Patent Publication Number: US-7911900-B2

Title: Write-once optical disc, and method and apparatus for recording management information on the write-once optical disc

Description:
This application claims the benefit of Patent Application No. 2003-062674 filed in Republic of Korea on Sep. 8, 2003; No. 2003-071127 filed in Republic of Korea on Oct. 13, 2003; and No. 2004-036073 filed in Republic of Korea on May 20, 2004. The entire contents of each of these applications are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a write-once optical disc, a method for recording management information of the write-once optical disc and a method and apparatus for recording and playing back the write-once optical disc. 
     2. Discussion of the Related Art 
     As an optical recording medium, optical discs on which high-capacity data can be recorded are widely being used. Among them, a new high-density optical recording medium (HD-DVD), for example, a Blu-ray disc, has been recently developed for recording and storing high-definition video data and high-quality audio data for a long term period. 
     The Blu-ray disc is the next generation HD-DVD technology and the next generation optical recording solution, and has an excellent capability to store data more than the existing DVDs. Recently, a technical specification of international standard for HD-DVD has been established. Related with this, various standards for a write-once Blu-ray disc (BD-WO) are being prepared following the standards for a rewritable Blu-ray disc (BD-RE). 
     Among the standards for the write-once Blu-ray disc (BD-WO), a method for recording management information has been discussed. This method involves a recording method of an information indicating a recording status of the disc, which is one of the characteristics of the write-once optical disc. 
     The information indicating the recording status of the disc allows a host or a user to easily find a recordable area on the write-once optical disc. In the existing write-once optical discs, this information is named variously. For example, in the case of CD series, this information is named a track information; in the case of DVD series, this information is named an RZone or a fragment. 
     Accordingly, there is an increasing demand for a method of efficiently recording the management information corresponding to the recording status of the high-density optical disc. And this method must be provided with the standardized information in order to secure mutual compatibility. In addition, there is a demand for a method of recording the management information on a disc, which can be applied to a write-once high-density optical disc performing defect management, as well as to the Blu-ray discs. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to an optical disc and a method and apparatus for recording disc management information, and particularly to a method and apparatus for efficiently managing the disc recording status information, which substantially obviate one or more problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a method and apparatus for defining types of sequential recording ranges (SRRs) and recording information on the SRRs in an SRR information (SRRI). 
     Another object of the present invention is to provide a method and apparatus for recording SRRI as disc recording status information that can be applied to a write-once optical disc on which physical defect management is performed, and to provide a method and apparatus for recovering a damaged SRRI from a write-once optical disc. 
     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
         FIG. 1  illustrates an overall structure of a write-once optical disc and a method for recording management information on the write-once optical disc according to the present invention; 
         FIGS. 2A through 2D  illustrate different types of opened SRRs of a write-once optical disc according to the present invention; 
         FIGS. 3A through 3E  illustrate different types of closed SRRs of a write-once optical disc according to the present invention; 
         FIG. 4A  illustrates an example of padding identification information when padding dummy data to a closed SRR of a write-once optical disc according to the present invention; 
         FIG. 4B  illustrates an example of padding identification information when padding dummy data to an opened SRR of a write-once optical disc according to the present invention; 
         FIG. 5  illustrates an overall structure of a write-once optical disc and a method for recording SRRI as disc management information according to the present invention; 
         FIG. 6A  illustrates a structure of an SRR entry list recorded in an SRRI according to the present invention; 
         FIG. 6B  illustrates an example of an SRR entry recorded in the SRR entry list of  FIG. 6A  according to the present invention; 
         FIG. 6C  illustrates an example of a structure of a list of opened SRRs field of an SRRI according to the present invention; 
         FIGS. 7A through 11B  illustrate a process of recording SRRI according to the disc recording status in a write-once optical disc according to the present invention; and 
         FIG. 12  is a flowchart illustrating a method of using SRRIs of a write-once optical disc when the latest SRRI is damaged according to an embodiment of the present invention; 
         FIGS. 13A and 13B  illustrate a method of restoring the latest SRRI in the write-once optical disc according to an embodiment of the present invention; and 
         FIG. 14  illustrates a recording/playback apparatus for a write-once optical disc according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     For the convenience of description, a write-once Blu-ray disc (BD-WO) is described for example. Most of the terminologies in this specification are widespread general words but there are some words selected and used by the inventor, the meaning of which will be described in detail in the corresponding description. The present invention should be understood not based on the simple meanings of the words but based on the specifically described meanings of the words, if such meanings have been discussed. 
     When a plurality of areas are formed on a disc and the areas are recorded sequentially, each of these areas is called a “sequential recording range” (SRR). An SRR is a unit of recording (sequential recording-unit) for sequential recording user data. An SRR has a size of one or more clusters. “SRR information” (SRRI) is a name for information identifying a recording status of a disc. SRRI is applied to a sequential recording mode of the disc and pertains to one or more SRRs. “Padding” means filling an unrecorded area in an SRR with dummy data or zeros at a user&#39;s request or under control of a recording/playback apparatus ( FIG. 12 ). “Session” is composed of one or more consecutive SRRs and identifies SRRs for compatibility to the specification only for playbacks. 
       FIG. 1  illustrates a structure of a write-once optical disc such as a BD-WO and a method for recording disc management information according to the present invention. The disc shown in  FIG. 1  has a single recording layer as an example. But the present invention is not limited to such, and is applicable to a disc having dual or multiple recording layers. 
     Referring to  FIG. 1 , the disc includes a lead-in area, a data area, and a lead-out area, all at the recording layer. The lead-in and lead-out areas have a plurality of disc (or defect) management areas (DMA 1 -DMA 4 ) for storing the same defect management information repeatedly. In the data area, an inner spare area ISA 0  and/or an outer spare area OSA 0  for replacing defective areas is provided. 
     It is known that a rewritable optical disc does not have or need a large DMA since its DMA can be written and erased repeatedly, even if the disc has the DMA of a limited size. This is not the case for a write-once optical disc such as a BD-WO. Since the write-once optical disc cannot be re-recorded on the area that was recorded once, the write-once optical disc needs and has a larger management area. To more effectively store management information, in the write-once optical disc the management information is temporarily stored in a temporary disc management area (TDMA). When the disc is ready to be finalized/closed, then the management information stored in a final/latest TDMA is transferred to a DMA for more permanent storage. 
     As shown in  FIG. 1 , the disc includes two TDMAs: TDMA 0  and TDMA 1 . The TDMA 0  is allocated to the lead-in area and has a fixed, non-variable size. The TDMA 1  is allocated to the outer spare area OSA 0  and has a size variable in accordance with the size of the spare area. The size P of the TDMA 1  may be, for example, P=(N*256)/4 clusters where N is a positive integer, which is about one fourth of the size of the entire outer spare area OSA 0 . 
     In each of the TDMA 0  and TDMA 1 , temporary defect list (TDFL) information and temporary disc definition structure (TDDS) information together (TDFL+TDDS) can be recorded in one recording-unit (e.g., one cluster in the case of a BD-WO), or SRRI and TDDS information together (SRRI+TDDS) can be recorded in one recording-unit as shown. The SRRI is recorded when a sequential recording mode is used, whereas SBM (space bit map) is used when a random recording mode is used. 
     At each update time, (TDFL+TDDS) or (SRRI+TDDS) are recorded to the TDMA in the size of one cluster. In the example of  FIG. 1 , a TDFL and a TDDS are recorded in one cluster of the TDMA 0 , an SRRI and a TDDS are recorded in the next cluster of the TDMA 0 , an SRRI and a TDDS are recorded in the next cluster of the TDMA 0 , and so on. 
     If a defective area occurs within the data area, a process of replacing it with the spare area is carried out. The TDFL is the information that manages this process as the defect list. In the case of a single layer disc, the TDFL is recorded with the size of 1 cluster to 4 clusters according to the size of the defect list. SRRI is information informing of whether a specific area of the disc is recorded or unrecorded. The SRRI can be widely used when the disc is of a consecutive recording type. That is, the SRRI can be usefully applied to the case where the disc is recorded in a sequential or incremental recording mode. In addition, the TDDS information is generally recorded on the last sector among the 32 sectors within one cluster of the management area. Information for general management and defect management of the disc is recorded as part of the TDDS information, and the TDDS information is generally always recorded last when the management information is updated within the TDMA. 
     The present invention relates to a method of generating and recording disc recording status information, which is applied to a new high density optical disc such as a BD-WO. In the present invention, SRRI is used as the disc recording status information, and various types of SRRs are defined as shown in  FIGS. 2A through 3E . The detailed structure of SRRI will be described referring to  FIGS. 5A through 6C . The present invention also defines and distinguishes different types of SRRs formed on the disc and uses them to record and playback the optical disc. A method of newly defining the types of the SRRs and creating information identifying the types of distinguished SRRs will be described in detail. 
       FIGS. 2A to 2D  illustrate different types of opened SRRs for the write-once optical disc (e.g., a BD-WO) according to the present invention. An opened SRR is an SRR in which data can be recorded. If the SRR is recordable, the SRR has “next writable address” (NWA). Accordingly, the opened SRR is the SRR having the NWA. The SRR that does not have the NWA and is not recordable is called a closed SRR. The closed SRR will be described referring to  FIGS. 3A through 3E . 
     More specifically,  FIG. 2A  shows an invisible SRR that is one type of an opened SRR. The invisible SRR is generally always formed on an outermost section of a disc or an initial black disc and means an unrecorded area. In other words, only a start address of the invisible SRR is defined and an end address of the invisible SRR means an end of user data. Since data is not yet recorded, “last recorded area” (LRA) has a zero value and the NWA has the same value as the start address of the invisible SRR. 
       FIG. 2B  shows an incomplete SRR that is another type of an opened SRR. The incomplete SRR is an SRR that is partially recorded in the invisible SRR of  FIG. 2A . In other words, only a start address of the incomplete SRR is defined and an end address of the incomplete SRR means an end of user data. However, since data is partially recorded in the incomplete SRR, the LRA of the incomplete SRR represents the last address at which normal user data is recorded and the NWA is the next address from the LRA of the incomplete SRR. That is, the NWA is the first PSN of the next available unrecorded cluster in the related SRR. 
     In the opened SRR, if the SRR is partially recorded, the relation between the LRA and the NWA will be now described in detail in relation with padding shown in  FIG. 2B . The enlarged view of the small dotted box portion in  FIG. 2B  is provided at a lower portion of the drawing. 
     In other words, LRA means the area in which user data are actually recorded. If the user data are recorded on some sectors in one cluster consisting of thirty-two sectors, the physical sector number (PSN) of the corresponding sector on which the user data are recorded is the LRA of the SRR as shown in  FIG. 2B . However, since the basic recording-unit of the Blu-ray disc is a cluster, NWA representing an additionally recordable area will be the PSN of a header sector of the following cluster. Accordingly, if data is recorded on some sectors of the cluster and recording is finished (i.e., the sequential recording is terminated), the remaining unrecorded sectors are padded with dummy data according to the present invention. For instance, the remaining unrecorded sectors of the cluster are padded with zeros as shown. If all the user data are recorded on even the last sector of the cluster, it is obvious that the padding described is not necessary. 
       FIG. 2C  shows an empty SRR that is yet another type of an opened SRR. The empty SRR is formed generally not at an outermost section of the disc, but is formed generally at a middle section to record data in contrast to the invisible SRR and the incomplete SRR of  FIGS. 2A and 2B . In other words, it is the case where a host or user makes an SRR, but does not yet record data on the SRR. Since the empty SRR has a start address and an end address but is not yet recorded, the LRA of the empty SRR has a “zero” value and the NWA has the same value as the start address of the empty SRR. 
       FIG. 2D  shows a partially recorded SRR that is yet another type of an opened SRR. The partially recorded SRR is an SRR that is partially recorded in the empty SRR of  FIG. 2C . Accordingly, the partially recorded SRR has a start address and an end address. Since data is partially recorded in the partially recorded SRR, the LRA of the partially recorded SRR represents the last address at which normal data is recorded and the NWA is the next writable address from the LRA. 
     In the opened SRR of  FIG. 2D , if the SRR is partially recorded, the enlarged view of the small dotted portion in  FIG. 2D  shows the relation between the LRA and NWA in relation with padding. The detailed description on this feature is omitted since it is the same as the description of  FIG. 2B . 
     Accordingly, referring to  FIGS. 2A through 2D , the opened SRRs of the present invention are classified into the unrecorded opened SRRs ( FIGS. 2A and 2C ) and the partially recorded opened SRRs ( FIGS. 2B and 2D ). The partially recorded opened SRRs ( FIGS. 2B and 2D ) can be classified into an opened SRR padded after the LRA, and an unpadded opened SRR. 
     According to the present invention, the total number of opened SRRs at any given time is limited to a predetermined number in the write-once optical disc due to a difficulty in management if the number of opened SRRs is large. For example, the total number of the opened SRRs on the disc may be sixteen at most in the BD-WO of the present invention. The information on the location and the number of the opened SRRs can be referred to using a “list of opened SRRs” field and a “number of opened SRRs” field in a header of the SRRI. The “list of opened SRRs” field and the “number of opened SRRs” field in the SRRI header will be described later when the SRRI structure is discussed referring to  FIGS. 5 through 6C . 
       FIGS. 3A to 3E  illustrate different types of closed SRRs for a write-once optical disc such as a BD-WO according to the present invention. A closed SRR is an SRR in which data (e.g., user data) cannot be recorded. If the SRR is not recordable, the SRR does not have a NWA. The closed SRR may be created because the SRR is fully recorded. Also, the closed SRR may be created because a user or host closes the SRR by a close command even though a recordable area remains in the SRR. 
     Particularly,  FIG. 3A  shows an empty SRR that is one type of a closed SRR. The empty SRR is an opened empty SRR ( FIG. 2C ) that is closed by a close command without any user-data recording thereto. Accordingly,  FIG. 3A  shows a closed empty SRR and  FIG. 2C  shows an opened empty SRR. 
       FIG. 3B  shows a partially recorded SRR that is another type of a closed SRR. The partially recorded SRR of  FIG. 3B  is the opened partially recorded SRR of  FIG. 2D  that is closed by a close command without any additional user-data recording thereto. Accordingly,  FIG. 3B  shows a closed partially recorded SRR and  FIG. 2D  shows an opened partially recorded SRR. 
       FIG. 3C  shows a complete SRR that is yet another type of a closed SRR. The complete SRR is an SRR in which user data are recorded fully in the SRR, or which is padded fully with dummy data. The complete SRR exists only among the closed SRRs. 
       FIG. 3D  shows a closed partially recorded SRR that is yet another type of a closed SRR. The partially recorded SRR of  FIG. 3D  is an SRR that is padded with dummy data in a recordable area after its LRA when closing the opened partially recorded SRR of  FIG. 2D . Herein, all the recordable areas or only some recordable areas (for example, one or more clusters) of the SRR after its LRA or NWA may be padded with dummy data used as padding data. In addition, when some areas are padded, a specific character code such as ASCII characters may be recorded as the padding data, instead of recording the dummy data so as to represent that the SRR is closed. In this case, the specific character code to be used as the padding data can be characters such as “CLSD” representing that a corresponding SRR is closed. 
       FIG. 3E  shows an empty SRR that is another type of a closed SRR. The empty SRR of  FIG. 3E  is an SRR that is padded with specific dummy data in a recordable area after its LRA and then closed when closing the opened empty SRR of  FIG. 2C . Herein, all the recordable areas or only some recordable area (for example, one or more clusters) of the SRR after its LRA or NWA may be padded with dummy data used as padding data. In addition, when some areas are padded, a specific character code such as ASCII characters may be recorded as the padding data, instead of recording the dummy data so as to represent that the SRR is closed. In this case, the specific character code to be used as the padding data can be characters such as “CLSD” representing that a corresponding SRR is closed. 
     If the closed SRRs of  FIGS. 3D and 3E  are fully padded with dummy data up to the end address, the closed SRRs of  FIGS. 3D and 3E  are the same SRRs as the complete SRR described above referring to  FIG. 3C . In other words, in the present invention, in determining the type of the closed SRR, the closed SRRs are defined to distinguish the case of closing the unrecorded remaining area(s) of the SRR without padding ( FIGS. 3A and 3B ) from the case of padding and closing the unrecorded remaining area(s) of the SRR ( FIGS. 3D and 3E ) when the opened SRR is changed into the closed SRR by a close command. 
     Additionally, in the present invention, when closing an SRR, it is possible to close the SRR without padding or to close the SRR after padding with specific padding data. It is considered that the Blu-ray disc is compatible to a disc only for playback in the same family though SRRs or if unrecorded areas are padded. A recording/playback apparatus (e.g., as shown in  FIG. 14 ) can selectively pad the disc so that the freedom of the design of the recording/playback apparatus is further ensured. When padding the disc, a recording/playback part (e.g., the component  10  in  FIG. 14 ) of the recording/playback apparatus can automatically record specific data, so that the component  10  receives specific data from a controller and can solve the time problem in the case of padding 
       FIGS. 4A and 4B  illustrate examples of padding identification information when padding dummy data respectively to a closed recorded SRR and an opened SRR of a write-once optical disc according to an embodiment of the present invention. The padding may be performed to an opened SRR when closing the opened SRR. But, it can also be performed to an opened SRR in response to a command not necessarily to close the SRR (e.g., in the cases of  FIGS. 2B and 2D  where padding is performed for terminating the sequential recording). That is,  FIG. 4A  is related to  FIG. 2B  or  2 D, and  FIG. 4B  is related to  FIG. 3D  or  3 E. 
     More specifically,  FIG. 4A  shows a case where the actual user data is recorded on only some areas of one cluster and the remaining areas of the cluster are padded with dummy data in the case of an opened SRR.  FIG. 4A  shows that padding identification information “Padding_flag” for distinguishing a sector in which actual user data is recorded from a sector padded with dummy data is set as control flag in the corresponding cluster. There exist 32 Padding_flags each corresponding to one of the 32 sectors of each cluster of an SRR. 
     As shown in  FIG. 4A , in this example, since sector  0 -sector  29  are the areas in which user data are recorded, the Padding_flag for each of these sectors is set to a certain value, e.g., “0b,” so as to indicate that no padding is present to the corresponding sector. On the other hand, since sector  30  and sector  31  are the areas padded with padding data, the Padding_flag for each of these sectors is set to a value such as “1b” so as to indicate that padding is present in the corresponding sectors. 
     In this example, the LRA represents the location (first PSN) of sector  29 . Accordingly, the optical recording/playback apparatus can decode a cluster including the LRA, read the Padding_flag corresponding to each of the sectors and then accurately recognize a sector padded with dummy data in the cluster. 
       FIG. 4B  shows that a specific cluster of the recordable areas in an SRR is fully padded with dummy data in the case of closing the SRR.  FIG. 4B  shows that padding identification information “Padding_flag” for distinguishing an SRR closed without padding from an SRR closed after padding is set as control flag in the corresponding cluster. 
     As shown in  FIG. 4B , in this example, since sector  0 -sector  31  are the areas padded fully with dummy data, the Padding_flag for each of these 32 sectors is set to a certain value such as “1b”, to indicate that the corresponding sectors are padded. Consequently, the optical recording/playback apparatus can decode a cluster having the padding identification information (Padding_flag) as describe above, read the Padding_flag corresponding to each of the sectors and then accurately recognize that all the sectors in the cluster are padded with dummy data. 
     In other words,  FIG. 4A  relates to padding for terminating the sequential recording on the disc whereas  FIG. 4B  relates to padding for closing an SRR.  FIG. 4A  shows that all the remaining sectors in the related cluster are padded with dummy data when the sequential recording is terminated. Each padding flag corresponds to each sector of the cluster, and is set to “1b” if the corresponding sector is padded. In the case of  FIG. 4A , padding occurs one sector at a time. On the other hand, in the case of  FIG. 4B , one or more clusters (one cluster at a time) are padded when closing the SRR. For one cluster padding, 32 padding flags corresponding to 32 sectors of that cluster are all set to “1b” to indicate the padding of that cluster as shown in  FIG. 4B . 
       FIGS. 5 through 6C  illustrate a structure of SRRI and information included in the SRRI according to the present invention. 
     Particularly,  FIG. 5  illustrates the overall structure of an SRRI. The SRRI pertains to one or more SRRs and is management information providing disc recording status. The SRRIs are recorded in TDMA(s) (e.g., the TDMA 0 ) in the optical disc structure of  FIGS. 1 and 5 . As shown in  FIG. 5 , each SRRI  60  in a TDMA is composed of three parts: a header  50 , a list of SRR entries  30  and an SRR list terminator  40 . The header  50  identifies the SRRI. The list of SRR entries  30  represents the recording status of each of the corresponding SRRs. The SRR list terminator  40  represents an end or termination of the SRRI. 
     The header  50  is located at a header in the SRRI and includes an “SRRI structure identifier” field  51 , a “List of opened SRRs” field  52 , a “Number of SRR entries” field  53  and a “Number of opened SRRs” field  54 , so that the overall SRR entry contents can be checked before the SRR entry list is read. Herein, the “SRRI structure identifier” field  51  identifies the SRRI. The “List of opened SRRs” field  52  informs of the location (identification) of the opened SRRs associated with the corresponding SRRI and will be described later in more detail referring to  FIG. 6C . The “Number of SRR entries” field  53  represents the total number of all SRRs associated with the SRRI  60 . The “Number of opened SRRs” field  54  represents the total number of opened SRRs. 
     After the header  50 , the list of SRR entries (or the SRR entry list)  50  is recorded in the SRRI. After the last SRR entry, the end of the SRRI is marked with the SRR list terminator  40 . The SRR list terminator  40  is meaningful as information indicating an end location of the corresponding SRRI if the SRRI has a variable size. 
     Accordingly, as disc management information, the SRRI is composed of the header  50 , the SRR entry list  30  and the SRR list terminator  40 . All such information is recorded in batch whenever it is updated. 
       FIG. 6A  illustrates an example of the SRR entry list  30  recorded in an SRRI according to the present invention. As shown in  FIG. 6A , the SRR entry list  30  is composed of one or more SRR entries  35 . Each of the SRR entries  35  carries information on one SRR (identified by the SRR number) on the disc, has a size of eight bytes (64 bits) and represents the recording status of the corresponding SRR. Each SRR entry  35  includes a status field  31  (Status  1 ) for storing the status of the corresponding SRR, a start address field  32  for storing a start address of the corresponding SRR, another status field  33  (Status  2 ) for storing the status of the corresponding SRR, and a last recorded address (LRA) field  34  for storing the LRA of the corresponding SRR (i.e., the end address of the user data stored in the SRR). Generally, the start address of the corresponding SRR in the start address field  32  is represented as a physical sector number (PSN). 
     According to an embodiment, the first 4 most significant bits (b 63 -b 60 ) among the 64 bits of the SRR entry  35  are allocated to the first status field  31 , the next 28 bits (b 59 -b 32 ) of the SRR entry  35  are allocated to the start address field  32 , the next 4 bits (b 31 -b 28 ) of the SRR entry  35  are allocated to the second status field  33 , and the last 28 bits (b 27 -b 0 ) of the SRR entry  35  are allocated to the LRA field  34 . 
       FIG. 6B  illustrates an example of the SRR entry  35  recorded in the SRR entry list  30  according to the present invention. The Status  1  field  31  is used to store information identifying whether or not any padding is performed in the corresponding SRR. The Status  2  field  33  is used to store information identifying whether or not the corresponding SRR is the start of a session. 
     As shown in  FIG. 6B , out of the 4 heading bits allocated to the Status  1  field  31 , one bit is used to store a padding identification information “P_flag” identifying whether or not the SRR has been padded with padding data. The other three bits of the 4 heading bits are reserved for any change of regulation. 
     It should be noted that the padding identification information “P_flag” recorded in the SRR entry is similar to the padding identification information “Padding_flag” described referring to  FIGS. 4A and 4B . However, they have different objects. If a specific SRR is finally padded, the P_flag is recorded in the SRR entry to directly represent that the corresponding SRR is a padded SRR. Accordingly, the optical recording/playback apparatus ( FIG. 12 ) can easily check whether or not the corresponding SRR is padded by examining the P_flag recorded as management information in the SRR entry. After that, the optical recording/playback apparatus decodes the corresponding cluster (SRR) described above referring to  FIGS. 4A and 4B  and reads from the cluster the value of the Padding_flag corresponding to each sector of the SRR, so that the optical recording/playback apparatus is able to determine how much of the SRR is padded after its LRA. 
     In the example of  FIG. 6B , the first bit ( 31   a ) of the Status  1  field  31  carries the P-flag and the remaining 3 bits ( 31   b ) of the field  31  are reserved. If P_flag=1b, it means that the corresponding SRR is a padded SRR (i.e., the SRR has at least some portion that is padded with padding data). If P_flag=0b, it means that the corresponding SRR is an unpadded SRR. 
     The Status  2  field  33 , which is allocated with 4 bits, carries information on whether or not the corresponding SRR is the session start SRR. One bit of the four-bit field  33  carries a session identification information “S_flag” identifying whether or not the corresponding SRR is a start SRR of a session. The other three bits of the field  33  are reserved for any change of regulation. In the example, the first bit ( 33   a ) of the four-bit field  33  stores the S-flag and the remaining 3 bits. ( 33   b ) are reserved. If S_flag=1b, it means that the corresponding SRR is a start SRR of a session. If S_flag=0b, it means that the corresponding SRR is not a start SRR of a session. 
     One reason for identifying a start of a session through the S_flag is to provide compatibility with existing disc structures such as DVDs that allocate additional area (for example, border-in/border-out) to distinguish sessions. However, allocation of the additional area reduces the entire recording capacity of the disc. As such, the present invention overcomes this limitation by providing the session identification information (S_flag) in the SRR entry  35 . Accordingly, the session structure of the entire disc can be easily recognized using the session identification information S_flag in the SRR entry  35  without having to allocate additional areas to store such session distinguishing information. 
     For the convenience of description of the present invention, the P_flag and the S_flag are depicted as separate status information stored in separate status fields of an SRR entry, but they can be stored together in one status field of the SRR entry. 
     The LRA field  34  of the SRR entry  35  is a field for recording an end address (LRA) of user data recorded in the corresponding SRR and stores an end address of the user data (excluding any padding data) recorded in the corresponding SRR 
       FIG. 6C  illustrates a detailed structure of the “List of opened SRRs” field  52  of the SRRI in  FIG. 5  according to an embodiment of the present invention. The information stored in the field  52  is used to determine the location/identification of each opened SRR. As shown in  FIG. 6C , one or more opened SRR numbers are recoded in the “List of opened SRRs” field  52  as location information of the opened SRRs. Two bytes are allocated to record an opened SRR number identifying a particular SRR. 
     In the present invention, if there are at most sixteen opened SRRs on the disc, the location (identification) of the corresponding opened SRRs (and thus the opened SRR entries) is recorded through each opened SRR number. Accordingly, when loading an optical disc having the disc structure of the present invention, the recording/playback apparatus can determine the location of recordable areas (NWA) of the disc based on the opened SRR information of the present invention. In other words, the location of the opened SRR on the current disc should be known to record data. Since the information identifying whether a corresponding SRR is an opened SRR or a closed SRR is not provided specifically in the SRR entry, the identification/location of the opened SRR is recorded in the header of the SRRI and can be accessed easily, so that the optical recording/playback apparatus is able to easily read the SRR entry associated with the identified opened SRR. 
     Accordingly, only the SRR having the SRR number recorded on the “List of opened SRRs” field  52  is additionally recordable as an opened SRR. After that, if the SRR is changed into a closed SRR, the SRR number of the closed SRR is removed from the “List of opened SRRs” field  52  so that it is possible to easily distinguish the opened SRR from the closed SRR. 
     A method for updating the SRRI representing the disc recording status according to the present invention will be now described. Particularly, a method of opening and closing SRRs and sessions, padding an SRR with dummy data and recording SRRIs will be described referring to  FIGS. 7A-11B . 
       FIGS. 7A through 11B  illustrate sequentially a method of recording SRRI according to the disc recording status in the write-once optical disc of the present invention. More specifically,  FIGS. 7A through 11B  show sequentially how the different types of SRRs (shown in  FIGS. 2A through 3E ) on the disc are created and how to record the SRRI using the sequential steps performed according a time flow. These methods are implemented on the write-once optical disc such as BD-WO having the SRR, the SRRI and the disc structure as discussed herein in connection with  FIGS. 1-6C . 
       FIG. 7A  shows Step  1  in which the entire area of the disc is recordable as an initial black disc and a portion designated by a thick arrow indicates the NWA location. The start location of the disc is the NWA. Herein, only one SRR (SRR # 1 ) exists on the disc. This is the invisible SRR shown in  FIG. 2A . Accordingly, a session is in the initial state of the disc wherein only one opened session # 1  exists. The disc is a blank disc and the SRRI is not yet recorded on the disc. A session is an upper-level recording-unit compared to the lower-level recording-unit such as an SRR, and includes at least one SRR. A plurality of sessions can be recorded on the disc and such a disc is called a multi-session disc. 
       FIG. 7B  shows Step  2  in which data (e.g., user data) are partially recorded on the blank disc of  FIG. 7A , but the session # 1  is not yet closed. Herein, only one SRR (SRR # 1 ) exists on the disc, which is the incomplete SRR shown in  FIG. 2B . The session # 1  is maintained as the opened session. As shown in  FIG. 7B , the user data is recorded in a portion of the incomplete SRR # 1  and an unrecorded portion (e.g., sector(s)) of the SRR # 1  (cluster) is padded with dummy data. As described above, the padded sector of the SRR is indicated with “Padding_flag=1b” which is recorded in a designated area of the cluster, e.g., within the padded sector of the cluster/SRR # 1 . 
       FIG. 7C  illustrates a process of recording an SRRI in the management area of the disc when the disc is in the state of  FIG. 7B . For the convenience of explanation, only certain portions among all the different components of the disc structure and SRRI structure shown in  FIGS. 1 and 5  are shown. For instance, although the (SRRI+TDDS) or (TDFL+TDDS) are recorded in each cluster of the TDMA such as the TDMA 0  of the disc as discussed above, only the SRRI is shown in the TDMA 0  of  FIG. 7C , and the TDFL and/or TDDS is omitted for the sake of clarity. Further, only the “List of opened SRRs” field  52  and the “List of SRR entries” field  30  among the different fields of the SRRI shown in  FIG. 5  are shown. 
     The disc recording status of  FIG. 7C  is the case where only one opened SRR (SRR # 1 ) is present in all the disc area as in  FIG. 7B . As shown in  FIG. 7C , when the incomplete SRR # 1  is formed without closing the session as in  FIG. 7B , the SRRI # 1  ( 60   a ) pertaining to the SRR # 1  is generated and recorded in the TDMA 0 . In the SRRI # 1  ( 60   a ), the SRR number (SRR # 1 ) of the opened SRR # 1  is recorded in its “List of opened SRRs” field  52   a . In the “List of SRR entries” field  30   a  of the SRRI # 1  ( 60   a ), only one SRR entry  35   a  pertaining to the SRR # 1  is present. The SRR entry  35   a  (or SRR entries  35   b - 35   p  discussed later) has the SRR entry structure of  FIGS. 6A and 6B  discussed above. 
     In the SRR entry  35   a , since some portions of the SRR # 1  are padded finally, the P_flag is set to “1b” as the status information of the corresponding SRR # 1 . Since the SRR # 1  is the start SRR of the opened session # 1 , the S_flag is set to “1b” as the status information of the corresponding SRR # 1 . 
       FIG. 8A  shows Step  3  in which a session close command is received and executed at Step  2  of  FIG. 7B . In response to the session close command, the area on which user data is recorded is separated into an independent closed SRR and a new session is created at the area following the user data recorded area. For instance, as shown in  FIG. 8A , the portion of the area that is recorded fully with the user data at Step  2  becomes the complete SRR # 1  (closed SRR) which in turn forms the closed session # 1 . In addition, the unrecorded area becomes an invisible SRR # 2  (opened SRR) which in turn forms an opened session # 2  at the same time. 
       FIG. 8B  illustrates a process of recording the disc recording status (SRRI) as it pertains to the disc state as of  FIG. 8A . Since the SRRI is a second recorded SRRI, this SRRI is named SRRI # 2  ( 60   b ). The SRRI # 2  ( 60   b ) is recorded next to the SRRI # 1  ( 60   a ) in the TDMA 0 . For recording the status of the disc of  FIG. 8A , since the entire area of the disc has only one opened SRR (SRR # 2 ) and only one closed SRR (SRR # 1 ), the SRR number of the opened SRR # 2  is recorded in the “List of opened SRRs” field  52   b  of the SRRI # 2 , and information on the SRRs # 1  and # 2  is recorded in the “List of SRR entries” field  30   b  of the SRRI # 2  respectively as SRR entries  35   b  and  35   c . The SRR entry (e.g.,  35   b ) shadowed in  FIG. 8B  (and in other figures) indicates that it is a closed SRR entry. Accordingly, since user data is not yet recorded in the newly created SRR # 2 , the P_flag of the SRR # 2  entry ( 35   c ) is set to “0b”. Since the SRR # 2  is the start SRR of the opened session # 2 , the S_flag of the SRR # 2  entry ( 35   c ) is set to “1b”. 
       FIG. 9A  shows Step  4  in which two opened SRRs are additionally reserved to newly record data when the disc is in the state of  FIG. 8A . Accordingly, the newly created opened SRRs are opened empty SRRs # 2  and # 3  and have NWAs indicated by thick arrows. As a result, the opened session # 2  is composed of the empty SRRs # 2  and # 3  and an invisible SRR # 4 . 
       FIG. 9B  illustrates a process of recording the disc recording status (SRRI) as it pertains to the disc state as of  FIG. 9A . Since the SRRI is a third recorded SRRI, the SRRI is named SRRI # 3  ( 60   c ). The SRRI # 3  ( 60   c ) is recorded adjacent to the SRRI # 2  ( 60   b ) in the TDMA 0 . For recording the status of the disc of  FIG. 9A , since the entire area of the disc has three opened SRRs (SRRs # 2 , # 3  and # 4 ) and one closed SRR (SRR # 1 ), the SRR numbers (SRRs # 2 , # 3  and # 4 ) of the opened SRRs are recorded in the “List of opened SRRs” field  52   c  of the SRRI # 3 . Information on all four SRRs (SRRs # 1 -# 4 ) is recorded in the “List of SRR entries” field  30   c  of the SRRI # 3  respectively as SRR entries  35   d - 35   g.    
     Accordingly, since information on the newly created SRR # 2 , # 3  and # 4  is recorded in the SRRI # 3  ( 60   c ) and user data is not yet recorded on the SRRs # 2 , # 3  and # 4 , the P_flags of the corresponding SRR entries  35   e,    35   f ,  35   g  are set to “1b”. However, since the SRRs # 3  and # 4  are not the start SRR of the opened session # 2 , but the SRR # 2  is the session start SRR, the S_flags of the SRR # 2  entry  35   e , the SRR # 3  entry  35   f  and the SRR # 4  entry  35   g  are set respectively to “1b”, “0b” and “0b”. 
       FIG. 10A  shows Step  5  in which user data is recorded in the empty SRR # 2  and in the invisible SRR # 4  of  FIG. 9A . Accordingly, the first empty SRR # 2  is changed into a partially recorded SRR # 2 , and the invisible SRR # 4  is changed into an incomplete SRR # 4 , but the opened empty SRR # 3  is not changed. The SRR # 2  is recorded with user data without padding. The SRR # 4  is recorded with user data and is also padded with padding data. In the padded sector of the SRR # 4 , the Padding_flag is set to “1b”. 
       FIG. 10B  illustrates a process of recording the disc recording status (SRRI) as it pertains to the disc state as of  FIG. 10A . Since the SRRI is a fourth recorded SRRI, the SRRI is named SRRI # 4  ( 60   d ). The SRRI # 4  ( 60   d ) is recorded next to the SRRI # 3  ( 60   c ). For recording the status of the disc of  FIG. 10A , since the entire area of the disc has three opened SRRs (SRRs # 2 -# 4 ) and one closed SRR (SRR # 1 ), the SRR numbers of the opened SRRs (SRRs # 2 -# 4 ) are recorded in the “List of opened SRRs” field  52   d  of the SRRI # 4  ( 60   d ). Information on all four SRRs (SRRs # 1 -# 4 ) is recorded in the “List of SRR entries” field  30   d  of the SRRI # 4  ( 60   d ) respectively as SRR entries  35   h - 35   k.    
     At this step, the number of the SRR entries and the location of the opened SRRs are the same as those shown in  FIG. 9B , but since user data is recorded on a specific opened SRR, the LRA of the recorded opened SRR entry is changed and the value of the P_flag is also changed. In other words, information on the recorded SRRs # 2  and # 4  is updated. Since the SRR # 2  is recorded with user data without padding, the P_flag of the SRR # 2  entry  35   i  is maintained to be “0b”. Since the SRR # 4  is recorded with user data and is padded, the P_flag of the SRR # 4  entry  35   k  is changed to be “1b”. 
       FIG. 11A  shows Step  6  in which a session close command is received and executed when the disc is in the state of  FIG. 10A . As shown in  FIG. 11A , the additionally recordable portion of the opened SRR or a part of the additionally recordable portion of the opened SRR is padded with dummy data before the opened SRR is closed. As described above, the padding operation is an optional feature. In addition, when the padding is performed, specific data (for example, “CLSD” as character code) may be recordable as the padding data as described above. 
     The SRRs # 2 , # 3  and # 4  that were previously opened SRRs are changed into a closed partially recorded SRR # 2 , a closed empty SRR # 3  and a complete SRR # 4 , which in turn form the closed session # 2 . In the SRRs # 2  and # 3 , an additionally recordable area remains but is changed into a closed SRR by a close command. Herein, some portion is alternatively padded with dummy data. Accordingly, all the sectors in the cluster/SRR (e.g.  FIG. 4B ) padded with dummy data are set with Padding_flag=1b. However, even in this case, LRA recorded in the SRR entry means an end location where the user data are actually recorded. Dummy data portion does not affect the determination of the LRA location as described above. A remaining outermost SRR # 5  is an invisible SRR # 5 , which in turn forms a new opened session # 3 . 
       FIG. 11B  illustrates a process of recording the disc recording status (SRRI) as it pertains to the disc state as of  FIG. 11A . Since the SRRI is a fifth recorded SRRI in the management area, the SRRI is named SRRI # 5  ( 60   e ). The SRRI # 5  ( 60   e ) is recorded next to the SRRI # 5  ( 60   d ) in the TDMA 0 . For recording the status of the disc of  FIG. 11A , since the entire area of the disc has one opened SRR (SRR # 5 ) and four closed SRRs (SRRs # 1 -# 4 ), the SRR number of the opened SRR (SRR # 5 ) is recorded in the “List of opened SRRs” field  52   e  of the SRRI # 5 , and all the previous opened SRR numbers (for example, SRRs # 2 , # 3  and # 4  in  FIG. 10B ) recorded in the SRRI # 4  are removed from the current opened SRR list  52   e . Removal of the SRRs from the “List of opened SRRs” field means that such SRRs are closed. Information on all five SRRs (SRRs # 1 -# 5 ) is recorded in the “List of SRR entries” field  30   e  of the SRRI # 5  respectively as SRR entries  35   l - 35   p.    
     Since the SRRs # 2  and # 3  are padded with dummy data in response to the close command, the P_flags of the SRR # 2  entry  35   m  and the SRR # 3  entry  35   n  are changed to “1b” to indicate that at least a part of the corresponding SRR is padded with padding data. Since the LRA of an SRR entry is an end location where the user data is actually recorded, the LRAs of the SRRs # 2 -# 4  have the same value as the previous LRAs recorded in the SRRI # 4  ( 60   d ). In addition, since user data is not yet recorded on the newly created invisible SRR # 5 , the P_flag of the SRR # 5  entry  35   p  is set to be “0b”. Since the SRR # 5  is a start SRR of the new session # 3 , the S_flag of the SRR # 5  entry  35   p  is set to be “1b”. 
     As can be seen through  FIGS. 7A to 11B , SRRI is the information indicating the recording status of the current disc. When loading the optical disc of the present invention into the recording/playback apparatus, the recording/playback apparatus should check the latest SRRI (SRRI # 5 , in the above example) finally recorded in the management area. Since only the latest SRRI correctly indicates the final recording status of the disc, it is possible to check the location of the additionally recorded SRR. 
     However, when the power is suddenly turned off while using the disc or the disc is damaged, the latest SRRI of the disc may not be read out correctly. At this time, the final recording status need to be reconstructed using the latest SRRI among the non-damaged SRRIs. According to the present invention, the SRR is padded in the padding operation when the SRR is to be closed, and this padding information can be used to reconstruct the final recording status of the disc even when the latest SRRI on the disc is at a damaged condition. Through it, it is possible to recover the latest SRRI and the current recording status of the disc. 
       FIGS. 12 ,  13 A and  13 B illustrate a method of recording data on a write-once optical disc according to the present invention. This method estimates the final recording status of the disc, recovers the latest SRRI of the disc even when the latest SRRI is damaged. The recording/playing back can be performed using the final recording status obtained from the latest SRRI. 
     When the corresponding SRRI is judged as a defective area and the recorded information is not reliable, the SRRI is said to be damaged. If the latest SRRI is damaged, it means that the final recording status of the disc cannot be obtained from the latest SRRI. Therefore, the recordable location of the disc cannot be known. In the worst case, the disc itself cannot be used any more. 
     The present invention provides the method of correctly recovering the final recording status of the disc when the latest SRRI is damaged. Particularly,  FIG. 12  is a flowchart illustrating a method of recovering the final recording status of a write-once optical disc such as a BD-WO and performing the recording/playback operation on the disc according to an embodiment of the present invention. The disc contains the disc structure and the SRRI structure as discussed above. 
     Referring to  FIG. 12 , if the disc is loaded in an optical recording/playback apparatus such one shown in  FIG. 14 , the latest SRRI recorded within the management area (e.g., the TDMA 0 ) is read out. Then, it is checked whether or not the read SRRI is damaged (S 10 ). 
     If the latest SRRI is not damaged, the final disc recording status is obtained from the latest SRRI (S 21 ). Then using the latest SRRI, the recording is performed to only the additionally recordable area and/or the playback operation is performed to the already recorded area (S 22 ). The information on such areas is obtained from the latest SRRI. 
     On the other hand, if the step S 10  determines that the latest SRRI is damaged, the latest SRRI among the non-damaged SRRI(s) is determined (S 31 ). Then this latest non-damaged SRRI is read out (S 32 ). The damaged SRRI can be recovered using the latest non-damaged SRRI and the actual recording status of the disc (S 33 ). Step S 33  may be an optional step. The recording is performed to the additionally recorded area and/or the playback operation is performed to the already recorded area (S 34 ). Information on such areas can be determined from the latest non-damaged SRRI and/or the actual recording status of the disc. After the recording/playback step S 34 , the newly changed recording status may be recorded as a new SRRI in the management area. 
       FIGS. 13A and 13B  illustrates an example of the step S 33  in  FIG. 12  of recovering the final recording status when the latest SRRI (SRRI # 5  in the example of  FIG. 11B ) is damaged. For the convenience of explanation, the SRRI recording method of  FIGS. 7A to 11B  will be described as an example. 
     As shown in  FIG. 13A , if the SRRIs are in the normal status, the SRRI # 5  ( 60   e ) becomes the latest SRRI of the disc. However, if the SRRI # 5  is damaged, the recording/playback apparatus reads the latest SRRI among the non-damaged SRRIs. In the example, the SRRI # 4  ( 60   d ) is the latest SRRI among the non-damaged SRRIs # 1 -# 4 . 
     The actual recording status associated with Step  6  in  FIG. 11A  can be determined from the SRRI # 5  ( 60   e ) which is written as indicated in  FIG. 11B . However, since the SRRI # 5  ( 60   e ) is damaged, the latest SRR information that can be checked by the recording/playback apparatus is the SRRI # 4  ( 60   d ). But the SRRI # 4  does not necessarily carry the final recording status of the disc since the SRRI # 5  carries this information. Then, in order to recover the final recording status of the disc without using the SRRI # 5 , the SRRI # 4  and the actual final recording status of the disc need to be compared. This can be accomplished as follows. 
     The recording/playback apparatus (e.g.,  FIG. 14 ) checks the location of the opened SRR(s) and the associated LRA information from the SRRI # 4 . In the example of  FIG. 13A , it is determined from the “List of opened SRRs” field  52   d  of the SRRI # 4  ( 60   d ) that there are three opened SRRs # 2 , # 3  and # 4 . Then by accessing the LRA field of these SRR entries corresponding to these opened SRRs from the “List of SRR entries” field  30   d  of the SRRI # 4  ( 60   d ), the LRAs are obtained and used to verify whether the corresponding SRR is truly an opened SRR. In this regard, only the opened SRR(s) identified in the field  52   d  of the SRRI # 4  ( 60   d ) are examined. The location recorded with the closed SRR(s) may not be verified. Once an opened SRR is changed to a closed SRR, the closed SRR cannot be changed back to an opened SRR. As a result, the recovery of the final SRR information is possible by checking whether each of the opened SRR(s) is changed to the closed SRR. 
     In the case of the SRRs # 2  and # 3  that are identified as the opened SRRs in the field  52   d  of the SRRI # 4  ( 60   d ), each of the SRRs # 2  and # 3  is examined to determine whether or not predetermined padding data (e.g., dummy data) are recorded after its LRA (identified in the LRA field of the entry), as can be seen from  FIG. 11A  (actual final disc recording status). If the padding is detected, then the recording/playback apparatus determines that the corresponding opened SRR is changed to a closed SRR. 
     In the case of the SRR # 4  that is recognized as the opened SRR from the field  52   d  of the SRRI # 4 , the recording/playback apparatus examines the SRR # 4  to determine whether or not the padding data (e.g., dummy data) are presented after its LRA location in  FIG. 11A  (actual final disc recording status). The SRR # 4  can be analyzed as the opened SRR in the actual final disc recording status. Also, it can be seen that an area after the LRA location of the SRR # 4  is recordable, i.e., this area is the NWA. Then in the recording/playback apparatus, the already recorded area of the original SRR # 4  is determined to a closed SRR (new closed SRR # 4 ) and only the recordable area of the original SRR # 4  is analyzed as the opened SRR (new SRR # 5 ). Thus the contents of the damaged SRRI # 5  can be reconstructed by using the above analysis results. Moreover, since the information necessary to perform the recording operation by the recording/playback apparatus is the additionally recordable position information (NWA), the NWA location in association with the old and new SRR # 4  is not changed and thus can be used by the recording/playback apparatus. 
       FIG. 13B  illustrates a result of the recovery of the latest SRRI # 5  by the process of  FIG. 13A  as discussed above. This result accords with the final recording status of the actual disc. Accordingly, the recording/playback apparatus again records the selectively recovered latest SRRI # 5  within the management area (at this time, as the SRRI # 6  ( 60   f )), or performs the recording to only the additionally recordable area. The SRRI # 6  ( 60   f ) includes the “List of opened SRRs” field  52   f  identifying the SRR # 5 , and the “List of SRR entries” field  30   f  containing SRR entries  35   q - 35   u  corresponding respectively to the SRRs # 1 -# 5 . Also, even if the recovered SRRI # 5  is not recorded as the SRRI # 6 , data recording is performed from the recovered NWA information and the recording status as changed by the data recording to the recovered NWA is recorded as a new SRRI # 6 . 
       FIG. 14  illustrates an optical disc recording/playback apparatus according to the present invention. This apparatus or other suitable apparatus or system can be used to implement the disc and/or SRRI structures and methods of the present invention discussed herein. 
     Referring to  FIG. 14 , the optical disc recording/playback apparatus includes a recording/playback unit  10  for recording and/or reproducing data to/from the optical disc and a controller  20  for controlling the recording/playback unit  10 . All the elements of the recording/playback apparatus are operatively coupled. The controller  20  transmits a command for recording and/or reproducing to/from a special recording area such as an SRR/session on the disc, to the recording/playback unit  10 . The recording/playback unit  10  records and/or reproduces data to/from the disc according to the commands of the controller  20 . 
     The recording/playback unit  10  includes an interface unit  12 , a pick-up unit  11 , a data processor  13 , a servo unit  14 , a memory  15  and a microcomputer  16 . The interface unit  12  communicates with external devices such as the controller  20 . The pick-up unit  11  records or reproduces data to/from the optical disc directly. The data processor  13  receives a reproduction signal from the pick-up unit  11 , restores a preferred signal, modulates a signal proper to the optical disc, and transmits the signal. The servo unit  14  controls the pick-up unit  11  to read the signal from the optical disc or to record the signal to the optical disc. The memory  15  stores temporarily data and various information including management information as discussed herein. The microcomputer  16  controls the components of the recording/playback unit  10 . Since the recording/playback apparatus shown in  FIG. 14  can selectively perform a padding operation, a designer can more freely design the recording/playback apparatus. The recording/playback unit  10  can automatically store specific data during a padding operation. 
     The method of recording and playing back data on an optical disc is classified into two kinds. The first one is the case of  FIGS. 4A through 11B , which involves the method of completely recording data on an opened SRR, forcedly padding the remaining sector(s) in the cluster including the LRA, and recording information identifying whether or not padding has been performed to the remaining sector(s), or determining whether or not to pad the cluster and recording padding identification information according to the padding when closing an SRR. 
     The second one is the method of effectively recovering a damaged SRRI using the padding information of  FIGS. 12-13B . When closing an SRR, padding the SRR is optionally performed. However, if the padding is performed to the SRR and then the SRR is closed, then this padding information can be used advantageously to recover data. 
     The first recording/playback method of the optical disc according to an embodiment of the present invention will be described in detail. When the optical disc such as a BD-WO is loaded into the recording/playback apparatus such as the one shown in  FIG. 12 , the latest SRRI is read as the latest disc management information recorded in a TDMA. Furthermore, the SRRI header and the SRR entry(ies) recorded in the latest SRRI are read and temporarily stored in the memory  15  of the recording/playback unit  10 . 
     The stored SRRI represents the latest disc recording status. The opened SRR(s) can be identified through the SRRI header information. Through the SRR entry(ies), data can be recorded in the entire area of the disc or the existence and location of the non-recording status and opened session can be checked. Also, it can be identified whether or not the SRR has been padded with padding data. All such information can be used when the optical disc is recorded and played back. 
     Then, data (e.g., user data) is recorded on a specific opened SRR. When the data is completely recorded in the opened SRR, the unrecorded sector(s) in the cluster including the LRA is padded with dummy data (e.g., for stability and robust reasons) and the padding identification information Padding_flag is set to “1b”. For each of the padded sectors, Padding_flag corresponding to each sector is set to “1b”. If the sector is not padded, then the corresponding Padding_flag is set to “0b”. Also, when the SRR entry in the SRRI is updated, the SRR status information P_flag is set to “1b” to indicate that the corresponding SRR has at least some part that is padded. 
     Additionally, even in the case where the SRR is closed by a close command of the controller  20 , the microcomputer  16  can select whether a recordable area (for example, one cluster) closed after padding or without padding. In the above case, a designer can design so that the recording/playback unit  10  automatically pads the SRR with padding data and closes the SRR unconditionally without a padding command from the controller  20 . The above function is called “automatic padding function” by the recording/playback unit  10 . The automatic padding function is more advantageous to reduce padding operation time, compared to the case where the recording/playback unit  10  receives dummy data by a padding command and pads the SRR thereafter. 
     In addition, if the SRR status is changed by padding as described above, the Padding_flag is set to 1b according to each padded sector. Furthermore, the P_flag is set to 1b in the corresponding SRR entry. Different recording/playback apparatuses can use such information. 
     Accordingly, the types and definitions of the SRRs as defined by the present invention and a method of recording the SRRI according to the defined SRR types and definitions, are provided. Accordingly, various recording/playback apparatuses having desired functions can be used to access the present disc. 
     In addition, the second method for recording and playing back data by recovering the optical disc will be described. When an optical disc is loaded into the recording/playback apparatus, the microcomputer  16  controls the pickup unit  11  to read the latest SRRI recorded in the set management area such as TDMA of the corresponding disc. The microcomputer  16  determines whether the latest SRRI is damaged. If it is determined that the latest SRRI is damaged, the latest SRRI is estimated and recovered from non-damaged SRRIs as described above referring to  FIGS. 12 ,  13 A and  13 B. When the opened SRR is changed into the closed SRR by a close command, the dummy data with which the disc is padded is checked, so that the latest SRRI can be recovered as described above. 
     If the recovered latest SRRI or the original latest SRRI is not damaged, the recording/playback unit  10  checks the location of the additionally recordable opened SRR based on the corresponding latest SRRI, records data, receives a close command of the controller  20 , pads some portion (or entire area) of an additionally recordable area remaining in the opened SRR with dummy data, and represents that the SRR is changed to a closed SRR. The changed disc recording status is recorded as a new (latest) SRRI in a management area. After that, when the corresponding optical disc is loaded again, the final disc recording status can be exactly checked from the latest SRRI. 
     The method for recording management information of the write-once optical disc according to the present invention includes defining new SRR types and session types. If an open SRR is padded or if the SRR is closed by padding, padding identification information Padding_flag is set appropriately and recorded in the padded area. Other padding identification information P_flag is recorded in the SRR entry. Consequently, in the write-once optical disc having the new physical structure, the management information can be effectively recorded and managed. When the SRR is closed after padding, the padding information can be used to recover the damaged SRRI. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.