Abstract:
A data updating apparatus updates a plurality of pieces of data that constitutes a file in a storage medium. The storage medium stores (a) first and second FATs which indicate data storage locations and data sequences and (b) file indexes which each correspond to a file and associate a file name with a storage location of a top piece of data of a file. In the data updating apparatus, an updating unit updates the first FAT, the corresponding file index, and the second FAT in the stated order in updating of the file; a temporary index generating unit generates a temporary index including a storage location of the corresponding file index and new contents of the corresponding file index, and writes it into the storage medium before the first FAT updating; and a temporary index deleting unit deletes the temporary index from the storage medium after the second FAT updating.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a data updating apparatus that writes data into a storage medium such as a semiconductor memory, a magnetic disc, and an optical magnetic disc, and especially relates to a technique of restoring consistency after abnormality in data writing causes inconsistency between file management information and the actual storage state of data which constitutes a file. 
     (2) Prior Art 
     Information equipment such as a personal computer writes data into a storage medium such as a hard disc, based on a file system. In a file system to write data not into contiguous memory locations in a storage medium but divide the data into pieces (hereinafter called “divided pieces of data”) and write them into clusters, a FAT (File Allocation Table) and a file index are used. Here, the FAT shows information such as locations of the clusters storing the divided pieces of data and the sequence in which they form a file (hereinafter called “data sequence”). The file index associates a name of the file and a storage location where the top divided piece of data is stored. 
     The information equipment reads/writes the data from the top divided piece of data to the last divided piece of data in accordance with the FAT and the file index by sequentially tracing the clusters storing the divided pieces of data. 
     Conventionally, a data updating apparatus is used to update data in the information equipment which employs the file system including the FAT. 
     FIG. 1 is a functional block diagram showing a conventional data updating apparatus  1000 . 
     The data updating apparatus  1000  is roughly made up of a storage medium  1001 , a CPU (Central Processing Unit)  1002 , and a RAM (Random Access Memory)  1003 , each of which is connected by a bus. The CPU  1002  controls reading/writing of data from/into the storage medium  1001 , and the RAM  1003  temporarily stores the data written or read by the CPU  1002 . 
     The storage medium  1001  stores a first FAT  1005 , a second FAT  1006  which are obtained by duplexing a FAT, file indexes  1007 ,  1008 ,  1009 , . . . , and divided pieces of data  1010 ,  1011 ,  1012 , . . . . 
     FIG. 2 shows the relationship between the first FAT  1005 , the second FAT  1006 , the file indexes  1007 ,  1008 ,  1009 , . . . , and a data storage area  1260 . 
     First, the file indexes  1007 ,  1008 ,  1009 , . . . , are explained. 
     File indexes  1007 ,  1008 ,  1009 , . . . , are tables which are each generated for a file. Since their data structures are the same, the file index  1007  is explained here as an example. 
     A file name field  1211  shows a filename “File1.doc”,; an entry cluster number field  1222  shows a number “ 2101 ” of a cluster storing the top divided piece of data of the file; a data size field  1223  shows a total data size “93” of the file in kilo bytes; an attribute field  1224  shows an attribute “writable” of the file; and a time stamp field  1225  shows “00/11/02/11:28”, which is a date and a time when the file index  1007  was generated or updated. 
     Next, the first FAT  1005  and the second FAT  1006  are explained. 
     Although usually one FAT is sufficient, the FAT is duplexed to be the first FAT  1005  and the second FAT  1006  for backup in case of abnormality during FAT updating. Since the contents of the first FAT  1005  and the second FAT  1006  are the same, the first FAT  1005  is explained here as an example. 
     The first FAT  1005  is used for tracing the clusters which store the divided pieces of data in the data sequence. 
     Each cluster is composed of several sectors, which are the smallest storage units on the storage medium  1001 . 
     A cluster number column  1241  shows a number which specifies a cluster, namely a cluster number. 
     A pointer column  1242  shows a cluster number of a cluster storing a divided piece of data immediately following a divided piece of data stored in the cluster shown by the cluster number column  1241 . 
     Here, if there is no following divided piece of data, the pointer column  1242  shows an End code which indicates that the following divided piece of data does not exist. 
     Next, the storage state of the divided pieces of data in the clusters is explained. 
     A data storage area  1260  is a group of clusters. Each cluster stores one of the divided pieces of data, based on the locations of the clusters and the data sequence indicated by the first FAT  1005  and the second FAT  1006 . 
     That is to say, to obtain data of the file name “File1. doc”, the CPU  1002  searches the file indexes  1007 ,  1008 ,  1009 , . . . for the file name “File1.doc”, obtains the file index  1007  which shows the file name “File1.doc”, and obtains the entry cluster number “2101”. 
     Next, the CPU  1002  obtains a pointer “2106” with reference to the entry cluster number “2101” in the first FAT  1005 , then obtains a pointer “2108” with reference to the cluster number “2106”, and finally obtains the End code with reference to the cluster number “2108”. 
     As a result, the CPU  1002  finds out that the data of the file name “File1.doc” is made up of the divided pieces of data  1010 ,  1011 , and  1012  that are stored in the clusters with the cluster numbers “2101”, “2106”, and “2108” in sequence. The CPU  1002  then reads the divided pieces of data from the clusters and assembles them, to obtain the data of the file. 
     When performing file updating by appending or changing data, the CPU  1002  first stores new divided pieces of data necessary for the updating into available clusters, then changes the contents of a corresponding file index such as a data size, updates the cluster numbers and the pointers in the FATs, and deletes divided pieces of data which become unnecessary from clusters. 
     Here, when updating a file only slightly, not all the divided pieces of data that form the file are subjected to the updating, but only part of them is subjected to the updating in units of clusters. 
     During such updating, if the updating of one of the FATs is interrupted due to a power failure or the like, the pointer rewriting in the first FAT  1005  or the second FAT  1006  will result in incompletion. This incompletion causes inconsistency with both states of pointers of before and after updating. Even if all of the divided pieces of data are stored in the clusters properly, the CPU  1002  cannot properly recognize their storage locations and sequence, and therefore cannot read the file properly. 
     To prevent this inconvenience, the CPU  1002  restores to a consistent state in rebooting of the data updating apparatus  1000 . 
     That is to say, when the updating of the first FAT  1005  or the second FAT  1006  is interrupted, the CPU  1002  checks the inconsistency between the first FAT  1005 , the second FAT  1006 , the file indexes  1007 ,  1008 ,  1009 , . . . , and the clusters. One of the first FAT  1005  and the second FAT  1006 , which has consistency, is used as a proper FAT, and the other is changed so as to be the same as the proper FAT. This processing restores to a consistent state. 
     As for the file indexes, since the data size of each index is small enough to store in one sector, it is not assumed here that the updating of any of the file indexes  1007 ,  1008 ,  1009 , . . . , is interrupted. 
     In recent years, a variety of digital information household electrical appliances such as digital televisions and game machines, which receive information such as video, audio, and data and write it into a storage medium such as a hard disc. 
     These digital information household electrical appliances are equipped with data updating apparatuses similar to those in personal computers. 
     The above conventional restoration processing has the following problem. 
     The conventional restoration processing takes a long time to check the inconsistency between the first FAT  1005 , the second FAT  1006 , the file indexes  1007 ,  1008 ,  1009 , . . . , and the clusters. Accordingly, the data updating apparatus takes a long time until it resumes to read/write data. 
     Therefore, especially users of digital information household electrical appliances such as the digital televisions and the game machines that are based on real time processing are likely to be irritated. 
     SUMMARY OF THE INVENTION 
     The present invention is led in consideration of the above problem, and the first object of the present invention is to provide a data updating apparatus that can shorten the restoration processing time. 
     Also, the second object of the present invention is to provide a data updating method that can perform the above improved restoration processing. 
     Furthermore, the third object of the present invention is to provide a storage medium storing a program that shortens the restoration processing time. 
     The first object is achieved by a data updating apparatus for updating a file in a storage medium which stores: (a) one or more files including the file to be updated, each of which includes a plurality of pieces of data, (b) a first table and a second table which both indicate a storage location of each piece of data and a sequence of the plurality of pieces of data of each file, and (c) one or more pieces of index information which are in a one-to-one correspondence with the one or more files and each associate a file name with a storage location of a predetermined piece of data of a file, the data updating apparatus including: a unit for updating the first table, a piece of index information corresponding to the file to be updated, and the second table in the stated order in updating of the file; a unit for generating and writing index identifying information into the storage medium before the first table is updated, the index identifying information including (i) address information which shows a storage location of the corresponding piece of index information and (ii) new contents to which the corresponding piece of index information is to be updated; and a unit for deleting the index identifying information from the storage medium after the second table is updated. 
     With this construction, if restoration processing is to be performed when the index identifying information exists in the storage medium after the file updating results in incompletion, the need of restoration processing can be easily judged by judging whether the index identifying information exists or not. Accordingly, restoration processing can be started soon. 
     The data updating apparatus further includes: a unit for judging whether the index identifying information exists in the storage medium after the updating of the file results in incompletion; and a unit for, when the index identifying information exists, restoring consistency by (a) reading the corresponding piece of index information specified by the address information, (b) comparing contents of the corresponding piece of index information with the new contents of the corresponding piece of index information included in the index identifying information, and (c) restoring consistency by (i) changing the second table so as to have same contents as the first table when the contents of the corresponding piece of index information match the new contents of the corresponding piece of index information, and (ii) changing the first table so as to have same contents as the second table when the contents of the corresponding piece of index information are different from the new contents of the corresponding piece of index information. 
     With this construction, the need of the restoration processing can be easily judged by judging whether the index identifying information exists or not. The data updating apparatus then obtains the corresponding piece of index information, based on the address information, and changes one of the first table and the second table so as to have the same contents as the other in accordance with the result of comparing the contents of the corresponding piece of index information with the new contents of the corresponding piece of index information included in the index identifying information. Consequently, without comparing these tables with the storage state of the plurality of pieces of data, the restoration processing of the first table and the second table is performed. As a result, a restoration processing time is shortened. 
     In the data updating apparatus, the index identifying information generating/writing unit sets a predetermined bit in the storage medium to a first value when writing the index identifying information, the index identifying information deleting unit sets the predetermined bit to a second value which is different from the first value when deleting the index identifying information, and the judging unit performs the judging, based on the predetermined bit. 
     With this construction, the need of restoration processing can be easily judged only by referring to the value in the predetermined bit. 
     Also, in the data updating apparatus, the restoring unit deletes the index identifying information from the storage medium and sets the predetermined bit to the second value after completing the restoring. 
     With this construction, in the second or later restoration processing, the need of restoration processing can be easily judged only by referring to the value in the predetermined bit. 
     In the data updating apparatus, the restoring unit deletes the index identifying information from the storage medium after completing the restoring. 
     With this construction, in the second or later restoration processing, the need of restoration processing can be easily judged by judging whether the index identifying information exists or not. 
     The second object is achieved by a data updating method for updating a file in a storage medium which stores: (a) one or more files including the file to be updated, each of which includes a plurality of pieces of data, (b) a first table and a second table which both indicate a storage location of each piece of data and a sequence of the plurality of pieces of data of each file, and (c) one or more pieces of index information which are in a one-to-one correspondence with the one or more files and each associate a file name with a storage location of a predetermined piece of data of a file, the data updating method including the steps of: updating the first table, a piece of index information corresponding to the file to be updated, and the second table in the stated order in updating of the file; generating and writing index identifying information into the storage medium before the first table is updated, the index identifying information including (i) address information which shows a storage location of the corresponding piece of index information and (ii) new contents to which the corresponding piece of index information is to be updated; and deleting the index identifying information from the storage medium after the second table is updated. 
     With this construction, if restoration processing is to be performed when the index identifying information exists in the storage medium after the file updating results in incompletion, the need of restoration processing can be easily judged by judging whether the index identifying information exists or not. Accordingly, restoration processing can be started soon. 
     The data updating method further includes the steps of: judging whether the index identifying information exists in the storage medium after the updating of the file results in incompletion; and restoring consistency by, when the index identifying information exists, (a) reading the corresponding piece of index information specified by the address information, (b) comparing contents of the corresponding piece of index information with the new contents of the corresponding piece of index information included in the index identifying information, and (c) restoring consistency by (i) changing the second table so as to have same contents as the first table when the contents of the corresponding piece of index information match the new contents of the corresponding piece of index information, and (ii) changing the first table so as to have same contents as the second table when the contents of the corresponding piece of index information are different from the new contents of the corresponding piece of index information. 
     With this construction, the need of the restoration processing can be easily judged by judging whether the index identifying information exists or not. The data updating apparatus then obtains the corresponding piece of index information, based on the address information, and changes one of the first table and the second table so as to have the same contents as the other in accordance with the result of comparing the contents of the corresponding piece of index information with the new contents of the corresponding piece of index information included in the index identifying information. Consequently, without comparing these tables with the storage state of the plurality of pieces of data, the restoration processing of the first table and the second table is performed. As a result, a restoration processing time is shortened. 
     The third object is achieved by a computer-readable storage medium that stores a data updating program to update a file in a storage medium which stores: (a) one or more files including the file to be updated, each of which includes a plurality of pieces of data, (b) a first table and a second table which both indicate a storage location of each piece of data and a sequence of the plurality of pieces of data of each file, and (c) one or more pieces of index information which are in a one-to-one correspondence with the one or more files and each associate a file name with a storage location of a predetermined piece of data of a file, the data updating program including the steps of: updating the first table, a piece of index information corresponding to the file to be updated, and the second table in the stated order in updating of the file; generating and writing index identifying information into the storage medium before the first table is updated, the index identifying information including (i) address information which shows a storage location of the corresponding piece of index information and (ii) new contents to which the corresponding piece of index information is to be updated; and deleting the index identifying information from the storage medium after the second table is updated. 
     With this construction, if restoration processing is to be performed when the index identifying information exists in the storage medium after the file updating results in incompletion, the need of restoration processing can be easily judged by judging whether the index identifying information exists or not. Accordingly, restoration processing can be started soon. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and the other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate a specific embodiment of the invention. 
     In the drawings: 
     FIG. 1 is a functional block diagram showing a conventional data updating apparatus; 
     FIG. 2 shows the relationship between the first FAT, the second FAT, the file indexes, and the data storage area of the conventional data updating apparatus; 
     FIG. 3 is a functional block diagram showing a data recording apparatus in an embodiment of the present invention; 
     FIG. 4 shows a logical structure of a first FAT, a second FAT, file indexes, and divided pieces of data stored in a storage unit of the data recording apparatus in the embodiment; 
     FIG. 5 shows a logical structure of a temporary index which is temporarily stored in the storage unit during data updating; 
     FIG. 6 is a flowchart showing data update processing performed by a recording control unit; and 
     FIG. 7 is a flowchart showing restoration processing performed in the storage unit. 
     FIG. 8 shows the states of old data, new data, a file index, a temporary index, the first FAT, and the second FAT after each step in the flowchart of the FIG.  7 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following describes a data recording apparatus in a preferred embodiment of the present invention with reference to the drawings. 
     &lt;Data Recording Apparatus&gt; 
     FIG. 3 is a functional block diagram showing a data recording apparatus  100  in the embodiment of the present invention. 
     The data recording apparatus  100  is an apparatus for reading/writing data and includes a recording control unit  101  which controls reading/writing of data and a storage unit  102  which stores the data. The data recording apparatus  100  also performs processing of restoring consistency when rebooting after data updating is interrupted. This processing is hereinafter called “restoration processing”. 
     Here, since the present invention is effective to update data stored in the storage unit  102  by changing or appending the data, the following description is limited to the updating of the data stored in the storage unit  102 . 
     The storage unit  102  is a storage medium such as a hard disc and has a storage area which is divided by sector and cluster. Each cluster is assigned a number to specify its physical storage location. 
     Also, the storage unit  102  stores a first FAT  121 , a second FAT  122 , file indexes  123 ,  124 ,  125 , . . . , and pieces of data  126 ,  127 ,  128 , . . . . 
     In addition, only during processing of updating the first FAT  121 , the second FAT  122 , the file indexes  123 ,  124 ,  125 , . . . (hereinafter called “update processing”), a temporary index  129  exists in the storage unit  102 . 
     The recording control unit  101  has a CPU and a storage medium such as a ROM (Read Only Memory) and is roughly made up of the following functional units: a data input/output control unit  103 , a first FAT updating unit  104 , a second FAT updating unit  105 , a file index updating unit  106 , a temporary index generating unit  107 , a temporary index deleting unit  108 , a data updating unit  109 , and a restoration processing control unit  110 . 
     The data input/output control unit  103  has a RAM storing data temporarily and controls input/output of the data in the storage unit  102 . For example, when receiving an instruction to update a file named “File1.doc” and data of the file used for updating (hereinafter called “update data”), the data input/output control unit  103  instructs the file index updating unit  106  to obtain a file index which shows the file name “File1.doc” and obtains the file index  123  from the file index updating unit  106 . 
     Also, the data input/output control unit  103  instructs the first FAT updating unit  104  to obtain the first FAT  121  and obtains the first FAT  121  from the first FAT updating unit  104 . After that, with reference to the file index  123  and the first FAT  121 , the data input/output control unit  103  recognizes numbers (cluster numbers) assigned to clusters which store existing divided pieces of data of the file named “File1.doc”, the sequence of the clusters which pointers indicate, namely data sequence, and available clusters. Then the data input/output control unit  103  calculates the number of clusters necessary to store the update data, allocates some more available clusters, and determines a new data sequence. 
     Moreover, the data input/output control unit  103  outputs (a) the cluster numbers and the data sequence (they are hereinafter called “FAT information”) to the first FAT updating unit  104 , (b) the FAT information and the update data to the data updating unit  109 , and (c) an updating instruction and the FAT information to the temporary index generating unit  107 . 
     When receiving the FAT information and the update data, the data updating unit  109  divides the update data by cluster and writes them into the clusters from the top divided piece in sequence in accordance with the FAT information. After completing writing all of the divided pieces of data, the data updating unit  109  outputs a notification that this writing has been completed (hereinafter called “data writing completion notification”, {circle around (1)} in FIG. 3) to the temporary index generating unit  107 . 
     Also, when receiving a notification that updating of the second FAT has been completed (hereinafter called “second FAT updating completion notification”, {circle around (5)} in FIG. 3) from the second FAT updating unit  105 , the data updating unit  109  deletes divided pieces of data which become unnecessary after the data updating and outputs a notification that this deleting has been completed (hereinafter called “data deleting notification”, {circle around (6)} in FIG. 3) to the temporary index deleting unit  108 . 
     When receiving the data deleting notification from the data updating unit  109 , the temporary index deleting unit  108  deletes the temporary index  129  from the storage unit  102 . This deleting is performed by changing a flag included in the temporary index  129  from 1 to 0 and clearing other information except the flag included in the temporary index  129 . The flag indicates that the temporary index  129  exists or not. 
     When receiving the data writing completion notification from the data updating unit  109 , the temporary index generating unit  107  generates a new temporary index  129  in accordance with the updating instruction and the FAT information which received from the data input/output control  103 , stores it in one sector of the storage unit  102  allocated specifically for storing the temporary index  129 , and outputs a notification that this storing has been completed (hereinafter called “storing completion notification”, {circle around (2)} in FIG. 3) to the first FAT updating unit  104 . 
     Since one sector is so small that storing in one sector is completed for a moment, it is not assumed that abnormality such as interruption of writing occurs. 
     The temporary index generating unit  107  also outputs this temporary index  129  to the file index updating unit  106 . 
     The first FAT updating unit  104  reads the first FAT  121  from the storage unit  102  in accordance with an instruction by the data input/output control  103  and outputs it to the data input/output control unit  103 . 
     Also, when receiving (a) the FAT information from the data input/output control unit  103  and (b) the storing completion notification from the temporary index generating unit  107 , the first FAT updating unit  104  updates the first FAT  121  stored in a first FAT storage area, based on the FAT information. Here, the first FAT storage area is a part of the storage area of the storage unit  102 , which is allocated specifically for storing the first FAT  121 . 
     Additionally, when receiving an instruction to write the second FAT  122  over the first FAT  121  from the restoration processing unit  113  in restoration processing, the first FAT updating unit  104  obtains the second FAT  122  in the storage unit  102  through the second FAT updating unit  105  and writes it into the first FAT storage area as the proper first FAT  121 . 
     Then, the first FAT updating unit  104  outputs a notification that this updating has been completed (hereinafter called “first FAT updating completion notification, {circle around (3)} in FIG. 3) to the file index updating unit  106 . 
     The file index updating  106  reads one file index from the storage unit  102  in accordance with an instruction by the data input/output control  103  and outputs it to the data input/output control unit  103 . 
     Next, when receiving the first FAT updating completion notification from the first FAT updating unit  104 , the file index updating unit  106  updates a file name, an entry cluster number, a data size, an attribute, and a time stamp (they are hereinafter called “index main items”) in the file index using the temporary index  129  which is received from the temporary index generating unit  107 . Then, the file index updating unit  106  outputs a notification that this updating has been completed (hereinafter called “file index updating completion notification”, {circle around (4)} in FIG. 3) to the second FAT updating unit  105 . 
     More specifically, when appending data, the file index updating unit  106  stores a corresponding file index in one of available sectors allocated specifically for storing file indexes in the storage unit  102 . On the other hand, when changing existing data, the file index updating unit  106  writes a new corresponding file index over the existing file index which shows the file name related to this data. 
     Here, in the same way as the temporary index generating unit  107 , since one sector is so small that writing into one sector is completed for a moment, it is not assumed that abnormality such as interruption of writing occurs. 
     When receiving the file index updating completion notification from the file index updating unit  106 , the second FAT updating unit  105  obtains the new first FAT  121  from the first FAT updating unit  104  and updates the second FAT  122  by writing the new first FAT  121  over the existing second FAT in a second FAT storage area as the new second FAT  122 . Here, the second FAT storage area is a part of the storage area of the storage unit  102 , which is allocated specifically for storing the second FAT  122 . 
     When receiving an instruction to write the first FAT  121  over the second FAT  122  from the restoration processing unit  113  in restoration processing, the second FAT updating unit  105  obtains the first FAT  121  in the storage unit  102  through the first FAT updating unit  104  and writes it into the second FAT storage area as the proper second FAT  122 . 
     Then, the second FAT updating unit  105  outputs the second FAT updating completion notification to the data updating unit  109 . 
     So far the update processing by the functional units such as changing or appending data is described. However, when just reading data of a file, the data input/output control unit  103  obtains the data of the file as the following. First the data input/output control unit  103  instructs the file index updating unit  106  to read a corresponding file index that shows a name of the file using the file name as a key to searching. Then the data input/output control unit  103  obtains the file index and recognizes a storage location of the top divided piece of data, based on the entry cluster number shown in the file index. Next, the data input/output control unit  103  instructs the first FAT updating unit  104  to read the first FAT  121  and obtains the first FAT  121 . Finally the data input/output control unit  103  traces clusters shown by pointers in the first FAT to read the data of the file from clusters. 
     The restoration processing control unit  110  includes a file index comparing unit  111 , a FAT comparing unit  112 , and a restoration processing unit  113 , and performs a restoration processing in rebooting of the data recording apparatus  100  after interruption of data updating. 
     The file index comparing unit  111  judges whether the temporary index  129  exists or not. 
     More specifically, the file index comparing unit  111  judges whether a predetermined bit (flag bit) is “1” or “0”. The flag bit is allocated specifically for storing the flag in the temporary index. When “1” is stored in the flag bit, the file index comparing unit  111  judges that the temporary index  129  exists; when “0” is stored in the flag bit, the file index comparing unit  111  judges that the temporary index  129  does not exist. 
     When the temporary index  129  does not exist, the file index comparing unit  111  outputs a notification of the result (hereinafter called “no existence notification”) to the restoration processing unit  113 . The no existence notification indicates that the temporary index  129  does not exist. 
     On the other hand, when the temporary index  129  exists, the file index comparing unit  111  reads this temporary index  129  and recognizes a storage location of a file index corresponding to the sector number shown in the temporary index  129 , for example, a storage location of the file index  123 . Then, the file index comparing unit  111  reads the file index  123  and judges whether the index main items shown in the temporary index  129  match the index main items shown in the file index  123 . 
     Then, when they match, the file index comparing unit  111  outputs a notification that they match (hereinafter called “index match notification”) to the restoration processing unit  113 , otherwise the file index comparing unit  111  outputs a notification that they do not match (hereinafter called “index mismatch notification”) to the restoration processing unit  113 . 
     The FAT comparing unit  112  reads the first FAT  121  and the second FAT  122  in accordance with an instruction by the restoration processing unit  113 . Then the FAT comparing unit  112  compares the contents of them and judges whether they match or not. When they match, the FAT comparing unit  112  outputs a notification that they match (hereinafter called “FAT match notification”) to the restoration processing unit  113 , otherwise the FAT comparing unit  112  outputs a notification that they do not match (hereinafter called “FAT mismatch notification”). 
     When receiving the index match notification or the index mismatch notification from the file index comparing unit  111 , the restoration processing unit  113  instructs the FAT comparing unit  112  to read the first FAT  121  and the second FAT  122 , compare the contents of them, and judge whether they match or not. Accordingly, the FAT comparing unit  112  receives the FAT match notification or the FAT mismatch notification. 
     On the other hand, when receiving the no existence notification from the file index comparing unit  111 , the restoration processing unit  113  judges that restoration processing is not necessary and ends the restoration processing. 
     If receiving a notification except the no existence notification, in other words, the index match notification or the index mismatch notification, the restoration processing unit  113  judges whether the notification from the FAT comparing unit  112  is the FAT match notification or the FAT mismatch notification. Then, if it is the FAT match notification, the restoration processing unit  113  instructs the temporary index deleting unit  108  to delete the temporary index  129 . 
     If the notification is the FAT mismatch notification, the restoration processing unit  113  judges whether the notification from the file index comparing unit  111  is the index match notification or the index mismatch notification. Then, if it is the index match notification, the restoration processing unit  113  instructs the first FAT updating unit  104  and the second FAT updating unit  105  to write the first FAT  121  over the second FAT  122 . 
     On the other hand, if the notification from the file index comparing unit  111  is the index mismatch notification, the restoration processing unit  113  instructs the first FAT updating unit  104  and the second FAT updating unit  105  to write the second FAT  122  over the first FAT  121 . 
     When receiving the data deleting notification from the data updating unit  109 , the temporary index deleting unit  108  deletes the temporary index  129  from the storage unit  102 . 
     &lt;Data&gt; 
     The following explains data stored in the storage unit  102  of the data recording apparatus  100  constructed as described above. 
     FIG. 4 shows a logical structure of the first FAT  121 , the second FAT  122 , file indexes  123 ,  124 ,  125 , . . . , and divided pieces of data  126 ,  127 ,  128 , . . . , stored in the storage unit  102 . 
     Each of the file indexes  123 ,  124 ,  125 , . . . , is a table which includes management information of a file. Since data structures of them are the same, only a data structure of the file index  123  is explained as an example. 
     A file name field  211  shows a name of a file related to the file index  123 , namely a file managed by the file index  123 . This file name is used as a search key. 
     An entry cluster number field  222  shows the number of a cluster that stores the top divided piece of data of the file. 
     A data size (KB) field  223  shows a total data size of all of the divided pieces of data included in the file in kilo bytes. 
     An attribute field  224  shows an attribute of the file, and the file attribute indicates whether the file admits to be written, or the like. 
     A time stamp field  225  shows a date and a time when the file index  123  was generated or updated. 
     The first FAT  121  and the second FAT  122  are tables obtained by duplexing a FAT. Therefore, except during update processing and after occurring abnormality in the update processing, their contents are the same. 
     Here a data structure of the first FAT  121  is explained as an example. 
     A cluster number column  241  shows a number which specifies a cluster, namely a cluster number. 
     When a divided piece of data is stored in the cluster specified by the corresponding field in the cluster number column  241 , a pointer column  242  shows a cluster number of a cluster storing a following divided piece of data. 
     At this time, if there is no following divided piece of data, the field in the pointer column  242  shows an End code to indicate that the following divided piece of data does not exist. 
     Here, if a cluster specified by the cluster number column  241  does not store a divided piece of data, the cluster does not store any data. 
     A data storage area  260  is a group of clusters. Each cluster is assigned to a number that specifies a storage location in the data storage area  260 . 
     The pieces of data  126 ,  127 ,  128 , . . . , are stored, based on storage locations and a data sequence shown in the first FAT and the second FAT. 
     FIG. 5 shows a logical structure of the temporary index  129  which is temporarily stored in the storage unit  102  during update processing. 
     The temporary index  129  has a similar data structure to the file index  123 ,  124 ,  125 , . . . , and includes the same contents of a new file index, namely index main items, and other management information. 
     First, the contents of the temporary index  129  are explained with showing the index main items. 
     A file name field  301  shows a name of the file, which is used after update processing. 
     An entry cluster number field  302  shows the number of a cluster that stores the top divided piece of data of the file. 
     A data size (KB) field  303  shows a total data size of all of the divided pieces of data included in the file in kilo bytes. 
     An attribute field  304  shows an attribute of the file, and the file attribute indicates whether the file admits to be written, or the like. 
     A time stamp field  305  shows a date and a time when the temporary index  129  was stored. 
     The above index main items are also used as the contents of the new file index. 
     Next, other pieces of information except the index main items are explained below. 
     A sector number field  306  and a flag field  307  are the added pieces of information. 
     When a target file index exists in the storage unit  102 , the sector number field  306  shows the number of the sector that stores the target file index. Here, the target file index is a file index which is being updated. 
     When a new file is generated, the sector number field  306  does not show anything. 
     The flag field  307  shows a flag “1” during update processing, which indicates update processing is being performed, otherwise the flag field  307  shows a flag “0”, which indicates update processing is not being performed. 
     Although the temporary index  129  is generated and stored in the storage unit  102  in each time of update processing, the existence of the temporary index  129  can be judged by checking only the flag bit. This is because the above contents from the file name to the flag are stored in each predetermined storage location in the storage unit  102 . 
     &lt;Update Processing&gt; 
     The following explains a data update processing performed by the recording control  101 . 
     FIG. 6 is a flowchart showing update processing of data stored in the storage unit  102  performed by the recording control unit  101 . 
     The data updating unit  109  divides update data by cluster and stores them in clusters from the top divided piece of data in accordance with FAT information. When completing storing all of the divided pieces of data, the data updating unit  109  outputs a data writing completion notification to the temporary index generating unit  107  (S 101 ). 
     When receiving the data writing completion notification, the temporary index generating unit  107  generates a new temporary index  129  corresponding to the update divided pieces of data, in accordance with an updating instruction and the FAT information which are received from the data input/output control unit  103 . Then, the temporary index generating unit  107  stores the temporary index  129  in the storage unit  102  and outputs a storing completion notification to the first FAT updating unit  104  (S 102 ). 
     When storing the temporary index  129  in the storage unit  102 , the temporary index generating unit  107  also outputs the temporary index  129  to the file index updating unit  106 . 
     Next, when receiving (a) the FAT information from the data input/output control unit  103  and (b) the storing completion notification from the temporary index generating unit  107 , the first FAT updating unit  104  updates the first FAT  121 , based on the FAT information. Then the first FAT updating unit  104  writes it into the first FAT storage area as the new first FAT  121  and outputs a first FAT updating completion notification to the file index updating unit  106  (S 103 ). 
     Moreover, when receiving the first FAT updating completion notification from the first FAT updating unit  104 , the file index updating unit  106  writes index main items shown in the temporary index  129  which is received from the temporary index generating unit  107  over the target file index, and outputs a file index updating completion notification to the second FAT updating unit  105  (S 104 ). 
     When receiving the file index updating completion notification from the file index updating unit  106 , the second FAT updating unit  105  obtains the first FAT  121 , which has been updated, through the first FAT updating unit  104  and updates the second FAT  122  by writing the first FAT  121  over the existing second FAT  122  as the new second FAT  122 . Then, the second FAT updating unit  105  outputs a second FAT updating completion notification (S 105 ). 
     When receiving the second FAT updating completion notification from the second FAT updating unit  105 , the data updating unit  109  deletes data which becomes unnecessary after the data updating and outputs a data deleting notification to the temporary index deleting unit  108  (S 106 ). 
     Furthermore, when receiving the data deleting notification from the data updating unit  109 , the temporary index deleting unit  108  deletes the temporary index  129  from the storage unit  102  (S 107 ) and ends the update processing. 
     &lt;Restoration Processing&gt; 
     The following explains restoration processing performed after the above update processing is interrupted by a power failure or the like. 
     FIG. 7 is a flowchart showing restoration processing performed by the recording control unit  101 . 
     When the data recording apparatus  100  is rebooted or has a system error, or the like, the file index comparing unit  111  judges whether the temporary index  129  exists or not in the storage unit  102  (S 201 ). When the temporary index  129  does not exist, the restoration processing is ended. 
     On the other hand, when the temporary index  129  exists, the FAT comparing unit  112  reads the first FAT  121  and the second FAT  122 , compares the contents of them, and judges whether they match or not (S 202 ). 
     When they match, the temporary index deleting unit  108  deletes the temporary index  129  from the storage unit  102 , and the restoration processing is ended. 
     When they do not match, the file index comparing unit  111  compares the contents of the temporary index  129  with the contents of the file index specified by a sector number shown in the temporary index  129 , which is the target file index (S 203 ), and judges whether their index main items match or not (S 204 ). 
     When their index main items match, the second FAT updating unit  105  writes the first FAT  121  over the existing second FAT  122  as the new second FAT  122  (S 205 ). Then, the temporary index deleting unit  108  deletes the temporary index  129  from the storage unit  102  (S 207 ), and the restoration processing is ended. 
     On the other hand, when their index main items do not match, the first FAT updating unit  104  writes the second FAT  122  over the existing first FAT  121  as the new first FAT (S 206 ). Then, the temporary index deleting unit  108  deletes the temporary index  129  from the storage unit  102  (S 207 ), and the restoration processing is ended. 
     FIG. 8 shows the states of old data, new data, a file index, a temporary index, the first FAT, and the second FAT after each of the above steps from S 101  to S 107 . Arrows show changes of the data or the like in restoring consistency from the state of them in each of the above steps. 
     In restoring consistency from the state in the step S 101 , the state of data or the like does not change, and the new data which has just stored for updating is left there. 
     In this way, the need of restoration processing can be easily judged by checking the flag bit in the temporary index  129 , and by checking the sector number of the temporary index  129 , the temporary index  129  can be compared with only the target file index without checking other file indexes. By comparing the first FAT  121  with the second FAT  122  in addition, a method of restoring, which is changing to the old state or changing to the new state, is determined without comparing all the contents of the first FAT with those of the second FAT. As a result, the restoration processing time is shortened. 
     Here, although the storage unit  102  is a storage medium such as a hard disc in the above embodiment of the present invention, a semiconductor memory, an optical magnetic disc, or the like may be used instead. 
     Also, although the sector number field  306  shows the number of a sector storing a target file index in the storage unit  102  in the above embodiment, the number of a cluster which includes the sector or a pass name which leads to the data stored in the sector may be used instead. 
     Moreover, the restoration processing can be performed by writing the proper contents over the improper contents without judging whether the contents of the first FAT and the second FAT match or not. 
     Furthermore, although the data recording apparatus  100  in the embodiment is used for the file system using a FAT and a file index, the present invention is effective to file systems using other databases as alternatives of the FAT and the file index such as NTFS (New Technology File System), in other word, a database which shows storage locations in a storage medium and a data sequence of divided pieces of data that form a file and a database which shows a file name and a storage location of the top divided piece of data of the file. 
     Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Therefore, unless such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.