actuator  504  for focusing control or tracking control of the lens  503 . An error correction code is added by the ECC circuit  512  to the storage data signal  531  which is an output of data from the buffer  513 , so as to generate the encode data signal  532 . Then, the encode data signal  532  is modulated by the modulation/demodulation circuit  511  to generate the modulation data signal  533 . The modulation data signal  533  is input to the laser driving circuit  505  so as to modulate the power of laser light. 
     The information recording/reproducing apparatus  500  may be used as a peripheral device of a computer, such as a CD-ROM drive or the like. In such a case, a host interface circuit (not shown) is additionally provided, and data is transmitted between a host computer (not shown) and the buffer  513  through a host interface bus (not shown) such as a SCSI or the like. Alternatively, if the information recording/reproducing apparatus  500  concomitantly works as a consumer device such as a CD player or the like, an AV decoder/encoder circuit (not shown) is additionally provided for compressing a moving image or sound or decompressing a compressed moving image or sound in order to transmit data between the host computer and the buffer  513 . 
     In a reproduction operation of the information recording/reproducing apparatus  500  according to embodiment 4 of the present invention, it is necessary to provide two processes, a process of obtaining defect management information and a process of reproducing sectors while considering replacement, in order to reproduce information recorded in the multi-layered information recording medium  50  including two recording layers to which defect management of the present invention is applied. 
     In a recording operation of the information recording/reproducing apparatus  500  according to embodiment 4 of the present invention, it is necessary to provide, in addition to the above reproduction operation, two processes, a process of updating defect management information and a process of recording sectors while considering replacement, in order to record information in the multi-layered information recording medium  50  including two recording layers to which defect management of the present invention is applied. 
       FIG. 19  shows a flowchart  600  for illustrating a procedure of obtaining defect management information in embodiment 4 of the present invention. In this embodiment, the disc information zone  10 , in which disc information is stored, and a defect management region  12 , in which defect management information is stored, are provided in a reference layer. 
     At the first step of the process of obtaining defect management information, i.e., at step  601 , the CPU  514  instructs the servo circuit  509  to control the focal point of laser light so as to follow a track of a reference layer. 
     At step  602 , the optical head section  535  reproduces a sector which stores disc information, and the CPU  514  confirms parameters and formats which are necessary for recording/reproduction in the multi-layered information recording medium  50 . 
     At step  603 , the optical head section  535  reproduces a sector which stores defect management information. The reproduced data is retained in a predetermined place of the buffer  513 . 
       FIG. 20  is a flowchart  700  for illustrating a reproduction procedure of sectors according to embodiment 4 of the present invention, wherein replacement is considered. In this reproduction process, assume that defect management information including the DDS  20  and DL  21  have already been retained in the buffer  513 . 
     At the first step of this reproduction process, i.e., at step  701 , the CPU  514  converts the LSNs to PSNs (detailed descriptions of this step will be described later with reference to  FIG. 21 ). 
     At step  702 , the CPU  514  refers to the layer number of the PSN to determine whether or not a recording layer in which the focal point of the laser light  536  exists is identical to a recording layer to be reproduced. If identical, the process proceeds to step  704 ; if not, the process proceeds to step  703 . 
     At step  703 , the CPU  514  instructs the servo circuit  509  to let the focal point of the laser light  536  to follow a track of a recording layer to be reproduced. 
     At step  704 , the optical head section  535  reproduces information recorded in a sector indicated by the PSN obtained at conversion step  701 . 
       FIG. 21  is a flowchart  800  for illustrating a procedure of converting LSNs to PSNs (i.e., step  701  of  FIG. 20 ) according to embodiment 4 of the present invention. In this embodiment, assume that in the first recording layer, the PSN increases by 1 every time one sector is passed from the inner circumference side to the outer circumference side, while in the second recording layer, the PSN increases by 1 every time one sector is passed from the outer circumference side to the inner circumference side. 
     At the first step of this replacement process, i.e., at step  801 , the LSNs are converted to PSNs without considering a result of replacement of defect sectors indicated in the DL  21  with spare areas (i.e., in the same manner as that performed when no defect sector exists). Referring to  FIG. 10 , if an LSN to be converted is smaller than the total number of sectors included in the first user data area  15 , a corresponding PSN is obtained by calculation of (the minimum PSN of the first user data area  15 ) plus (the LSN). If an LSN to be converted is greater than the total number of sectors included in the first user data area  15 , a corresponding PSN is obtained by calculation of (the minimum PSN of the second user data area  16 ) plus (the LSN) minus (the total number of sectors included in the first user data area  15 ). 
     At step  802 , the CPU  514  refers to the DL entries  303  of the DL  21  to determine whether or not a sector indicated by the above-calculated PSN has been replaced with a spare sector. If so, the process proceeds to step  803 ; if not, the replacement process ends. 
     At step  803 , a replacement sector position of the DL entry  303 , which indicates that the sector having the above PSN has been replaced, is employed as a PSN. 
     As described above, the information recording/reproducing apparatus  500  according to embodiment 4 of the present invention can reproduce information recorded in the multi-layered information recording medium  50  having two recording layers to which defect management of the present invention is applied. The reproduction operation of user data which is performed after the focal point of the laser light  536  has been moved to a recording layer to be accessed, is basically the same as the reproduction operation of user data performed for a single-layered information recording medium. Thus, it is clearly appreciated that any user data reproduction procedure for an information recording/reproducing apparatus designed for a single-layered disc can be used. 
       FIG. 22  is a flowchart for illustrating a procedure of updating defect management information according to embodiment 4 of the present invention. In this embodiment, assume that a formatting process for the multi-layered information recording medium  50  includes an initialization process for defect management information and a process of increasing the size of a spare area. 
     At the first step of this updating process, i.e., at step  901 , the CPU  514  determines whether or not a necessary formatting process is a process of increasing the size of a spare area. If so, the process proceeds to step  902 ; if not, the process proceeds to step  903 . 
     At step  902 , the CPU  514  sets a value of the end spare area size  205  of the DDS  20  ( FIG. 7 ). 
     At step  903 , the CPU  514  sets the respective values of the DDS  20  to predetermined values of the device, and sets the DL entry number  302  of the DL  21  to 0. 
     At step  904 , the CPU  514  determines whether or not the focal point of the laser light  536  is following a track of a reference layer. If so, the process proceeds to step  906 ; if not, the process proceeds to step  905 . 
     At step  905 , the CPU  514  instructs the servo circuit  509  to let the focal point of the laser light  536  to follow the track of the reference layer. 
     At step  906 , the optical head section  535  records defect management information, including the DDS  20  and DL  21 , in a sector included in the defect management region  12 . 
       FIG. 23  is a flowchart  1000  for illustrating a recording procedure in sectors according to embodiment 4 of the present invention, wherein replacement is considered. 
     At the first step of this recording process, i.e., at step  1001 , the CPU  514  converts the LSNs to the PSNs according to the procedure shown in  FIG. 21 . 
     At step  1002 , the CPU  514  refers to the layer number of the PSN to determine whether or not a recording layer in which the focal point of the laser light  536  exists is identical to a recording layer in which information is to be recorded. If identical, the process proceeds to step  1004 ; if not, the process proceeds to step  1003 . 
     At step  1003 , the CPU  514  instructs the servo circuit  509  to let the focal point of the laser light  536  to follow a track of the recording layer in which information is to be recorded. 
     At step  1004 , information is recorded in a sector indicated by the PSN obtained at conversion step  1001 . 
     At step  1005 , the CPU  514  controls the optical head section  535  to reproduce the information recorded in the sector, thereby determining whether or not recording of the information in the sector was successful (i.e., whether or not a defect sector exists in the user data area  5 ). If successful, the recording process ends; if not, the process proceeds to step  1006 . 
     At step  1006 , the CPU  514  assigns a spare sector to a defect sector, thereby replacing the defect sector with the spare sector (details of the process of assigning a spare sector will be described later with reference to  FIGS. 24A and 24B ). 
     At step  1007 , it is determined whether or not the process of replacing the defect sector with the spare sector was impossible. If impossible, the recording process ends; if possible, the process returns to step  1001 . 
       FIG. 24A  is a flowchart for illustrating an assignment procedure of spare sectors according to embodiment 4 of the present invention. 
     The process of assigning spare sectors includes a process of finding at least one available spare area among a plurality of spare areas included in the multi-layered information recording medium  50 , and a process of selecting, from the found at least one available spare area, a spare area which is closest to a defect sector. The details of the process of assigning spare sectors are described below with reference to  FIG. 24A . 
     At the first step of the spare sector assignment process, i.e., at step  1101 , the CPU  514  refers to the spare full flag group  208  ( FIG. 8 ) to determine whether or not the multi-layered information recording medium  50  has an available spare area. If there is no available spare area, the CPU  514  determines that the assignment process is impossible and accordingly terminates the assignment process. If there is an available spare area, the process proceeds to step  1102 . 
     At step  1102 , the CPU  514  determines whether the radial position of a defect sector is closer to a spare area at the inner circumference side or closer to a spare area at the outer circumference side. If the radial position of the defect sector is closer to a spare area at the inner circumference side, the process proceeds to step  1103 . If the radial position of the defect sector is closer to a spare area at the outer circumference side, the process proceeds to step  1104 . 
     At step  1103 , the CPU  514  refers to the spare full flag group  208  to determine whether or not the spare area at the inner circumference side is available. If available, the process proceeds to step  1105 ; if not, the process proceeds to step  1106 . 
     At step  1104 , the CPU  514  refers to the spare full flag group  208  to determine whether or not the spare area at the outer circumference side is available. If available, the process proceeds to step  1106 ; if not, the process proceeds to step  1105 . 
     At step  1105 , the CPU  514  refers to the spare full flag group  208  to determine whether or not a spare area which is in a recording layer where the defect sector exists, and which is at the inner circumference side, is available. If available, the process proceeds to step  1107 ; if not, the process proceeds to step  1108 . 
     At step  1106 , the CPU  514  refers to the spare full flag group  208  to determine whether or not a spare area which is in a recording layer where the defect sector exists, and which is at the outer circumference side, is available. If available, the process proceeds to step  1109 ; if not, the process proceeds to step  1110 . 
     At step  1107 , the CPU  514  assigns a spare sector included in the spare area which is in a recording layer where the defect sector exists, and which is at the inner circumference side, to the defect sector. 
     At step  1108 , the CPU  514  assigns a spare sector included in a spare area which is in a recording layer different from the recording layer where the defect sector exists, and which is at the inner circumference side, to the defect sector. 
     At step  1109 , the CPU  514  assigns a spare sector included in a spare area which is in a recording layer where the defect sector exists, and which is at the outer circumference side, to the defect sector. 
     At step  1110 , the CPU  514  assigns a spare sector included in a spare area which is in a recording layer different from the recording layer where the defect sector exists, and which is at the outer circumference side, to the defect sector. 
     In the spare sector assignment procedure shown in  FIG. 24A , a spare sector included in a spare area, whose radial distance from the defect sector is shortest, is used as a spare sector. If the radial distance is shorter, the time required for a seek operation, which is accompanied by a movement of the transport table  507 , becomes shorter. According to the present invention, a different assignment procedure may be used so long as an objective of the present invention, i.e., using a spare sector whose radial distance from a defect sector is shortest as a spare sector, is attained. 
       FIG. 24B  shows a flowchart  1120  which illustrates an alternative spare sector assignment process according to embodiment 4 of the present invention. 
     This alternative assignment process includes the following processes: a process of finding at least one available spare area among a plurality of spare areas included in the multi-layered information recording medium  50 ; a process of determining whether or not at least one of the found available spare areas exists in a recording layer where a portion of the user data area  5  including a defect sector exists; and a process of selecting a spare area which is closest to the defect sector from the at least one found available spare area if it is determined that none of the at least one found spare area exists in the recording layer where the defect sector exists. The details of the process of assigning spare sectors are described below with reference to  FIG. 24B . 
     At the first step of the spare sector assignment process, i.e., at step  1121 , the CPU  514  refers to the spare full flag group  208  to determine whether or not the multi-layered information recording medium  50  has an available spare area. If there is no available spare area, the CPU  514  determines that the assignment process is impossible and accordingly terminates the assignment process. If there is an available spare area, the process proceeds to step  1122 . 
     At step  1122 , the CPU  514  refers to the spare full flag group  208  to determine whether or not a spare area included in a recording layer in which a defect sector exists is available. If available, the process proceeds to step  1123 ; if not, the process proceeds to step  1124 . 
     At step  1123 , the CPU  514  determines whether the radial position of a defect sector is closer to a spare area at the inner circumference side or closer to a spare area at the outer circumference side. If the radial position of the defect sector is closer to a spare area at the inner circumference side, the process proceeds to step  1125 . If the radial position of the defect sector is closer to a spare area at the outer circumference side, the process proceeds to step  1127 . 
     At step  1125 , the CPU  514  refers to the spare full flag group  208  to determine whether or not a spare area residing at the inner circumference side of that recording layer is available. If available, the process proceeds to step  1129 ; if not, the process proceeds to step  1131 . 
     At step  1127 , the CPU  514  refers to the spare full flag group  208  to determine whether or not a spare area residing at the outer circumference side of that recording layer is available. If available, the process proceeds to step  1131 ; if not, the process proceeds to step  1129 . 
     The processes of steps  1124 ,  1126 , and  1128  are the same as those of steps  1123 ,  1125 , and  1127 , respectively, except that a recording layer including a spare area which is to be used is different from a recording layer including the defect sector. 
     At step  1129 , the CPU  514  assigns a spare sector included in the spare area which is in a recording layer where the defect sector exists, and which is at the inner circumference side, to the defect sector. 
     At step  1130 , the CPU  514  assigns a spare sector included in a spare area which is in a recording layer different from the recording layer where the defect sector exists, and which is at the inner circumference side, to the defect sector. 
     At step  1131 , the CPU  514  assigns a spare sector included in a spare area which is in a recording layer where the defect sector exists, and which is at the outer circumference side, to the defect sector. 
     At step  1132 , the CPU  514  assigns a spare sector included in a spare area which is in a recording layer different from the recording layer where the defect sector exists, and which is at the outer circumference side, to the defect sector. 
     The spare sector assignment procedure shown in  FIG. 24B  uses a spare sector in a spare area included in a recording layer in which a defect sector exists so long as such a spare sector is available. By using such a spare sector included in a recording layer in which a defect sector exists, it is not necessary to change different recording parameters for respective recording layers. For example, if in an information recording operation in a recording layer, the recording power is not optimally calibrated for the other recording layers, the assignment procedure shown in  FIG. 24B  can be performed faster than the assignment procedure shown in  FIG. 24A . According to the present invention, a different assignment procedure may be used so long as an objective of the present invention, i.e., using a spare sector in a spare area included in a recording layer in which a defect sector exists so long as such a spare sector is available, is attained. 
     As described above, the information recording/reproducing apparatus  500  according to embodiment 4 of the present invention can record information in the multi-layered information recording medium  50  having two recording layers to which defect management of the present invention is applied. The information recording/reproducing apparatus  500  can assign a spare sector selected from a spare area included in a recording layer which is different from a recording layer in which a defect sector exists. The information recording/reproducing apparatus  500  can perform a process of assigning a spare sector while giving a greater weight to reduction of the seek time as described above with reference to  FIG. 24A . Further, the information recording/reproducing apparatus  500  can perform a process of assigning a spare sector while giving a greater weight to reduction of the time required for setting the recording power as described above with reference to  FIG. 24B . Herein, an operation performed after an optical head section reaches a recording layer to be accessed is basically the same as that performed on a single-layered information recording medium. Thus, it is clearly appreciated that any recording procedure arranged for an information recording/reproducing apparatus designed for a single-layered information recording medium can be used. 
     The recording operation in the user data area which is performed after the focal point of the laser light  536  has been moved to a recording layer to be accessed, is basically the same as the recording operation of user data performed for a single-layered information recording medium. Thus, it is clearly appreciated that any user data recording procedure for recording in a user data area, which is adapted for an information recording/reproducing apparatus designed for a single-layered disc, can be used. 
     Although the multi-layered information recording medium  50  described in embodiment 1 was used to explain embodiment 4 of the present invention, it is clearly appreciated that the multi-layered information recording medium  60  described in embodiment 3 can also be used. Further, it is also clearly appreciated that the multi-layered information recording medium  56  described in embodiment 2 can also be used when the conversion processing at step  801  shown in  FIG. 21  is applied to three or more recording layers. 
     Although in the above descriptions of the present invention, reproduction/recording of information and defect management are performed on the units of a sector, it is clearly appreciated that the present invention is applicable even when reproduction/recording of information and defect management is performed on the units of a block which includes a plurality of sectors, or on the units of an ECC block which is, for example, a unit based on which an error correction code of a DVD disc is calculated. For example, in the case where the above operations are performed on the units of an ECC block, a plurality of sectors included in the ECC block in which a defect sector exists are replaced with a plurality of spare sectors, whereby the defect sector is replaced with a spare sector. Such a modified embodiment is made within the spirit and applicable range of the present invention, and any modified embodiment which is readily appreciated by those skilled in the art, falls within the scope of the claims of the present invention. 
     According to a multi-layered information recording medium of the present invention, one recording layer includes defect management information for all the recording layers. With such an arrangement, the defect management information for all the recording layers can be obtained by simply accessing the one recording layer. Thus, continuous accessibility can be improved. 
     According to a multi-layered information recording medium of the present invention, a first spare area which is positioned so as to be contiguous to a first user data area and a second spare area which is positioned so as to be contiguous to a second user data area are placed approximately at the same radial position on the multi-layered information recording medium. With this arrangement, when the focal position of laser light transits from the first user data area to the second user data area, the moving distance of an optical head section along the radial direction is ideally zero (0). Thus, continuous accessibility can be improved. 
     According to a multi-layered information recording medium of the present invention, a detected defect sector can be replaced with a spare area of any recording layer. Thus, spare areas can be efficiently used, and reliability of data can be improved. 
     According to a multi-layered information recording medium of the present invention, when the number of defect sectors is greater than what is expected, the defect sectors can be replaced with spare sectors by increasing the size of a spare area. Thus, reliability of data can be improved. 
     According to a multi-layered information recording medium of the present invention, consecutive numbers are assigned as LSNs to the user data areas throughout all the recording layers. With such an arrangement, a common defect management method can be applied to both a multi-layered information recording medium wherein the recording/reproduction direction is the same in all of the recording layers and a multi-layered information recording medium wherein the recording/reproduction direction is alternately inverted for the respective recording layers. Thus, the cost of production and development of the multi-layered information recording medium can be reduced. 
     According to a multi-layered information recording medium of the present invention, control information regions such as a region for storing recording/reproduction parameters, a region for storing defect management information, or the like, are provided in one recording layer. With such an arrangement, the control information for all the recording layers can be obtained by simply accessing the one recording layer. Thus, continuous accessibility can be improved. 
     According to a multi-layered information recording medium of the present invention, control information regions are provided in a reference layer. Thus, recording/reproduction operations can be performed in strict conformity with the information in the control information regions. 
     According to a multi-layered information recording medium of the present invention, every recording layer has its OPC region for calibrating the recording power. With such an arrangement, the recording power can be optimally calibrated for each recording layer. 
     According to an information reproduction method and information reproduction apparatus of the present invention, information can be reproduced from a multi-layered information recording medium which includes defect management information about a plurality of recording layers. 
     According to an information recording method and information recording apparatus of the present invention, information can be recorded in a multi-layered information recording medium which includes defect management information about a plurality of recording layers. 
     According to an information recording method and information recording apparatus of the present invention, a defect sector is replaced with a spare sector included in a spare area which is closer to the defect sector. With such an arrangement, assignment of a spare sector can be performed while giving a greater weight to reduction of the time required for seeking along the radial direction. 
     According to an information recording method and information recording apparatus of the present invention, a defect sector is replaced with a spare sector included in a spare area residing in a recording layer in which the defect sector exists. With such an arrangement, assignment of a spare sector can be performed while giving a greater weight to reduction of the time required for setting the recording power. 
     Various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the scope and spirit of this invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the description as set forth herein, but rather that the claims be broadly construed.