Abstract:
A method for defect management of an optical disc. The optical disc includes a plurality of data blocks and a plurality of spare blocks, each data block is for recording data, each spare block is for replacing a defect data block to record a data. The method includes recording a status of the spare blocks in a status table according to a location order of the spare blocks, such that the statuses of neighboring spare blocks with different statuses are recording in neighboring items of the status table.

Description:
BACKGROUND OF INVENTION 
   1. Field of Invention 
   A method for managing the spare blocks of an optical disc, more particularly one based on using the spare block address to access the spare block usage status. 
   2. Description of the Prior Art 
   Because an optical disc is inexpensive, compact, light in weight, and can store a huge amount of data, optical discs are becoming the most frequently used data storage media in the modern information society. With the introduction of a writable optical disc allowing each user to write his or her own data onto the optical disc to meet personal needs, the optical disc is becoming one of the most important portable personal storage media. How to access data on the writable optical disc more reliably and more efficiently is now a focal point of research in the modern information industry. 
   An optical disc drive is necessary to access data on the optical disc. Please refer to  FIG. 1 .  FIG. 1  is a functional block diagram of a typical optical disc drive  10  that is used to access an optical disc  22 . There is a loader  14  to hold the optical disc  22  in the optical disc drive  10 , one motor  12  that spins the loader  14 , a control circuit  18  that controls operation of the optical disc drive  10 , and a memory  20  (such as a volatile random access memory) to temporarily hold the data needed by the controlling circuit  18  during an operational period. The optical disc  22  has tracks  24  to record data. After the optical disc  22  is put on the loader  14 , the motor  12  will drive the loader  14  and the tracks  24  on the optical disc  22  will rotate across a pick-up head  16 . Using the pick-up head  16 , the control circuit  18  can access the data on the tracks  24 . The control circuit  18  is controlled by a host  26  to access data on the optical disc  22 . The host  26  can be a computer system such as PC. 
   To make the recording of data onto the optical disc  22  more reliable, there is a certain defect management mechanism in more advanced optical disc specifications. One of the most common ways is to allocate a portion of the optical disc  22  as a spare recording area. Whenever there are defects on an optical disc that make recording impossible, the data that is supposed to be recorded in the defective area will then be recorded in the spare recording area instead. Thus, the defects will not affect the recording of data on the optical disc  22 . 
   Please refer to  FIG. 2 .  FIG. 2  shows the allocation of spare recording areas and normal recording areas under the specification of CD-MRW(Compact Disc-Mount Rainier reWritable). As shown in  FIG. 2 , the track  24  that is used for data recording is divided into several major areas. These areas include a Lead-In Area (LI), a Program Area (PA), and a Lead-Out Area (LO). The LI and the LO are used respectively for marking the beginning and the end of the tracks  24 . The LI comprises one area as a Main Table Area (MTA) to store a Defect Table (DT). The PA is used to record data. The PA is divided into a pre-gap (P 0 ), a General Application Area (GAA), a Secondary Table Area (STA) to store a backup copy of the defect table DT, a plurality of Data Areas (DA), and a plurality of Spare Areas (SA). 
   In  FIG. 2 , different Data Areas (DA) are marked as DA( 1 ), DA( 2 ), . . . all the way to DA (N). There is also a plurality of Spare Areas (SA) in the PA to match the DA, different SA are marked with SA( 1 ), SA( 2 ), . . . to SA(N) respectively. Every DA has a plurality of Data Packet Areas (Pd). Every Pd has a plurality of user data blocks (Bd). Every Bd is used to record one block of data. Similarly, every SA(n) is further divided into a plurality of Spare Packet Areas (Ps). Every Ps comprises a plurality of spare data blocks (Bs). To facilitate discussion later on, there are three data blocks specifically marked Bd 1 , Bd 2 , and Bd 3  and another three spare blocks specifically marked Bs 1 , Bs 2 , and Bs 3  shown in  FIG. 2 . Whether it is the data block Bd or spare the block Bs, they are all writable data blocks with the same data storage capacity. For instance, in the specification of CD-MRW, every data area DA generally has 136 Pd and every packet Pd has 32 user data blocks Bd, every spare area SA has 8 packets Ps and every packet Ps has 32 spare blocks Bs. Every user data block Bd and spare area Bs contains room for 2 k bytes of data respectively. 
   In order to manage these data blocks Bd and spare blocks Bs, every data block Bd and spare block Bs has its own address (i.e. PBN, Physical Block Number). On the track  24 , the address of each data block Bd and spare block Bs is unique. The value of each address corresponds to the physical order of the Bd, Bs on the track  24 . An arrow A 1  in the  FIG. 2  points from the left to the right, the data area Bd on the left hand side has smaller address value. For example, in  FIG. 2 , the address value of the data area Bd is smaller than the address value of the data area Bd 2  and the address value of data area Bd 2  is smaller than that of Bd 3 , etc. The address value of every data block Bd in the data area DA( 1 ) is smaller than the address value of a data block Bd in the data area DA( 2 ), etc. Similarly, the address value of a spare block Bs 1  is smaller than that of Bs 2  and the address value of spare block Bs 2  is smaller than that of Bs 3 . The address value of every spare block Bs in the spare area SA( 1 ) is smaller than the address value of every spare block in the spare area SA( 2 ). 
   We can describe the basic principle of the optical disc  22  defect management as follows. Whenever the optical disc drive  10  needs to write data from the host  26  (refer to  FIG. 1 ) to the optical disc  22 , the optical disc drive  10  will first write data onto a data block Bd(i) of the track  24 . If the optical disc drive  10  encounters a defect and can not record data to the data block Bd(i) correctly, the optical disc drive  10  will find a substitute spare block Bs and write the data that was meant to be in this defective data block Bd(i)into the substitute spare block Bs. 
   In practice, the address of every defective data block Bd, the address of the substituted spare block Bs, and a mapping indicating the relationship is recorded in the defect table DT of the optical disc  22 . When the optical disc drive  10  wants to read from the optical disc  22  and reaches the defective data block Bd, it locates the corresponding substituted spare block Bs via a record in the defect table DT, and reads the data on this substituted spare block Bs. According to the operational principle described above, even with some defects on the optical disc  22 (caused by scratches or microdust), by setting up and using spare blocks Bs to implement defect management via the defect table DT, data can still be recorded on the optical disc  22 . 
   As described above, the defect table DT records the usage status of each spare block Bs. Please refer to  FIG. 3 .  FIG. 3  is a sketch map of the main data structure of the defect table DT in  FIG. 2 . The defect table DT has a plurality of Defect Table Blocks (DTB) (different Defect Table Blocks are marked DTB( 1 ), DTB( 2 ) . . . respectively). Each DTB has a plurality of entries  28 . A plurality of DTB can be collected to form one defect table packet, so the DTB in the defect table DT can be divided into a plurality of defect table packets. 
   The total number of DTB in the defect table DT is the same as the number of spare areas SA in the track  24 . The number of entries  28  in each DTB is the same as the number of the allocated spare blocks Bs in the spare area SA. In other words, every entry  28  in the defect table DT maps to one spare block Bs and records the usage status of this spare block Bs. Basically, each DTB maps to one spare area SA and every entry  28  of DTB is used to record the usage status of one spare block Bs in the corresponding spare area SA. However, in some special cases, there will be some entries  28  in the DTB that record a spare block Bs usage status of another spare area SA. 
   Please refer to  FIG. 4A .  FIG. 4A  is a detailed sketch map of the data structure of the defect table DT. As shown in  FIG. 4A , the spare area SA(n−1) on the track  24  contains spare block SO. The spare area SA(n) has spare blocks S 1  through S 16 . The data area DA(n−1) includes data blocks Dx through Dy. The data area DA(n) includes data blocks D 1  through D 7 . In the defect table DT, the data block DTB(n−1) is mainly used to record the usage status of corresponding spare blocks in the spare area SA(n−1). In every entry  28  that maps to one spare block Bs records one status information  29 A, one spare block Bs address information  29 B, and one data block Bd address information  29 C. The spare block Bs address information  29 B records the spare block Bs address mapped to this entry. To facilitate further discussion, three entries are marked  28 A,  28 B, and  28 C respectively in  FIG. 4A . 
   For each spare block Bs on the track  24 , there are three different possibilities. First, a spare block Bs is already used to substitute for a defective data block Bd and contains the data that was supposed to be written onto this defective data block Bd. Second, although the spare block Bs can record data normally, it is not yet used to substitute for a defective data block Bd. Third, the spare block is defective and cannot be used to record any data. 
   For example, in  FIG. 4A , the spare block S 0  of the spare packet SA(n−1) and the spare blocks S 1 , S 2 ,S 3 ,S 5 ,S 6 ,S 8 ,S 10 , and S 11  of the spare packet SA(n) are used as substitutes to record data originally meant for specific defective data blocks Bd. The entries  28  that were used to record the usage status of these spare blocks Bs can also be called “used entries”. The spare blocks Bs that these entries map to were used to substitute for the defective data blocks Bd. 
   For instance, an entry  28 A is used to record the usage status  29 A of the spare block S 5  and the address information  29 B of the spare block S 5 . If the spare block S 5  is used to substitute for a defective data block D 3  for data recording, then the data block address information  29 C of the entry  28 A will record the address of the data block D 3 . Finally, the status information  29 A is used to mark the entry  28 A as a used entry. In  FIG. 4A , a “U” is used to mark a used entry  28 . In practice, the status information  29 A is a  4  bit data. Similarly, the correspondences of the spare blocks S 2 , S 0 , S 1 , S 6 , S 5 , and S 3  that are used to substitute for defective data blocks Dx, Dy (which reside in the data area DA(n−1)), D 1 , D 2 , D 3 , and D 7  respectively, are each mapped in used entries  28 A. All of the used entries  28 A are gathered together and form a group in the record block DTB(n) as shown on  FIG. 4A . 
   When the optical disc drive  10  tries to access data in a defective data block Bd on the optical disc  22 , the optical disc drive  10  uses the address of this defective data block Bd to find the corresponding entry  28 A that records the address  29 C of this defect data block Bd. The optical disc drive  10  then uses the address  29 B of the corresponding spare block Bs via this entry to use this spare block Bs to substitute for the original defective data block Bd for data accessing. 
   The spare blocks S 13 , S 14  to S 15 , and S 16  in  FIG. 4A  are all normal recordable spare blocks Bs, but they are not yet used to substitute for a defective data block Bd. The entries  28 B recording the usage status  29 A of these spare blocks Bs are called “free entries”. For instance, the entry  28 B of the spare block S 15  is a free entry. The spare block address information  29 B of the entry  28 B will record the address of the spare block S 15 . Because the spare block Bs that maps to a free entry is not yet used to substitute for a defective data block Bd, the data block address information  29 C will not record the address of a specific data block Bd. In  FIG. 4A , the status information  29 A is marked with an “F” to indicate that the entry  28 B is a free entry. Based on the same reasoning, the status information  29 A of the spare blocks S 13 , S 14 , and S 16  are also marked with an “F” in the respective entries  28 B. Similar to the allocation of used entries, in a record block DTB(n), all of the recordable free entries are also gathered together to form a group, as shown in  FIG. 4A . 
   Just like the data blocks Bd can be damaged and become defective data blocks Bd, the spare blocks Bs in the spare area SA can also be damaged and become defective spare blocks Bs. For instance, in  FIG. 4A , spare blocks S 4 , S 7 , S 9 , and S 12  are defective spare blocks. Entries  28 C that are used to record the usage status  29 A of the spare blocks S 4 , S 7 , S 9 , and S 12  are called unusable entries. For example, the address of the defective spare block S 4  is recorded in the spare block address information  29 B of the unusable entry  28 C. The defective spare block S 4  cannot be used to substitute for any defective data block Bd for data recording, so the data block address information  29 C of the data entry  28 C will not record an address of any specific data block Bd. In  FIG. 4A , the status information  29 A is marked “D” to indicate that the entry  28 C is an unusable entry. Similarly, the defective spare blocks S 7 , S 9 , and S 12  are also recorded as unusable entries. For the same record block DTB, all of the unusable entries  28 C are also gathered together to form a group as shown in  FIG. 4A . 
   From the description above, the usage status  29 A of any spare block Bs is known based on the possible three entries (used, free, and unusable). In order to streamline the process of defect management, the entries of the record block DTB in the defect table DT are sorted. As described above, the data blocks Bd and the spare blocks Bs all have addresses. Every used entry  28  in the defect table is sorted into ascending order by the address of the defective block  29 C. 
   Take  FIG. 4A  as an example, the defective data blocks Bd from left to right are Dx, Dy, D 1 , D 2 , and D 3  to D 7 . The data block Dx has the lowest address value, and from left to right the value increases (Dx&lt;Dy&lt;D 1 &lt;D 2 &lt; . . . &lt;D 7 )with the data block D 7  having the highest address value. The used entries  28 A that record the addresses of these defective data blocks are also sorted by the address value order of defective data blocks Bd. As shown in  FIG. 4A , in a data block DTB(n), among all the used entries  28 A, the used entry  28 A that records the address of the data block Dy is arranged at the left hand side of the diagram, and the order of the used entries  28 A is according to the order of the addresses of the data blocks Dy, D 1 , D 2 , and D 3  to D 7 . In practice, all the used entries  28 A in the record block DTB of the defect table DT will follow the magnitude order of the defective data block address. In other words, in the record block DTB(n−1), of all the defective data block addresses recorded by the used entries  28 A, the highest address is the rightmost address. In the record block DTB(n), every defective data block address recorded by the used entries  28 A will be higher than the rightmost address in the record block DTB(n−1). 
   Compared to the order arrangement of the used entries  28 A in the defect table DT, the order the free entries  28 B is based on the spare block Bs addresses that the free entries  28 B record. In  FIG. 4A , the spare blocks Bs from left to right are S 1 , S 2 , S 3  through S 14 , S 15 , and S 16 . The spare block S 1  has the lowest address value, and from left to right the value of each address increases (S 1 &lt;S 2 &lt;S 3 &lt; . . . &lt;S 14 &lt;S 15 &lt;S 16 ) with the spare block S 16  having the highest address value. For the spare blocks S 13 , S 14 , S 15 , and S 16  that are not used to substitute for defective data blocks Bd, the corresponding free entries  28 B also follow the same order from left to right as shown in  FIG. 4A . Unusable entries  28   c  do not require any special sorting. 
   When the optical disc drive  10  accesses the data block Bd in the data area DA(n) sequentially, the optical disc drive  10  encounters the defective data blocks D 1 , D 2  and D 3 . If the data area DA(n)is arranged according to the address of the defective data block Bd sequence and used entries  28 A are sorted as a group, the optical disc drive can retrieve the address of the substituted spare block Bs via the used entry  28 A. Based on the address sequence to arrange the spare blocks Bs and the gathering of the free entries  28 A, the optical disc drive  10  can find free spare blocks  28 B to substitute for the defective data blocks Bd. 
   However, because these three types of entries (used, free, and defective) are gathered to form groups and sorted differently according to their types, the number and position of all the entries  28  in the defect table DT will change with repeated data accessing. Please refer to  FIG. 4B  (and also  FIG. 4A ).  FIG. 4B  shows, if the optical disc  22  status changes, how the defect table from  FIG. 4A  is affected. Suppose during the operation of data writing, the optical disc drive  10  finds a normal data block B 8  on track  24  has become defective (in other words, the data block B 8  is normal in  FIG. 4A  but is defect in  FIG. 4B ). The optical disc drive  10  can no longer write data to the data block B 8 . Following the defect management principles mentioned earlier, the optical disc drive  10  searches for a free entry  28 B in the defect table DT to find a free spare block  28 A (not used as a substituted block for any defective data block)and locates the spare block S 13 . Then the spare block S 13  is used to substitute for the defect data block D 8 . 
   After the usage status  29 A of the free entry  28 B for the spare block S 13  is changed from “free” to “used”, the free entry  28 B that records the address of the spare block S 13  in the record block DTB(n) will be a used entry. The changed status information  29 A from an “F” to a “U” makes the free entry  28 B become a “New” used entry  28 A. Of course, now there is one less free entry in  FIG. 4B  than in  FIG. 4A . 
   As described above, the used entries  28 A need to be sorted. Because the address value of the data block B 8  is somewhere between the defective data blocks D 1  and D 2  the “New” used entry  28 A has to be put in between the two used entries  28 A that record the defective blocks D 1  and D 2 . From this example it can be seen that the order of the used entries  28 A after sorting may be different from the corresponding spare block Bs sequence arranged on the track  24 . 
   Furthermore, as shown by  FIGS. 4A and 4B , if there are more defective data blocks Bd in the data area DA(n−1) than the normal spare blocks Bs in the spare area SA(n−1), the spare blocks Bs in the spare area SA(n) are used. When the used entries  28 A are sorted according to the defective data block Bd addresses, the used entry  28 A that records the spare block S 2  originally in the spare are SA(n) might be placed in the record block DTB(n−1) that normally maps to the spare area SA(n−1). Similarly, for the spare block S 0  that belongs to the spare area SA(n−1), the used entry  28 A might be moved to the record block DTB(n). In response to the “New” used entry  28 A, the defect table DT with changed content will be rewritten onto the optical disc  22 . Afterwards, when the optical disc  10  is accessing data and encounters the defective data block B 8 , from the updated defect table DT it can locate the corresponding spare block S 13 . 
   From the discussion above, after repeated data accessing, the optical disc  22  will eventually have defects. The entry number and sequence of the defect table DT will keep changing too. Because the used entries  28 A and the free entries  28 B are grouped and sorted within their respective groups, the entries  28  used to record the usage status  29 A of the spare blocks Bs can no longer be arranged sequentially according to the spare blocks Bs sequence on the track  24 . For instance, as mentioned in  FIGS. 4A ,  4 B, even with the spare blocks S 12 , S 13 , and S 14  on neighboring positions on track  24 , the entries  28  used to record the usage status  29 A of the spare blocks S 12 , S 13 , and S 14  will not lineup in neighboring positions and follow the sequence of the spare blocks S 12 , S 13  and S 14 . 
   Even within the used entries  28 A of every record block DTB, the spare blocks Bs with neighboring entry  28  records are not necessary the neighboring spare blocks Bs on the track  24 . In other words, the defect table DT based on the spare block usage status  29 A cannot reflect the actual sequence of the spare blocks Bs on the track  24 . 
   If the address of the spare block Bs is needed to refer to the usage status  29 A of this spare block Bs, the spare block Bs address information  29 B of each spare block Bs in the defect table DT must be checked one by one to retrieve the status of this spare block Bs via the status information  29 A from the entry  28 . For instance, if the optical disc drive  10  encounters one defective spare block Bs in some spare area SA during optical disc  22  data accessing, the spare block Bs address information  29 B of all the unusable entries  28 C is checked one by one to find out if this spare block Bs is already recorded in the defect table DT as a defective spare block Bs. If this spare block Bs is not recorded as a defective spare block Bs yet, this spare block Bs might be recorded as a spare block Bs in a free entry  28 B. Now the usage status  29 A of the entry  28 B must be changed accordingly. Because there is no way to directly retrieve the usage status  29 A of the spare block Bs simply by address, the process of defect management is cumbersome and slow. 
   SUMMARY OF INVENTION 
   The primary objective of the claimed invention is to disclose a method that can manage the usage status of spare blocks efficiently, and to directly control the usage status of spare blocks according to the address of the spare block. 
   The claimed invention sets up a status table in addition to a defect table. The status table has a plurality of fields with each field mapping to one spare block on the optical disc and is used to record the usage status of that particular spare block. All fields in the status table are arranged in the same order as the spare blocks they map to on the optical disc. After the construction of the status table according to the claimed invention, the defect distribution density and related statistic data in different data areas and spare areas is easily available, further assisting data accessing on the optical disc. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a functional block diagram of a prior art optical disc drive. 
       FIG. 2  is a sketch map of the data format on an optical disc track. 
       FIG. 3  is a sketch map of the main data structures of a defect table of the optical disc track in  FIG. 2 . 
       FIG. 4A  is a sketch map of the detailed data structure of the defect table in  FIG. 3 . 
       FIG. 4B  shows how the defect table in  FIG. 4   a  is updated as the status of the optical disc changes. 
       FIG. 5  is a functional block diagram of an optical disc drive according to the present invention. 
       FIG. 6  is a sketch map of main data structure in a status table according to the present invention. 
       FIG. 7A  is a sketch map of the main data structures in the status table of  FIG. 6 . 
       FIG. 7B  shows how a defect table is updated as the status of an optical disc changes according to the present invention. 
   

   DETAILED DESCRIPTION 
   Please refer to  FIG. 5 .  FIG. 5  is a functional block diagram of a present invention optical disc drive  30  with a host  46 . The method of the present invention can be used with the optical disc drive  30  of  FIG. 5 . With the host  46  (can be a computer system such as a PC), users can control the optical disc drive  30  to access data on an optical disc  22 . There is a loader  34  in the optical disc drive  30 , one motor  32  that spins the loader  34 , a control circuit  38  that controls the operation of the optical disc drive  30 , and a memory  40  (for instance, random access memory) to temporarily hold the data needed for the control circuit  38  during an operational period. When the motor  32  drives the loader  34 , the optical disc  22  on the loader  34  rotates and tracks  24  on the optical disc  22  that are used for recording data will sweep across a pick-up head  36 . The pick-up head  36  then accesses the data on the tracks  24 . The data protocol recorded on the track  24  can be of the CD-MRW specification shown in  FIG. 2 . 
   To control the usage status of all the spare blocks more efficiently, in addition to an original defect table on the optical disc  22 , the present invention adds a status table to record the usage status of all spare blocks according to their sequence order on the track  24 . The status table is kept in the memory  40  for use by the control circuit  38  and is not necessarily written to the optical disc  22  to retain compatibility with the CD-MRW protocol. 
   Please refer to  FIG. 6 .  FIG. 6  is a sketch map that shows the data structure of the status table  50  of the present invention mapping with the spare blocks Bs on the optical disc track  24 . In the status table  50  of the present invention, there are a plurality of fields  52  (for easier discussion in the future, nine fields are marked  52 A to  52 I), every field maps to a spare block Bs on the track  24  and records the usage status of that spare block Bs. Most importantly, in the present invention, the fields  52  that map to the spare blocks Bs correspond to the order of the spare blocks Bs on the track  24  and lineup accordingly in the status table  50 . As shown in  FIG. 6 , from left to right in the diagram, fields  52 A,  52 B, and  52 C in the status table  50  map to spare blocks Sa 1 , Sa 2 , and Sa 3  in spare area SA( 1 ) using the same order. The fields  52 A and  52 B map to the neighboring spare blocks Sa 1  and Sa 2 , so they are also in neighboring positions in the status table  50 . Fields  52 D,  52 E, and  52 F map to spare blocks Sb 1 , Sb 2 , and Sb 3  in spare area SA( 2 ) respectively and lineup in the status table  50  in the same order as the spare blocks Sb 1 , Sb 2 , and Sb 3 . The field  52 C that maps to the last spare block Sa 3  in the spare area SA( 1 )(the one at the left) will also neighbor the field  52 D that maps to the first spare block Sb 1  of the spare area SA( 2 ). 
   The same rule applies to the last spare area SA(N) of track  24 , fields  52 G,  52 H, and  52 I map to data blocks Sz 1 , Sz 2 , and Sz 3  and lineup at the last part of the status table  50 . Compared to the first field  52 A in the status table  50  (maps to the first spare block Sa 1  in the first spare area SA( 1 )), the last field  521  in the status table  50  maps to the last spare block Sz 3  on the track  24 . 
   For further notes on the implementation of the present invention, please refer to  FIG. 7A . For easier comparison of the data structures between the status table  50  of the present invention and the defect table DT,  FIG. 7A  is a sketch map to show how the status table  50  of the present invention is used to record the usage status of the spare blocks Bs in  FIG. 4A . In a preferred embodiment of the present invention, the field  52  that maps to one spare block Bs will record whether this spare block Bs is free, is used to substitute for a defective data block Bd, or if the spare block Bs is defective. 
   For instance, the spare block S 1  is used to substitute for one defective data block Bd. A field  54 A that maps to the spare block S 1  records that the spare block S 1  is a used spare block Bs. Similarly to the example in  FIG. 4A ,  FIG. 7A  also uses a “U” in the field to show that the spare block S 1  is already used to substitute for a defective data block Bd. Similarly, a field  54 B to the right of the field  54 A maps to a spare block S 2  and records that the spare block S 2  is already used to replace a defective data block Bd. 
   On the other hand, a field  54 D in the status table  50  that maps to a defective spare block S 4  records that the spare block S 4  is a defective spare block Bs and cannot record data. The fields  54  in  FIG. 7A  use a “D” to represent a defective spare block Bs. Similarly, a field  54 G that maps to a spare block S 7  is also marked with “D”, indicating that it is also a defective spare block Bs. 
   Finally, in  FIG. 7A , all the fields  54  that map to a free spare block Bs (spare blocks Bs that are not defective and are not used to substitute any defective data block Bs yet) will have an “F” in the field representing that the spare block Bs that the field  54  maps to is a free spare block Bs. For instance, fields  54 M,  54 N, and  54 P in the status table  50  record that the spare blocks S 13 , S 14 , and S 16  are all free spare blocks Bs. 
   Please refer to  FIG. 7B  (and also  FIG. 7A ). As with the discussion of  FIG. 4A  and  FIG. 4B  above, during the process of data accessing on the optical disc  22 , the usage status of every spare block Bs might change. The status table  50  of the present invention will be able to update the status change of every spare block Bs. For example, in the transformation of  FIG. 4A  into  FIG. 4B , a data block B 8  in  FIG. 7A  used to be functional, but during the process of data accessing on the optical disc  22 , the data block B 8  became a defective data block and cannot record data anymore. When the optical disc drive  30  tries to write data into the data block B 8 , the optical disc drive  30  discovers that the data block B 8  is defective and will look for a substitute spare block Bs. If the optical disc drive  30  decides to substitute spare block S 13  for the data block B 8 , the usage status of the spare block S 13  will change from “free” to “used”.  FIG. 7B  shows a sketch map for the status table  50  mapping update. 
   Because the spare block S 13  maps to a field  54 M in the status table  50 , the field  54 M was previously marked with an “F” in  FIG. 7A  (to indicate that the spare block S 13  is free). After the spare block S 13  in  FIG. 7B  is used to substitute for the data block B 8 , the field  54 M in the status table  50  is changed into a “U”, indicating that the spare block S 13  that the field  54 M maps to is now used to substitute for a defective data block Bd. 
   Even with the change of usage status of the spare block S 13 , the spare block S 13  still maps to the field  54 M in the status table  50 . Regardless if in  FIG. 7A  or  FIG. 7B , the neighbors of the field  54 M are still fields  54 L and  54 N, they still map to the spare blocks S 12  and S 14  which are neighbors of the spare block S 13 . In other words, even with usage status changes of every spare block Bs, the order of their corresponding fields in the status table  50  is still the same as the order of the spare blocks Bs on the track  24 . 
   In practice, in the preferred embodiments of the status table  50  of the present invention, every field  54  can be a one byte (8 bits) data, 2 bits can be used to record the usage status of the spare block Bs (total 3 status, “U”, “D” and “F” in  FIG. 7A ) and the remaining 6 bits can be reserved for other related data. For instance, the address of the substituted defective data block Bs can be recorded in the mapping field  54  of the used spare block Bs. In other words, in the field  54  that maps to a spare block Bs, in addition to recording the usage status of that spare block Bs as used, free, or unusable (defective), the field  54  can also record other related data of that spare block Bs. Under the circumstance that every field  54  is one byte of data, if there are M spare blocks Bs on the track  24 , the status table  50  of the present invention will be M bytes of data. 
   When the optical disc drive  30  (refer to  FIG. 5 ) starts to access data on the optical disc  22 , the control circuit  38  of the optical disc drive  30  will first read the defect table DT of the optical disc  22  into the memory  40 . In the mean time, the control circuit  38  will construct the status table  50  of the present invention based on the defect table DT in the memory  40 . For instance, M bytes of the memory  40  is allocated to store the status table  50 , then every field  54  in the status table  50  is filled out based on the content of every entry  28  in the defect table DT. 
   In practice, the control circuit  38  can execute a simple program (or use a simple logic circuit) to calculate which byte (field  54 ) of the status table  50  a spare block Bs is mapped to according to the address of the spare block Bs, allowing access to the information in the field  54  in the status table  50 . When the optical disc drive  30  starts to access data on the optical disc  22 , from the status table  50  the optical disc drive  30  can find the mapping field  54  according to the spare block Bs address, and can access the data within this field  54 . For instance, when the optical disc drive  30  encounters a defective spare block Bs on the optical disc  22  during data accessing, the control circuit  38  determines whether this defective spare block Bs is marked “unusable” in the status table  50  by the address of this defective spare block Bs. In comparison to the prior art, the optical disc drive  10  has to check every unusable entry in defect table one by one to know whether that defective spare block Bs is marked as defective (unusable) already. 
   As the examples shown in  FIGS. 7A ,  7 B (and  FIGS. 4A ,  4 B) demonstrate, in response to events occurring during a data accessing period of the optical disc  22 , the optical disc drive  30  has to update the content of defect table DT and the status table  50  accordingly. Normally, after the optical disc drive  30  reads the defect table DT and stores it temporarily in the memory  40 , whenever the defect table DT needs to be updated, the optical disc drive  30  will only update the defect table DT in the memory  40 . Updating the status table  50  is also a fast memory operation. 
   After the optical disc drive  30  finishes accessing data on the optical disc  22  (for instance, the optical disc  22  is to be ejected from the optical disc drive  30 ), the optical disc drive  30  will then write back the updated defect table DT in the memory  40  to the optical disc  22  (writes to the main table area MTA/secondary table area STA, as shown in  FIG. 2 ). Of course, in one embodiment of the present invention, the status table  50  of the present invention can also be written into one fixed location on the optical disc track  24 . That is, if the status table  50  of the present invention has been recorded onto the optical disc  22  in a prior session, before the optical disc drive  30  starts to access the optical disc  22 , the optical disc drive  30  can load the status table  50  from the optical disc  22  into the memory  40  and update the temporary status table  50  in the memory  40  during as needed. If the status table  50  is changed during a session, before finishing the optical disc  22  data accessing, the updated status table  50  will be written back onto the optical disc  22 . 
   With the prior art, only the defect table DT is used to record the usage status  29 A of every spare block Bs. Because the defect table DT categorizes every spare block Bs by its individual usage status  29 A, it is impossible to quickly determine the usage status  29 A of the spare block Bs simply by using the address of the spare block Bs. 
   The status table  50  of the present invention acts as an accessory tool for the defect table DT and records the usage status  29 A of every spare block Bs in the order of the spare blocks Bs on the optical disc track  24 . The usage status  29 A of the spare block Bs can be retrieved according to the address of the spare block Bs, resulting in a more efficient defect management mechanism. 
   Additionally, from the status table  50  of the present invention, calculating the number of defective blocks and related statistic data of the optical disc  22  is quick and it can be used as the basis for optical disc  22  data accessing. For instance, the number of defective data blocks on the optical disc  22  (based on the number of used spare block) can quickly be calculated from the status table  50  before the optical disc drive  30  accesses data. For an optical disc  22  with fewer defective data blocks Bd, the default spin speed of the optical disc drive  30  can be faster allowing the optical disc drive  30  to access data on the optical disc  22  at a higher speed. Contrarily, if the optical disc  22  has more defective data blocks Bs, the optical disc drive  30  will perform more frequent defect management functions (such as moving the pick-up head to a spare area SA and accessing the data on the spare blocks Bs). In this case, the default speed of optical disc drive  30  can be lower, so that the optical disc drive  30  can perform more frequent defect management processing at a slower speed. 
   Furthermore, from the status table  50  of the present invention, the distribution status of the used spare block Bs can be calculated. If most of the spare blocks Bs in some spare area SA are used spare blocks Bs, the optical disc drive  30  can also read these spare blocks into the memory  40 . Because later on during the data accessing process of the optical disc  22 , the optical disc  22  is very likely to access these spare blocks Bs to perform a defect management function. If these spare data blocks Bs are read into the memory  40  beforehand, the pick-up head needs not move on the track  24  to access these spare blocks Bs. In conclusion, by using the status table  50  of the present invention, the inadequateness of the defect table is overcome and the processes of optical disc data accessing and defect management are more efficient. 
   Described above is only the preferred embodiments of the present invention. Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.