Patent Publication Number: US-2006018635-A1

Title: Optical disk, optical disk drive, and optical disk recording method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-217597, filed Jul. 26, 2004, the entire contents of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an optical disk, such as a DVD (Digital Versatile Disk), and more particularly to a multi-layered optical disk having improved information recording layers.  
      The present invention also relates to an optical disk drive and an optical disk recording method for recording information in the multi-layered optical disk.  
      2. Description of the Related Art  
      As is well known, the technology for recording information with high density is being developed in recent years, and recent optical disks include a disk having a storage capacity of 4.7 GB (Giga Byte) on one side thereof. Such an optical disk is realized as DVD-R (recordable DVD), DVD-RW (rewritable DVD), DVD-RAM (random access memory), or the like.  
      At the present time, information is recorded on an optical disk at a speed several times faster than the standard recording speed (linear velocity) (3.49 m/s) defined for an ordinary type of optical disk.  
      To enhance the recording density, the optical disk may be provided with information recording layers arranged at multi-levels.  
      Jpn. Pat. Appln. KOKAI Publication No. 2001-184642 discloses how to prevent the erasing of data when it is recorded by a read modify write process.  
      However, Jpn. Pat. Appln. KOKAI Publication No. 2001-184642 does not disclose a technology for speeding up the recording speed of an optical disk. Nor does that reference disclose a technology for providing multi-layered optical disk.  
     BRIEF SUMMARY OF THE INVENTION  
      Accordingly, an object of the present invention is to provide an optical disk, an optical disk drive and an optical disk recording method, which optimize the recording conditions for each information recording layer of a multi-layered optical disk in accordance with the recording speed.  
      To achieve the above object, the present invention provides an optical disk comprising a first information recording layer including a first inward test recording area and a first outward test recording area; and 
          a second information recording layer including a second inward test recording area and a second outward test recording area, wherein at least one recording management area is formed in at least one of the first information recording layer and the second information recording layer and records recording management information which is obtained when test recording is performed for at least one of the first and the second inward test recording areas and the first and the second outward test recording areas.        

      The present invention also provides an optical disk drive used with an optical disk comprising a first information recording layer including a first inward test recording area and a first outward test recording area; and a second information recording layer including a second inward test recording area and a second outward test recording area, wherein at least one recording management area is formed in at least one of the first information recording layer and the second information recording layer and records recording management information which is obtained when test recording is performed for at least one of the first and the second inward test recording areas and the first and the second outward test recording areas, the optical disk drive comprising: 
          first control means for (i) determining recording conditions by performing test recording for one of the first inward test recording area and the first outward test recording area in accordance with a requested recording speed when a request for recording information in the first information recording layer is made, (ii) recording the information in the first information recording layer based on the determined recording conditions, and (iii) recording management information, obtained when the test recording is performed for one of the first inward test recording area and the first outward test recording area, in the recording management area; and     second control means for (i) determining recording conditions by performing test recording for one of the second inward test recording area and the second outward recording area in accordance with a requested recording speed when a request for recording information in the second information recording layer is made, (ii) recording the information in the second information recording layer based on the determined recording conditions, and (iii) recording management information, obtained when the test recording is performed for one of the second inward test recording area and the second outward test recording area, in the recording management area.        

      The present invention further provides an optical disk recording method for an optical disk comprising a first information recording layer including a first inward test recording area and a first outward test recording area; and a second information recording layer including a second inward test recording area and a second outward test recording area, wherein at least one recording management area is formed in at least one of the first information recording layer and the second information recording layer and records recording management information which is obtained when test recording is performed for at least one of the first and the second inward test recording areas and the first and the second outward test recording areas, the method comprising: 
          a first step of determining recording conditions by performing test recording for one of the first inward test recording area and the first outward test recording area in accordance with a requested recording speed when a request for recording information in the first information recording layer is made;     a second step of (i) recording the information in the first information recording layer based on the recording conditions determined in the first step, and (ii) recording management information, obtained when the test recording is performed for one of the first inward test recording area and the first outward test recording area, in the recording management area;     a third step of determining recording conditions by performing test recording for one of the second inward test recording area and the second outward test recording area in accordance with a requested recording speed when a request for recording information in the second information recording layer is made; and     a fourth step of (i) recording the information in the second information recording layer based on the recording conditions determined in the third step, and (ii) recording management information, obtained when the test recording is performed for one of the second inward test recording area and the second outward test recording area, in the recording management area.        

      Additional advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
      The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
       FIG. 1  is a block circuit diagram illustrating an optical disk drive and an optical disk which are according to an embodiment of the present invention;  
       FIGS. 2A, 2B , and  2 C illustrate a PTP type optical disk that is used with the optical disk drive according to the embodiment;  
       FIG. 3  is a flowchart illustrating part of the optical disk recording operation according to the embodiment;  
       FIG. 4  is a flowchart illustrating the remaining part of the optical disk recording operation according to the embodiment;  
       FIGS. 5A, 5B , and  5 C illustrate an OTP type optical disk that is used with the optical disk drive according to the embodiment;  
       FIGS. 6A, 6B , and  6 C illustrate the OTP type optical disk of the embodiment in which the radial positions of middle areas are changed;  
       FIG. 7  is a flowchart illustrating part of the OTP type optical disk recording operation the embodiment; and  
       FIG. 8  is a flowchart illustrating the remaining part of the OTP type optical disk recording operation of the embodiment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      An embodiment of the present invention will now be described in detail with reference to the accompanying drawings.  
       FIG. 1  shows an optical disk drive  11  and an optical disk  12  which are according to an embodiment of the present invention.  
      The optical disk  12  is a multi-layered recordable DVD having information recording layers. The optical disk  12  is rotated by a disk motor  12  at a predetermined speed. An optical head  14  is opposed to one of the surfaces of the optical disk  12 .  
      The optical head  14  reads information out of the optical disk  12  and is movable in the radial direction of the optical disk  12 .  
      To be more specific, the optical head  14  reads information out of the optical disk  12  as follows:  
      The optical head  14  has an objective lens OL. By this objective lens, a laser beam a laser diode LD emits for the reproduction of information is focused on a target information recording layer of the optical disk  12 . The reflected beam is incident on a photodiode PD, by which it is converted into electric signals. The electric signals output from the photodiode PD are supplied to a signal processor  15 .  
      In the signal processor  15 , the electric signals are subjected to digitizing, predetermined decode processing, error correction processing and descramble processing.  
      After being subjected to these kinds of processing, the electric signals are supplied through an interface  16  to an input/output terminal  17 , from which they are output and used for the reproduction of video and audio information.  
      The optical head  14  can also write information in the optical disk  12  by focusing a recording laser beam on a target information recording layer of the optical disk  12 . The recording laser beam is emitted from the laser diode LD and is focused on the target recording layer by the objective lens OL. To be more specific, the write operation is performed as follows:  
      First, information to be written in the optical disk  12  is input from the input/output terminal  17 . The input information is supplied through the interface  16  to the signal processor  15 .  
      The signal processor  15  performs predetermined processing with respect to the input recording information, including encode processing, processing for adding error-correction codes and scramble processing. After being subjected to these kinds of processing, the recording information is supplied to a recording power controller  18 .  
      The recording power controller  18  determines appropriate recording conditions in accordance with the recording speed at which the information is to be recorded in the optical disk. Based on the determined recording conditions, the recording power controller  18  controls an LD driver  19  so that an appropriate amount of light can be emitted from the laser diode LD. In this manner, the information can be recorded under the appropriate recording conditions determined in accordance with the recording speed.  
      The electric signals output from the photodiode PD of the optical head  14  are supplied to a servo processor  20 .  
      Under the control by a servo controller  21 , the servo processor  20  generates error signals from the electric signals. The error signals correspond to a tracking error or a focusing error of the objective lens OL.  
      Based on the error signals the servo processor  20  generates, an actuator driver  22  controls the objective lens OL in both the tracking direction and focusing direction. Controlled in this manner, the objective lens OL performs a tracking servo operation and a focusing servo operation. The servo controller  21  also controls the rotation of a disk motor  13 .  
      All operations of the optical disk drive  11 , including the recording/reproduction operations described above, are controlled by a controller  23 .  
      The controller  23  incorporates a CPU (a central processing unit) or the like. Upon receipt of control information supplied from an operation section  24 , the controller  23  performs control operations in accordance with the control information.  
      When performing control, the controller  23  uses a memory section  25 .  
      The memory section  25  includes: a read-only memory which stores control programs the CPU of the controller  23  executes; a read/write memory which the CPU uses as a work area; and a nonvolatile memory which stores various types of setting information and control information.  
       FIG. 2A  shows details of the optical disk  12 .  
      The optical disk  12  comprises a circular substrate  26  made of polycarbonate. An information recording layer  27  made of a metallic material, an intermediate layer  28  made of a transparent material, an information recording layer  29  made of a semi-transparent material, and a cover layer  30  made of a transparent material are stacked on one side of the substrate  26  in the order mentioned.  
      A laser beam emitted from the optical head  14  is incident on the cover layer  30 , as indicated by the arrow in  FIG. 2A , and is selectively focused on one of the two information recording layers  29  and  27 .  
      The optical disk  12  is a PTP (parallel track path) type. That is, each of the two information recording layers  29  and  27  starts the recording/reproduction of information from a radially-inward area to a radially-outward area. To be more specific, information recording layer  29  (the first information recording layer), which is closer to the optical head  14  than information recording layer  27  is, includes a radially-inward test recoding area (PCA)  29   a , a recording management area (RMA)  29   b , a lead-in area  29   c , an information recording area  29   d , a lead-out area  29   e  and a radially-outward test recording area (PCA)  29   g . These areas are sequentially formed from the innermost circumferential position of information recording layer  29  to the outermost circumferential position thereof.  
      Likewise, information recording layer  27  (the second information recording layer), which is farther from the optical head  14  than information recording layer  29  is, includes a radially-inward test recoding area (PCA)  27   a , a lead-in area  27   c , an information recording area  27   d , a lead-out area  27   e  and a radially-outward test recording area (PCA)  29   g . These areas are sequentially formed from the innermost circumferential position of information recording layer  27  to the outermost circumferential position thereof.  
      A description will now be given as to how information is recorded in the information recording area  29   d  of the first information recording layer  29  at the standard speed (i.e., 3.49 m/s) or at a speed slower than the quadruple speed (which is four times faster than the standard speed). In this case, the optical disk  12  is rotated until the recording linear speed of the radially-inward test recording area  29   a  becomes appropriate for recording.  
      Then, a predetermined signal is test-recorded in the radially-inward test recording area  29   a.    
      The test-recorded signal is read, and appropriate recording conditions are determined and set. Based on the appropriate conditions, information is recorded in the information recording area  29   d.    
      Subsequently, recording management information is recorded in the recording management area  29   b . The recording management information includes (i) address information used for the test recording and indicating a position in the radially-inward test recording area  29   a , and (ii) the recording conditions that have been set (including information regarding a used optical disk, a recording speed, recording power, a recording signal waveform).  
      In this manner, the information is recorded in the information recording layer  29 .  
      A description will now be given as to how information is recorded in the information recording area  29   d  of the first information recording layer  29  at a speed higher than the quadruple speed (e.g., at the 8× speed). In this case, the optical disk  12  is rotated until the recording linear speed of the radially-outward test recording area  29   g  becomes appropriate for recording.  
      Then, a predetermined signal is test-recorded in the radially-outward test recording area  29   g.    
      The test-recorded signal is read, and appropriate recording conditions are determined and set. Based on the appropriate conditions, information is recorded in the information recording area  29   d.    
      Subsequently, recording management information is recorded in the recording management area  29   b . The recording management information includes (i) address information used for the test recording and indicating a position in the radially-inward test recording area  29   g , and (ii) the recording conditions that have been set.  
      In this manner, the information is recorded in the information recording layer  29 .  
      A description will now be given as to how information is recorded in the information recording area  27   d  of the second information recording layer  27  at the standard speed or at a speed slower than the quadruple speed. In this case, the optical disk  12  is rotated until the recording linear speed of the radially-inward test recording area  27   a  becomes appropriate for recording.  
      Then, a predetermined signal is test-recorded in the radially-inward test recording area  27   a.    
      The test-recorded signal is read, and appropriate recording conditions are determined and set. Based on the appropriate conditions, information is recorded in the information recording area  27   d.    
      Subsequently, recording management information is recorded in the recording management area  29   b . The recording management information includes (i) address information used for the test recording and indicating a position in the radially-inward test recording area  27   a , and (ii) the recording conditions that have been set.  
      In this manner, the information is recorded in the information recording layer  27 .  
      A description will now be given as to how information is recorded in the information recording area  27   d  of the second information recording layer  27  at a speed faster than the quadruple speed (e.g., at the 8× speed). In this case, the optical disk  12  is rotated until the recording linear speed of the radially-outward test recording area  27   g  becomes appropriate for recording.  
      Then, a predetermined signal is test-recorded in the radially-outward test recording area  27   g.    
      The test-recorded signal is read, and appropriate recording conditions are determined and set. Based on the appropriate conditions, information is recorded in the information recording area  27   d.    
      Subsequently, recording management information is recorded in the recording management area  29   b . The recording management information includes (i) address information used for the test recording and indicating a position in the radially-outward test recording area  27   g , and (ii) the recording conditions that have been set.  
      In this manner, the information is recorded in the information recording layer  27 .  
      In the embodiment described above, information recording layer  29  includes radially-inward test recording area  29   a  and radially-outward test recording area  29   g , and information recording layer  27  includes radially-inward test recording area  27   a  and radially-outward test recording area  27   g . When information is recorded in information recording layer  29 , either radially-inward test recording area  29   a  or radially-outward test recording area  29   g  is used in accordance with the recording speed. Likewise, when information is recorded in information recording layer  27 , either radially-inward test recording area  27   a  or radially-outward test recording area  27   g  is used in accordance with the recording speed.  
      Because of the selective use of the radially-inward and radially-outward test recording areas, information can be recorded under the recording conditions suitable for the characteristics of the recording films constituting the information recording layers  29  and  27 . Hence, the recording conditions used for the information recording layers  29  and  27  can be optimized in accordance with the recording speeds. In addition, the recording management information, obtained when signals are test-recorded in the radially-inward test recording areas  29   a  and  27   a  and the radially-outward test recording areas  29   g  and  27   g , is recorded in the recording management area  29   b  of the first information recording layer  29 . Thus, the recording conditions corresponding to the information recording layers  29  and  27  and according with the recording speeds can be acquired by merely referring to the recording information stored in the recording management area  29   b . This is very convenient when information is additionally recorded on the write-once recording medium (DVD-R).  
      Information can be recorded in the information recording layers  29  and  27  as follows. That is, a radial position is predetermined on the optical disk  12 . Where information is recorded in areas that are inward of the radial position with respect to the predetermined radial position, a low-speed recording mode is selected. Where information is recorded in areas that are outward of the radial position, a high-speed recording mode is selected. In the low-speed recording mode, the radially-inward test recording areas  29   a  and  27   a  of the information recording layers  29  and  27  may be used. In the high-speed recording mode, the radially-outward test recording areas  29   g  and  27   g  of the information recording layers  29  and  27  may be used. In either recording mode, the recording management information is stored in the recording management area  29   b  of the first information recording layer  29 .  
       FIG. 2B  shows a modification of the PTP type optical disk  12  shown in  FIG. 2A . In  FIG. 2B , the same reference numerals as used in  FIG. 2A  denote corresponding or similar structural elements.  
      In the modification shown in  FIG. 2B , information recording layer  27  (the second information recording layer) includes a radially-inward test recoding area  27   a , a recording management area  27   b , a lead-in area  27   c , an information recording area  27   d , a lead-out area  27   e  and a radially-outward test recording area  27   g . These areas are sequentially formed from the innermost circumferential position of information recording layer  27  to the outermost circumferential position thereof.  
      In other words, information recording layers  29  and  27  have recording management areas  29   b  and  27   b , respectively.  
      When signals are test-recorded in the radially-inward and radially-outward test recording areas  29   a  and  29   g  of the first information recording layer  29 , recording management information obtained then is recorded in the recording management area  29   b  of the same information recording layer  29 .  
      Likewise, when signals are test-recorded in the radially-inward and radially-outward test recording areas  27   a  and  27   g  of the second information recording layer  27 , recording management information obtained then is recorded in the recording management area  27   b  of the same information recording layer  27 .  
      In the modification, each of the information recording layers  29  and  27  is provided with a recording management area  29   b  or  27   b  in which recording management information obtained at the time of test recording is stored. With this structure, radially-inward and radially-outward test recording areas  29   a  and  29   g  can be managed by using recording management area  29   b  provided for information recording layer  29 , and radially-inward and radially-outward test recording areas  27   a  and  27   g  can be managed by using recording management area  27   b  provided for information recording layer  27 .  
      Owing to this feature, recorded information can be managed based on the characteristics of the recording films constituting the information recording layers  29  and  27 .  
       FIG. 2C  shows a modification of the PTP type optical disk  12  shown in  FIG. 2B . In  FIG. 2C , the same reference numerals as used in  FIG. 2B  denote corresponding or similar structural elements.  
      In this modification, information recording layer  29  (the first information recording layer) includes a radially-inward test recoding area  29   a , a recording management area  29   b , a lead-in area  29   c , an information recording area  29   d , a lead-out area  29   e , a recording management area (RMA)  29   f  and a radially-outward test recording area  29   g . These areas are sequentially formed from the innermost circumferential position of information recording layer  29  to the outermost circumferential position thereof.  
      When signals are test-recorded in the radially-inward test recording area  29   a , the recording management information obtained then is recorded in recording management area  29   b.    
      When signals are test-recorded in the radially-outward test recording area  29   g , the recording management information obtained then is recorded in recording management area  29   f.    
      Information recording layer  27  (the second information recording layer) includes a radially-inward test recoding area  27   a , a recording management area  27   b , a lead-in area  27   c , an information recording area  27   d , a lead-out area  27   e , a recording management area (RMA)  27   f  and a radially-outward test recording area  27   g . These areas are sequentially formed from the innermost circumferential position of information recording layer  27  to the outermost circumferential position thereof.  
      When signals are test-recorded in the radially-inward test recording area  27   a , the recording management information obtained then is recorded in recording management area  27   b.    
      When signals are test-recorded in the radially-outward test recording area  27   g , the recording management information obtained then is recorded in recording management area  27   f.    
      In the modification shown in  FIG. 2C , each information recording layer  29  ( 27 ) has two recording management areas  29   b  ( 27   b ) and  29   f  ( 27   f ), one being used for the radially-inward test recording area  29   a  ( 27   a ) and the other being used for the radially-outward test recording area  29   g  ( 27   g ).  
      With this structure as well, recorded information can be managed based on the characteristics of the recording films constituting the information recording layers  29  and  27 .  
       FIGS. 3 and 4  are flowcharts illustrating the recording operation performed for the PTP type optical disk  12  described above.  
      When processing is started (S 1 ), it is determined whether the controller  23  requests the recording of information in the first information recording layer  29  (S 2 ).  
      When it is determined that the recording of information in the first information recording layer  29  is requested (S 2 -YES), the controller  23  determines whether the requested recording speed is slower than the quadruple speed, which is four times faster than the standard linear recording speed (S 3 ).  
      When it is determined that the requested recording speed is lower than the quadruple speed (S 3 -YES), then the controller  23  test-records signals in the radially-inward test recording area  29   a  of information recording layer  29  (S 4 ). The test-recorded signals are read (S 5 ), and a check is made to see whether the read signals are appropriate (S 6 ).  
      If the check shows that the read signals are not appropriate (S 6 -NO), recording conditions are changed, and the flow returns to Step S 4  (S 7 ).  
      When it is determined in Step S 3  that the requested recording speed is higher than the quadruple speed (which is four times faster than the standard linear recording speed) (S 3 -NO), then the controller  23  test-records signals in the radially-outward test recording area  29   g  of information recording layer  29  (S 8 ).  
      The test-recorded signals are read (S 9 ), and a check is made to see whether the read signals are appropriate (S 10 ).  
      If the check shows that the read signals are not appropriate (S 10 -NO), recording conditions are changed, and the flow returns to Step S 8  (S 11 ).  
      If the signals read in Step S 6  or Step S 10  are determined to be appropriate (S 6 -YES, S 10 -YES), the controller  23  records information in the information recording area  29   d  of the information recording layer (in this case, layer  29 ) at the requested recording speed (S 12 ). The information is recorded on the basis of the recording conditions under which the read signals are determined to be appropriate.  
      Thereafter, the controller  23  records recording management information in the recording management area  29   b  or  29   f  (S 13 ). The recording management information includes (i) address information used for the test recording and indicating a position in the test recording area  29   a  or  29   g ; and (ii) recording conditions that have been set.  
      In this manner, the processing is completed (S 14 ).  
      When it is determined that the recording of information in the first information recording layer  29  is not requested (S 2 -NO), the controller  23  determines that the recording of information in the second information recording layer  27  is requested. Based on this determination, the controller  23  determines whether the requested recording speed is slower than the quadruple speed (Si 5 ).  
      When it is determined that the requested recording speed is slower than the quadruple speed (S 15 -YES), then the controller  23  test-records signals in the radially-inward test recording area  27   a  of information recording layer  27  (S 16 ). The test-recorded signals are read (S 17 ), and a check is made to see whether the read signals are appropriate (S 18 ).  
      If the check shows that the read signals are not appropriate (S 18 -NO), recording conditions are changed, and the flow returns to Step S 16  (S 19 ).  
      When it is determined in Step S 15  that the requested recording speed is faster than the quadruple speed (S 15 -NO), then the controller  23  test-records signals in the radially-outward test recording area  27   g  of information recording layer  27  (S 20 ).  
      The test-recorded signals are read (S 21 ), and a check is made to see whether the read signals are appropriate (S 22 ).  
      If the check shows that the read signals are not appropriate (S 22 -NO), recording conditions are changed, and the flow returns to Step S 20  (S 23 ).  
      If the signals read in Step S 18  or Step S 22  are determined to be appropriate (S 18 -YES, S 22 -YES), the controller  23  records information in the information recording area  27   d  of the information recording layer (in this case, layer  27 ) at the requested recording speed (S 12 ). The information is recorded on the basis of the recording conditions under which the read signals are determined to be appropriate.  
      Thereafter, the controller  23  records recording management information in the recording management area  29   b ,  27   b  or  27   f  (S 13 ). The recording management information includes (i) address information used for the test recording and indicating a position in the test recording area  27   a  or  27   g ; and (ii) recording conditions that have been set.  
      In this manner, the processing is completed (Step S 14 ).  
       FIG. 5A  shows another example of the optical disk  12  described above.  
      The optical disk  12  comprises a circular substrate  31  made of polycarbonate. An information recording layer  32  made of a metallic material, an intermediate layer  33  made of a transparent material, an information recording layer  34  made of a semi-transparent material, and a cover layer  35  made of a transparent material are stacked on one side of the substrate in the order mentioned.  
      A laser beam emitted from the optical head  14  is incident on the cover layer  35 , as indicated by the arrow in  FIG. 5A , and is selectively focused on the two information recording layers  34  and  32 .  
      The optical disk  12  is an OTP (opposite track path) type. That is, information recording layer  34  (the first information recording layer), which is closer to the optical head  14  than information recording layer  32  is, starts the recording/reproduction of information from a radially-inward area to a radially-outward area, and information recording layer  32  (the second information recording layer), which is farther from the optical head  14  than information recording layer  34  is, starts the recording/reproduction of information from a radially-outward area to a radially-inward area.  
      To be more specific, information recording layer  34  (the first information recording layer) includes a radially-inward test recoding area (PCA)  34   a , a recording management area (RMA)  34   b , a lead-in area  34   c , an information recording area  34   d , a middle area  34   e , and a radially-outward test recording area (PCA)  34   g . These areas are sequentially formed from the innermost circumferential position of information recording layer  34  to the outermost circumferential position thereof.  
      Information recording layer  32  (the second information recording layer) includes a radially-outward test recoding area (PCA)  32   g , a middle area  32   e , an information recording area  32   d , a lead-out area  32   c , and a radially-inward test recording area (PCA)  32   a . These areas are sequentially formed from the outermost circumferential position of information recording layer  32  to the innermost circumferential position thereof.  
      Recording management information is recorded in the recording management area  34   b  of the information recording layer  34 . The recording management information includes (i) information obtained when signals are test-recorded in the radially-inward and radially-outward test recording areas  34   a  and  34   g  of the first information recording layer  34 , and (ii) information obtained when signals are test-recorded in the radially-inward and radially-outward test recording areas  32   a  and  32   g  of the second information recording layer  32 .  
       FIG. 5B  shows a modification of the OTP type optical disk  12  shown in  FIG. 5A . In  FIG. 5B , the same reference numerals as used in  FIG. 5A  denote corresponding or similar structural elements.  
      In this modification, information recording layer  32  (the second information recording layer) includes a radially-outward test recoding area  32   g , a middle area  32   e , an information recording area  32   d , a lead-out area  32   c , a recording management area (RMA)  32   b  and a radially-inward test recording area  32   a . These areas are sequentially formed from the outermost circumferential position of information recording layer  32  to the outermost circumferential position thereof.  
      In the modification, recording management areas  34   b  and  32   b  are provided for information recording layers  34  and  32 , respectively.  
      When signals are test-recorded in the radially-inward and radially-outward test recording areas  34   a  and  34   g  of the first information recording layer  34 , recording management information obtained then is recorded in the recording management area  34   b  of the same information recording layer  34 .  
      Likewise, when signals are test-recorded in the radially-inward and radially-outward test recording areas  32   a  and  32   g  of the second information recording layer  32 , recording management information obtained then is recorded in the recording management area  32   b  of the same information recording layer  32 .  
       FIG. 5C  shows a modification of the OTP type optical disk  12  shown in  FIG. 5B . In  FIG. 5C , the same reference numerals as used in  FIG. 5B  denote corresponding or similar structural elements.  
      In this modification, information recording layer  34  (the first information recording layer) includes a radially-inward test recoding area  34   a , a recording management area  34   b , a lead-in area  34   c , an information recording area  34   d , a middle area  34   e , a recording management area (RMA)  34   f  and a radially-outward test recording area  34   g . These areas are sequentially formed from the innermost circumferential position of information recording layer  34  to the outermost circumferential position thereof.  
      When signals are test-recorded in the radially-inward test recording area  34   a , the recording management information obtained then is recorded in recording management area  34   b . When signals are test-recorded in the radially-outward test recording area  34   g , the recording management information obtained then is recorded in recording management area  34   f.    
      Information recording layer  32  (the second information recording layer) includes a radially-inward test recoding area  32   g , a recording management area (RMA)  32   f , a middle area  32   e , an information recording area  32   d , a lead-out area  32   c , a recording management area  32   b  and a radially-outward test recording area  32   a . These areas are sequentially formed from the outermost circumferential position of information recording layer  32  to the innermost circumferential position thereof.  
      When signals are test-recorded in the radially-inward test recording area  32   a , the recording management information obtained then is recorded in recording management area  32   b . When signals are test-recorded in the radially-outward test recording area  32   g , the recording management information obtained then is recorded in recording management area  32   f.    
      In other words, each information recording layer  34  ( 32 ) has two recording management areas  34   b  ( 32   b ) and  34   f  ( 32   f ), one being used for the radially-inward test recording area  34   a  ( 32   a ) and the other being used for the radially-outward test recording area  34   g  ( 32   g ).  
      The radial positions of the middle areas  34   e  and  32   e  of the information recording layers  34  and  32  may be arbitrarily determined.  
       FIG. 6A  shows an optical disk wherein the middle areas  34   e  and  32   e  are more radially inward than those of the optical disk  12  shown in  FIG. 5A , as indicated by the broken lines.  
      In the case shown in  FIG. 6A , the middle areas  34   e  and  32   e  are at the same radial position of the optical disk  12 .  
      When signals are test-recorded in the radially-inward test recording area  32   a , the recording management information obtained then is recorded in recording management area  32   b . When signals are test-recorded in the radially-outward test recording area  32   g , the recording management information obtained then is recorded in recording management area  32   f.    
      The radial positions of the radially-outward test recording areas  34   g  and  32   g  are determined by the radial position of the middle areas  34   e  and  32   e.    
      Of the areas of the information recording layers  34  and  32 , those areas which are radially outward of the test recording layers  34   g  and  32   g  are not used for recording information.  
      As can be seen from the above, the radial positions of the middle areas  34   e  and  32   e  are determined depending upon whether all areas of the optical disk  12  are used for the recording/reproduction of information. To be more specific, the optical disk  12  warps less at the inner circumferential portions than at the outer circumferential portions. Therefore, using only the inner circumferential portions of the disk leads to reliable and stable recording and reproduction.  
      There may be a case where the outer circumferential portions of the optical disk  12  are not used for the recording/reproduction of information.  
       FIG. 6B  shows an optical disk wherein the middle areas  34   e  and  32   e  are more radially inward than those of the optical disk  12  shown in  FIG. 5B , as indicated by the broken lines. In the optical disk  12  shown in  FIG. 6B  as well, the middle areas  34   e  and  32   e  are at the same radial position of the optical disk  12 . The radial positions of the radially-outward test recording areas  34   g  and  32   g  are determined by the radial position of the middle areas  34   e  and  32   e.    
      Of the areas of the information recording layers  34  and  32 , those areas which are radially outward of the test recording layers  34   g  and  32   g  are not used for recording information.  
       FIG. 6C  shows an optical disk wherein the middle areas  34   e  and  32   e  are more radially inward than those of the optical disk  12  shown in  FIG. 5C , as indicated by the broken lines. In the optical disk  12  shown in  FIG. 6C  as well, the middle areas  34   e  and  32   e  are at the same radial position of the optical disk  12 . The radial positions of the radially-outward test recording areas  34   g  and  32   g  are determined by the radial position of the middle areas  34   e  and  32   e . Of the areas of the information recording layers  34  and  32 , those areas which are radially outward of the test recording layers  34   g  and  32   g  are not used for recording information.  
       FIGS. 7 and 8  are flowcharts illustrating how to determine the positions of the middle areas  34   e  and  32   e  in accordance with the amount of information to be recorded.  
      Referring to the flowcharts, processing is started (S 24 ), and when the recording of a user data file (information) is requested (S 25 ), the controller  23  checks whether or not the file size (i.e., the amount of information) of the user data file is smaller than the recording capacity of the recordable portion of the information recording area  34   d  of the first information recording layer  34  (S 26 ).  
      If the check shows that the file size is smaller than the recording capacity (S 26 -YES), the user data file is recorded in the information recording area  34   d , and the processing is ended (S 28 ).  
      If the check in step S 26  shows that the file size (i.e., the amount of information) of the user data file is smaller than the recording capacity of the recordable portion of the information recording area  34   d  of the first information recording layer  34  (S 26 -NO), the controller  23  determines whether the user data file should be recorded up to the maximal recording capacity of the recordable portion of the information recording area  34   d  of the first information recording layer  34  (S 29 ).  
      If the controller  23  determines that the user data file should be recorded up to the maximal recording capacity of the recordable portion of the information recording area  34   d  of the first information recording layer  34  (S 29 -YES), the user data file is recorded up to the maximum recording capacity (S 30 ).  
      Then, the controller  23  forms middle area  34   e  (recording management area  34   f , and radially-outward test recording area  34   g ) at the outermost circumferential position of the first information recording layer  34  (S 31 ).  
      Subsequently, the controller  23  forms middle area  32   e  (recording management area  32   f  and radially-outward test recording area  32   g ) at the outermost circumferential position of the second information recording layer  32  (S 32 ). Middle areas  34   e  and  32   e  are formed at the same radial position of the optical disk  12 .  
      Thereafter, the controller  23  records the remaining information of the user data file in the information recording area  32   d  of the second information recording layer  32  from the middle area  32   e  toward the read-out area  32   c  (S 33 ).  
      In this manner, the processing is ended (S 28 ).  
      If the controller  23  does not determine that the user data file should be recorded up to the maximal recording capacity of the recordable portion of the information recording area  34   d  of the first information recording layer  34  (S 29 -NO), the controller  23  divides the user data file into two pieces, one of which is to be recorded in the information recording area  34   d  of the first information recording layer  34  and the other of which is to be recorded in the information recording area  32   d  of the second information recording layer  32  (S 34 ).  
      Then, the controller  23  determines whether the outermost circumferential position of the data recorded in the information recording area  34   d  of the first information recording layer  34  is more radially outward from the outermost circumferential position of the data recorded in the information recording area  32   d  of the second information recording layer  32  by a predetermined distance (S 35 ).  
      If the controller  23  determines that the outermost circumferential position of the data recorded in the information recording area  34   d  of the first information recording layer  34  is not more radially outward (S 35 -NO), then the controller  23  changes the division ratio, and the flow returns to the processing of Step S 34  (S 36 ).  
      If the controller  23  determines in Step S 35  that the outermost circumferential position of the data recorded in the information recording area  34   d  of the first information recording layer  34  is more radially outward (S 35 -YES), the controller  23  records the user data file portion corresponding to the first information recording layer  34  in the information recording area  34   d  of the information recording layer  34  from the inner circumferential portions toward the outer circumferential portions (S 36 ).  
      After recording the user data file portion corresponding to the first information recording layer  34 , the controller  23  forms middle area  34   e  (recording management area  34   f  and radially-outward test recording area  34   g ) (S 37 ).  
      Then, the controller  23  forms middle area  32   e  (recording management area  32   f  and radially-outward test recording area  32   g ) in the second information recording layer  32  in such a manner that middle area  32   e  is at the same radial position as middle area  34   e  formed in the first information recording layer  34  (S 38 ).  
      Thereafter, the controller  23  records the remaining data of the user data file in the information recording area  32   d  of the second information recording layer  32  (S 39 ). The remaining data is recorded from the middle area ( 32   e ) side toward the lead-out area ( 32   c ) side.  
      In this manner, the processing is ended (S 28 ).  
      Where the middle areas  34   e  and  32   e  are formed radially inward, the recording management areas  34   f  and  32   f , the radially-outward test recording areas  34   g  and  32   g , etc. are also formed radially inward, accordingly.  
      In other words, where the middle areas  34   e  and  32   e  are located toward the center of the disk, the areas that are radially outward of the test recording areas  34   g  and  32   g  of the information recording layers  34  and  32  are unused areas, and information of any kind, including signals to be test-recorded, is not recorded in those areas.  
      Where the middle areas  34   g  and  32   g  are located toward the center of the disk, the radially-outward test recording areas  34   g  and  32   g  are controlled in such a way that they are not outward of the outermost limit position LA shown in  FIG. 6 . Data can be recorded in those areas of the information recording layers  34  and  32  which are radially inward of the outermost limit position LA.  
      The present invention is not limited to the embodiment and modifications described above. When the present invention is reduced to practice, its structural elements can be modified in various ways without departing from the spirit and scope of the invention. In addition, various inventions can be produced by properly combining the structural elements of the aforesaid embodiment. For example, some of the structural elements of the embodiment may be deleted. In addition, the structural elements of different embodiments may be combined.  
      Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.