Abstract:
A nonvolatile semiconductor storage device and method of managing the same are provided. The nonvolatile semiconductor storage device includes a nonvolatile memory configured to be electrically rewritable; and a controller configured to control an access area of the nonvolatile memory on the basis of information associated with management of the nonvolatile memory. The controller partitions an area of the nonvolatile memory for management and numbers management information for managing data for each area and a map of the management information in an integrated manner to write the numbered management information and map to the nonvolatile memory, thereby determining whether the management information and the map are normal on the basis of the numbering.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present application contains subject matter related to Japanese Patent Application JP 2007-025736 filed in the Japan Patent Office on Feb. 5, 2007, the entire contents of which is being incorporated herein by reference. 
     BACKGROUND 
     The present application relates to a nonvolatile semiconductor storage device, such as a flash memory, and a method of managing this nonvolatile semiconductor storage device. 
     Generally, in using a nonvolatile memory, management information, such as a logical-physical conversion table, is often created to relate the logical address of user data with the physical address in the nonvolatile memory and the created management information is used so as to prevent a particular area in the nonvolatile memory from being written excessively often and replace defect blocks, for example. It is also practiced to store this management information itself in the nonvolatile memory so as to save the time for reconfiguration at each power-on sequence, for example. 
     When user data is rewritten, the contents of the management information change, so that the correct reflection of a user data status onto the nonvolatile memory requires the rewriting of the management information in addition to the user data every time the rewriting of user data occurs. 
     SUMMARY 
     However, if the management information is rewritten every time, the processing time increases to lower the performance of the nonvolatile memory, so that rewriting of the management information is sometimes skipped. Because the management information cannot be written at the same time as the user data, an instance at which only the user data is rewritten occurs. For these reasons, a mismatch may take place between the user data and the management information in the nonvolatile memory due to a accidental power shutoff for example. 
     A method is proposed in which, in order to quickly check for a mismatch upon a system startup, the information indicative of the detection of no mismatch is written to the nonvolatile memory before the writing of the user data starts and, if the writing ends before the management information is updated, the information indicative of the end of the writing is written to the nonvolatile memory. At the time of startup, if that information is indicative of the timing after the start of rewriting, the correctness of the management information cannot be assured, so that the management information must be reconfigured. 
     However, the reconfiguration of the entire management information may take a lot of time depending on the storage capacity of the nonvolatile memory, thereby severely adversely affecting the system. 
     In an embodiment, the present application provides a nonvolatile semiconductor storage device and a method of managing the same that significantly shorten the time necessary for reconfiguring the management area of the nonvolatile semiconductor storage device and quickly make a decision whether the management information is valid or invalid. 
     In an embodiment, there is provided a nonvolatile semiconductor storage device. This nonvolatile semiconductor storage device has a nonvolatile memory configured to be electrically rewritable; and a controller configured to control an access area of the nonvolatile memory on the basis of information associated with management of the nonvolatile memory. The controller partitions an area of the nonvolatile memory for management and numbers management information for managing data for each area and a map of the management information in an integrated manner to write the numbered management information and map to the nonvolatile memory, thereby determining whether the management information and the map are normal on the basis of the numbering. 
     In another embodiment, there is provided a nonvolatile semiconductor storage device. This nonvolatile semiconductor storage device has a nonvolatile memory configured to be electrically rewritable; and a controller configured to control an access area of the nonvolatile memory on the basis of information associated with management of the nonvolatile memory. The controller manages the nonvolatile memory in a layered configuration, writes lower management information with a flag indicative of a status of the lower management information, and attaches information indicative of “old/new” for comparison between upper management information and the lower management information. 
     In still another embodiment, there is provided a method of managing a nonvolatile semiconductor storage device having a nonvolatile memory. The managing method includes partitioning an area of the nonvolatile memory for management thereof; integrally numbering management information for managing data for each area and a map for controlling the management information and writing the numbered management information and map to the nonvolatile memory; and determining whether the management information and the map are normal on the basis of the numbering. 
     In yet another embodiment, there is provided a method of managing a nonvolatile semiconductor storage device having a nonvolatile memory. The management method includes putting the nonvolatile memory into a layered structure for management; attaching a flag to lower management information to reflect a status thereof and writing the lower management information to the nonvolatile memory; and attaching information about old/new comparison between upper management information and the lower management information thereto and writing the upper management information and the lower management information to the nonvolatile memory. 
     According to an embodiment, an area is partitioned into sub areas to be managed and valid/invalid status of each sub area is determined, thereby limiting a range of reconfiguration, if necessary, to shorten the time necessary for the reconfiguration. In addition, management information is put in a layered structure and old/new status information is attached to each layered management information to quickly determine valid/invalid status of the management information for each sub area. 
     According to an embodiment, the processing and time required for configuring management information can be significantly reduced by improving the means for representing the status of management information in the nonvolatile memory system in which management information is stored in the nonvolatile memory, without significantly increasing the labor for checking the integrity of management information required at the time of a startup sequence and significantly increasing the frequency of writing management information. 
     This configuration can shorten the processing time required at the time of a startup sequence even in the nonvolatile memory system having a significantly increased total storage capacity, thereby realizing a further significant storage capacity increase in nonvolatile memory systems. 
     Additional features and advantages are described herein, and will be apparent from, the following Detailed Description and the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a schematic diagram illustrating an exemplary configuration of a memory system based on a nonvolatile semiconductor storage device practiced in an embodiment; 
         FIG. 2  is a schematic diagram illustrating a correlation between management information layers in an embodiment; 
         FIGS. 3A and 3B  are diagrams illustrating a manner in which management information is stored in a nonvolatile memory and this storage is represented, these figures being indicative of one erase block of a NAND flash memory for example; 
         FIGS. 4A and 4B  are first diagrams illustrating a manner in which management information is updated sequentially starting with the head of each block and this updating is represented; 
         FIGS. 5A and 5B  are second diagrams illustrating a manner in which management information is updated sequentially starting with the head of each block and this updating is represented; 
         FIGS. 6A and 6B  are third diagrams illustrating a manner in which management information is updated sequentially starting with the head of each block and this updating is represented; 
         FIGS. 7A and 7B  are fourth diagrams illustrating a manner in which management information is updated sequentially starting with the head of each block and this updating is represented; 
         FIGS. 8A and 8B  are first diagrams illustrating a manner in which the management information used up to a last page of the block is further updated and this updating is represented; 
         FIGS. 9A and 9B  are second diagrams illustrating a manner in which the management information used up to a last page of the block is further updated and this updating is represented; 
         FIGS. 10A and 10B  are diagrams illustrating a manner in which a map is stored in a nonvolatile memory and this storage is represented; 
         FIGS. 11A and 11B  are diagrams illustrating a manner in which map updating is made for the status of  FIG. 10 ; 
         FIGS. 12A and 12B  are diagrams illustrating a normal status of the map and the management information of the above-mentioned embodiment at the time of start up; 
         FIG. 13  is a first diagram illustrating a manner in which data is first written to area AR 1  after startup and the management information and the map in a nonvolatile memory are updated so as to reflect a most recent status; 
         FIG. 14  is a second diagram illustrating a manner in which data is first written to area AR 1  after startup and the management information and the map in a nonvolatile memory are updated so as to reflect a most recent status; 
         FIG. 15  is a third diagram illustrating a manner in which data is first written to area AR 1  after startup and the management information and the map in a nonvolatile memory are updated so as to reflect a most recent status; 
         FIG. 16  is a fourth diagram illustrating a manner in which data is first written to area AR 1  after startup and the management information and the map in a nonvolatile memory are updated so as to reflect a most recent status; 
         FIG. 17  is a fifth diagram illustrating a manner in which data is first written to area AR 1  after startup and the management information and the map in a nonvolatile memory are updated so as to reflect a most recent status; 
         FIG. 18  is a flowchart and a diagram indicative of a period of time in which the reflection of the map and the management information to be used for writing data to area AR 1  onto a most recent status of user data is assured; 
         FIG. 19  is a first diagram illustrating a manner in which user data in area AR 2  is rewritten from the status in which the management information in area AR 1  shown in  FIG. 16  is written, thereby writing the management information and the map; 
         FIG. 20  is a second diagram illustrating a manner in which user data in area AR 2  is rewritten from the status in which the management information in area AR 1  shown in  FIG. 16  is written, thereby writing the management information and the map; 
         FIG. 21  is a flowchart and a diagram indicative of a period of time in which the reflection of the map and the management information to be used for writing data to area AR 1  and area AR 2  onto a most recent status of user data is assured; 
         FIG. 22  is a first diagram illustrating a case in which user data is rewritten but the writing of a map becomes unnecessary; 
         FIG. 23  is a second diagram illustrating a case in which user data is rewritten but the writing of a map becomes unnecessary; 
         FIG. 24  is a flowchart indicative of checking and reconfiguration of management information and a map to be executed at the time of startup; 
         FIG. 25  is a diagram illustrating management information and a map in a nonvolatile memory at the time of startup following a power shutoff caused at a certain time; 
         FIG. 26  is a first diagram illustrating an example in which each area contains two or more pieces of management information; 
         FIGS. 27A and 27B  are second diagrams illustrating an example in which each area contains two or more pieces of management information; 
         FIGS. 28A and 28B  are third diagrams illustrating an example in which each area contains two or more pieces of management information; 
         FIG. 29  is a fourth diagram illustrating an example in which each area contains two or more pieces of management information; 
         FIG. 30  is a fifth diagram illustrating an example in which each area contains two or more pieces of management information; 
         FIG. 31  is a sixth diagram illustrating an example in which each area contains two or more pieces of management information; 
         FIG. 32  is a seventh diagram illustrating an example in which each area contains two or more pieces of management information; 
         FIG. 33  is an eighth diagram illustrating an example in which each area contains two or more pieces of management information; 
         FIG. 34  is a ninth diagram illustrating an example in which each area contains two or more pieces of management information; 
         FIG. 35  is a diagram illustrating an example in which the nonvolatile memory is large enough in storage size and therefore the management information in two or more areas can be expanded beforehand; 
         FIG. 36  is a diagram illustrating an example in which each area is partitioned into sub areas; 
         FIG. 37  is a first diagram illustrating a procedure of resetting ID to a smaller value; 
         FIG. 38  is a second diagram illustrating a procedure of resetting ID to a smaller value; 
         FIG. 39  is a third diagram illustrating a procedure of resetting ID to a smaller value; 
         FIG. 40  is a fourth diagram illustrating a procedure of resetting ID to a smaller value; 
         FIG. 41  is a first diagram illustrating manner in which the map and the management information of area AR 2  are updated in the nonvolatile memory in  FIGS. 37 through 40  above; 
         FIG. 42  is a second diagram illustrating manner in which the map and the management information of area AR 2  are updated in the nonvolatile memory in  FIGS. 37 through 40  above; 
         FIG. 43  is a third diagram illustrating manner in which the map and the management information of area AR 2  are updated in the nonvolatile memory in  FIGS. 37 through 40  above; and 
         FIG. 44  is a fourth diagram illustrating manner in which the map and the management information of area AR 2  are updated in the nonvolatile memory in  FIGS. 37 through 40  above. 
     
    
    
     DETAILED DESCRIPTION 
     The present application will be described in further detail by way of embodiments thereof with reference to the accompanying drawings. 
     Now, referring to  FIG. 1 , there is shown a schematic diagram illustrating an exemplary configuration of a memory system based on a nonvolatile semiconductor storage device practiced an embodiment. 
     A memory system  1  has at least one nonvolatile memory  2  (in the present embodiment, one nonvolatile memory is used), a controller  3 , and a host system  4  including a CPU. 
     The nonvolatile memory  2  has one or more nonvolatile memory banks. The nonvolatile memory  2  is made up of a NAND flash memory for example. The nonvolatile memory  2  may be one or more in quantity. User data, management information, and a map are stored in the nonvolatile memory  2 . An arrangement of these data and information in the nonvolatile memory  2  depends on a method in which the these data and information are managed. 
     The controller  3  is arranged between the host system  4  and the nonvolatile memory  2 ; to be more specific, a volatile memory  31  of the controller  3  is connected to the nonvolatile memory  2  and a logic section  32  in the controller  3  is connected to the host system  4  via a host interface. Thus, the volatile memory  31  and the logic section  32  are arranged in the controller  3 . The volatile memory  31  stores a map and a part or all of management information read from the nonvolatile memory  2  in an expanded manner. When data is rewritten, the controller  3  updates the information thereof in the volatile memory  31  and then writes the updated information to the nonvolatile memory  2 . 
     It should be noted that the controller  3  may be incorporated in the host system  4 . In this case, the nonvolatile memory  2  is directly connected to the host system  4 . If the controller  3  is incorporated in the host system  4 , the logic section  32  may be software that operates on the CPU of the host system  4 . In this case, there occurs an advantage of eliminating the necessity of dedicated hardware. Also, the volatile memory  31  may be shared by a volatile memory of the host system  4 . In this case, there occurs an advantage of saving the number of memories. 
     Thus configured, in the management of the nonvolatile memory  2 , such as a flash memory, by adding information indicative of relative “old/new” to each piece of layered management information, the memory system  1  can determine whether upper information correctly reflects lower information. 
     Further, updating the lower management information before writing user data allows the determination that the management information is correct as the whole system if the upper management information can correctly reflect the lower management information. 
     Referring to  FIG. 2 , there is shown a correlation between pieces of layered management information in the present embodiment. 
     In the present embodiment, as shown in  FIG. 2 , a user data UD area is partitioned into two or more areas AR 1  through ARm (m=4 in the example shown in  FIG. 2 ) and each of these areas is provided with management information CINF, such as a logical-physical conversion table. 
     A map MP is also provided for the management of management information CINF. The address of the management information CINF on the nonvolatile memory  2  is recorded to the map MP beforehand and this map MP is stored in the nonvolatile memory  2  at a location easy to search for. This arrangement allows the quick locating of the map and the management information recorded with the address after each startup sequence. 
     The partitioning of user data UD area may be made by any means, such as physical address or logical address. Also, the management information may be provided in two or more systems, such as the management information for physically partitioned areas and the management information for logically partitioned areas, for example. 
     This multiple system approach is advantageous in that the proper partitioning is allowed in accordance with the contents to be managed, such as the logical partitioning is more efficient for the logical-physical table but the physical partitioning is more efficient for the table indicative of block status, for example. If two or more systems of management information are used, it is required to determine whether the management information about particular data is correct or not by all the systems associated with that particular data. 
       FIGS. 3A and 3B  show a example of how management information is stored in the nonvolatile memory and how this storage is represented. 
       FIG. 3A  shows one erase block in an NAND flash memory, for example, this block containing 64 pages, each providing a write unit. One page PG has a redundant part RDNP in addition to a data part DTP. Management information CINF has, in redundant part RDNP, ID indicative of “old/new” and fields IDFLD and WRFLD indicative of “under writing/not under writing”. 
     In block BLK, data is written in the ascending order of page numbers, only the contents of the page written last being valid. This is expressed by  FIG. 3B , only the valid information being used. 
       FIGS. 12A and 12B  and so on use the expression shown in  FIG. 3B  as the expression of the management information in the nonvolatile memory. 
       FIGS. 4A and 4B  through  FIGS. 7A and 7B  show manners in which management information is updated starting from the head of block and manners of expressing the updating. 
       FIG. 4A  shows a status in which management information CINF is written to page PG 0  that is the start page of block.  FIG. 4B  shows the expression thereof. 
     If management information CINF is updated from this status, the data to be updated is written to PG 1  that is the page next to PG 0  containing valid data as shown in  FIG. 5A . In doing so, the information appropriate at that time is written to redundant part RDNP.  FIG. 5B  shows an updated status, in which ID and fields IDFLD and WRFLD are updated to those of PG 1 . 
       FIGS. 6A and 6B  show a status in which the status shown in  FIGS. 5A and 5B  are updated. As shown in  FIG. 6A , data part DTP and redundant part RDNP are written to page PG 2  next to the page PG 1  containing valid data.  FIG. 6B  shows an updated status.  FIGS. 7A and 7B  shows a further updated status. 
       FIGS. 8A and 8B  and  FIGS. 9A and 9B  show the manners in which the management information used up to the last page of block is further updated and manners of expressing this updating. 
       FIG. 8A  shows a status in which data is written up to page PG 6  that is the last page of block, data part DTP and redundant part RDNP being valid.  FIG. 8B  shows this status, the valid information being used. 
       FIG. 9A  shows a manner in which management information is updated for the status shown in  FIG. 8A . First, a free block other than the block in use is allocated and update data and a redundant part are written to PG 0  that is the start page of the allocated block. Next, the block used so far is erased. Consequently, the block written with valid data to page PG 0  remains.  FIG. 9B  expresses an updated status. Because this expression does not include the information indicative up to which page the block has been used,  FIG. 9B  shows the same change as others as simply the valid data has been updated. 
       FIGS. 10A and 10B  show a manner in which a map is stored in the nonvolatile memory and a manner of expressing this storage. 
       FIG. 10A  is representative of one erase block in the nonvolatile memory  2 , in which 64 pages are contained as write unit. One page PG contains redundant part RDNP in addition to data part DTP, map MNP having ID indicative of “old/new” in redundant part RDNP. 
     Management information CINF has a field indicative of “under writing/not under writing”; however, no information is allocated that area in map MP. In block BLK, data is written in the ascending order of page numbers, the contents of the page written last being valid. So,  FIG. 10B  expresses only the valid information. Unlike management information, only data part DTP and ID are expressed.  FIGS. 12  and so on uses the expression of  FIG. 10B  as the expression of map MP in the nonvolatile memory  2 . 
       FIGS. 11A and 11B  show a status in which map updating has been made for the status shown in  FIGS. 10A and 10B . 
       FIG. 11A  shows the status in which valid data is contained in page PG 4  and new data is written to page PG 5  next to page PG 4 . In doing so, the information appropriate at that time is written to redundant part RDNP. 
       FIG. 11B  expresses an updated status, in which ID is that of updated page PG 5 . 
       FIGS. 12A and 12B  show an example of a normal status at the time of a startup sequence of the map and management information of the present embodiment. 
     The nonvolatile memory  2  stores the map MP of management information CINF and the management information CINF corresponding to each of partitioned areas. The management information CINF contains ID indicative of “old/new” and fields IDFLD and WRFLD indicative of “under writing/not under writing”. 
     In this example, a status indicative of “under writing” is indicated by 0x1 and a status indicative of “not under writing” is indicated by 0x0. The map MP also contains an ID field indicative of old/new. 
     Management information CINF and map MP may be located anywhere in the nonvolatile memory  2 . If the ID of map MP has a number higher than the ID of management information CINF, it indicates that the information of map MP is newer than management information CINF, thereby reflecting the most recent status of management information CINF. 
     In the initial status, ID is 0x1 in all management information CINF and maps and there is no management information CINF having data indicative of “under writing”. In this status, all management information CINF in the nonvolatile memory  2  reflects the most recent status of data and map MP also reflects the most recent status of all management information CINF. In the initial status, no data is expanded in the volatile memory  31 . 
       FIGS. 13 through 17  show operations in which data is written to area AR 1  first upon a startup sequence and the management information and the map in the nonvolatile memory are updated so as to reflect the most recent status. 
       FIG. 13  an operation in which, when request to write data to area AR 1  is made, map MP and management information CINF are expanded from the nonvolatile memory  2  into the volatile memory  31 . 
     Map MP may be expanded into the volatile memory  31  only once first after each startup sequence. By referencing map MP in the volatile memory  31 , management information CINF is read from area AR 1  into the volatile memory  31 . In this status, management information CINF and map MP in the nonvolatile memory  2  still reflect the most recent status of user data UD and management information CINF. 
       FIG. 14  shows an operation in which, before actually rewriting user data UD, writing to management information CINF in area AR 1  is executed. To management information CINF to which writing is executed, 0x2 is set as a number greater than 0x1 that is the ID of map MP and a status of “under writing” is set as the information indicative of “under writing/not under writing”. 
     In a status in which management information CINF has only been written, management information CINF actually reflects the most recent status of user data UD. 
     However, because the ID of management information CINF becomes greater than the ID of map MP, that the information of map MP reflects the most recent status of management information CINF cannot be assured and, because the status of “under writing” is set to the management information, that management information CINF reflects the most recent status of the user data cannot be assured. Hence, if a power shutoff occurs subsequently, management information CINF and map MP must be reconfigured at the time of a next startup sequence. 
       FIG. 15  shows a relationship of management information while user data US is being actually rewritten. Along with the rewriting of user data, management information CINF and map MP are updated in the volatile memory  31 . Consequently, management information CINF in the nonvolatile memory  2  will not reflect the most recent user data UD. 
       FIG. 16  shows an operation in which, after rewriting user data UD, management information CINF in area AR 1  is written. When user data UD has been written, management information CINF is written last as a status of “not under writing”. The ID at this moment is the same as the ID so far. 
     Consequently, management information CINF in the nonvolatile memory  2  comes to reflect the most recent user data. However, map MP in the nonvolatile memory  2  does not reflect the most recent management information CINF. 
       FIG. 17  shows an operation in which map writing is executed after management information has been written. When the writing of management information CINF has been completed and the management information CINF in the nonvolatile memory  2  comes to reflect the most recent user data UD, map MP is written to the nonvolatile memory  2 . At this moment, ID is a number equal to or greater than the maximum value (0x2 in this example) of the ID of management information CINF, namely, 0x2. 
     Consequently, the map in the nonvolatile memory  2  comes to reflect the most recent management information CINF. In this status, the ID of the map in the nonvolatile memory  2  becomes equal to or greater than the maximum value (the same value in this example) of the ID of all management information in the nonvolatile memory  2 , thereby assuring that the map MP in the nonvolatile memory  2  reflects the most recent status of all management information CINF. 
     In addition, because management information CINF is written before rewriting user data, if map MP in the nonvolatile memory  2  reflects the most recent status of management information CINF, it can be assured that management information CINF also reflects the most recent status of user data UD, which in turn assures that all information reflects the most recent status. 
       FIG. 18  shows a period of time in which it can be assured that the map and the management information at the time of writing to area AR 1  reflect the most recent status of management information and user data. In  FIG. 18 , each white arrow is indicative of a period of time in which it can be assured that redundant part RDNP in the nonvolatile memory  2  reflects the most recent status, while each black arrow is indicative of a period of time in which the map MP/management information CINF in the nonvolatile memory  2  actually reflect the most recent status. 
     In  FIG. 18 , when management information CINF is first written (ST 1 ), it cannot be assured that map MP reflects the most recent status of management information CINF and, when the rewriting of user data starts (ST 2 ), management information CINF does not reflect the most recent status of user data. 
     However, when management information CINF is written with “under writing” status set, it cannot be assured that management information CINF does not reflect the most recent status of user data. When, after the rewriting of user data, management information CINF is written as “not under writing” (ST 3 ), management information CINF in the nonvolatile memory  2  reflects the most recent status of user data UD, thereby assuring that the recent status is actually reflected. Also, when map MP has been written (ST 4 ), map MP in the nonvolatile memory  2  comes to reflect the most recent status of management information CINF, thereby assuring that the most recent status is actually reflected. 
       FIGS. 19 and 20  show manners in which the user data in area AR 2  is rewritten from the status in which management information is written to area AR 1  shown in  FIG. 16 , thereby writing management information and maps. 
       FIG. 19  shows a manner in which after rewriting user data UD and writing management information CINF to area AR 1 , user data is written to area AR 2  without writing map MP. 
     User data UD can be rewritten to another area without writing to map MP. This is advantageous in that the speed of processing is enhanced and the life of map writing area is lengthened by reducing the number of times map MP is written. 
     Before writing user data UD to area AR 2 , the ID of management information CINF is set to a number greater than the ID of map MP (0x2 in this example) and then the user data is written by setting “under writing” status, as with area AR 1 . 
     Also, the expansion and saving of other management information CINF with area AR 2  are executed as required. In this status, the ID of management information CINF is greater than the ID of map MP for area AR 1  and area AR 2 . Hence, map MP in the nonvolatile memory  2  does not reflect the most recent status of management information CINF. As for area AR 2 , “under writing” status is set, thereby denoting that management information CINF in the nonvolatile memory  2  does not reflect the most recent status of user data UD. 
       FIG. 20  shows a manner in which, after rewriting user data UD to area AR 2 , management information CINF and map MP are written. 
     After rewriting user data UD to area AR 2 , management information CINF is written last as “not under writing” status. The ID at this point of time is the same as before. Consequently, as with area AR 1 , management information CINF in the nonvolatile memory  2  comes to reflect the most recent status of user data UD. Then, when map MP is written, map MP in the nonvolatile memory  2  comes to reflect the most recent status of management information CINF for all areas. 
     It should be noted that, if a configuration is made so as to finally write map MP, data can be written to other areas AR without writing map MP. If the frequency of writing map MP is reduced, the time necessary for the writing can be shortened and the number of time rewriting is made can be reduced. 
     On the other hand, of the map MP in the nonvolatile memory  2 , parts that do not reflect the most recent status of management information CINF increase, so that a range that must be reconfigured after a power shut-off sequence is widened. 
       FIG. 21  shows a period of time in which it can be assured that the map and management information at the time of writing to area AR 1  and area AR 2  reflect the most recent status of management information and user data. 
     In the figure, each arrow denotes the same as in  FIG. 20 . As for management information CINF, a period of time in which it cannot be assured that the most recent status of user data is reflected ranges from a time (ST 11 ) at which the management information in that area was written with “under writing” status set to a time (ST 12  to ST 16 ) at which management information is written with “not under writing” after rewriting user data. These periods of time hold true with both area A 1  and area A 2 . 
     As for map MP, a period of time in which it cannot assured that the most recent status of management information CINF in that area is reflected ranges from a period at which the management information CINF in that area was written to a time at which map MP is finally written (ST 17 ). In this case, even after starting the rewriting of area AR 2  after the rewriting of area AR 1 , it cannot be assured that the map reflects the most recent status of management information for area AR 1 . 
       FIGS. 22 and 23  show examples in which user data rewritten but the writing of a map is not required. 
       FIG. 22  shows a status in which user data UD is rewritten for area AR 1  from the initial status shown in  FIG. 13 . It should be noted that the elements managed by map MP are not changed for the writing of management information CINF; actually, map MP in the nonvolatile memory  2  reflects the most recent information of management information CINF. 
       FIG. 23  shows a manner in which map MP and management information CINF in the nonvolatile memory  2  reflect the most recent status of management information CINF and user data UD only by the writing of management information from the status shown in  FIG. 22 . 
     For the status shown in  FIG. 22 , the same ID (0x1 in this example) as that of map MP is used at writing the last management information CINF and this management information is written as “not under writing”, thereby determining that the map MP in the nonvolatile memory  2  reflects the most recent status of management information CINF. 
     It should be noted, however, that this writing of the last management information CINF is limited to the case in which map MP need not be changed. Consequently, the frequency of map writing can be purely reduced. 
       FIG. 24  shows flows of the checking and reconfiguration of management information and a map to be executed at the time of a startup sequence. 
     At the time of a startup sequence, all management areas are checked. For all management areas, the ID of map MP is compared with the ID of management information (ST 21  through ST 27 ). If the ID of map MP is higher than the ID management information CINF, it can be determined that, for that area, map MP reflects the most recent management information CINF and management information CINF reflects the most recent user data UD. In this case, the reconfiguration of the map and management information of that area is not required (ST 23 ). 
     If the ID of map is lower than the ID of management information, then it indicates that the power has been shut off with no map requiring updating written after the writing of management information. In this case, a field indicative whether management information is under writing is checked (ST 24 ); if management information is found under writing, the reconfiguration of the management information is required by actual use of user data for that area (ST 25 ). 
     It should be noted that, regardless of “under writing” or “not under writing”, the map must be reconfigured for that area (ST 26 ). 
       FIG. 25  shows the management information and map in the nonvolatile memory at the time of a startup sequence that takes place after a power shutoff at a certain time. 
     In this status, the ID of map MP being 0x1 and the ID of management information CINF in area AR 1  being 0x2 provide “not under writing” status, the ID of management information CINF in area AR 2  being 0x2 provide “under writing” status and the ID of management information CINF in other areas AR being 0x1 provides “not under writing” status. 
     In this case, for area AR 1 , a part corresponding to that area of map MP must be reconfigured; for area AR 2 , both management information CINF and the part corresponding to that area of map MP must be reconfigured. 
     For other areas, neither management information CINF nor the part corresponding to that area of map MP need be reconfigured. 
     It should be noted that, for area AR 1  and area AR 2 , map MP does not reflect the most recent status of management information CINF, so that the location of the management information CINF obtained by map MP may not be correct. In this case, it is also required to search the nonvolatile memory  2  for management information CINF. 
       FIGS. 26 through 34  show examples in which there are two or more pieces of management information in each area. 
       FIG. 26  shows a manner in which there are two or more pieces of management information CINF in each area in the volatile memory  31  and in the nonvolatile memory  2 . Here, of the two or more pieces of management information CINF, one representative piece of management information is provided with and fields IDFLD and WRFLD indicative of ID and “under writing/not under writing”, the other management information CINF being not provided with these fields. 
       FIGS. 27A and 27B  show a manner in which non-representative management information CINF is stored in the nonvolatile memory  2  and a manner of this storage. 
       FIG. 27A  is indicative of one erase block in the nonvolatile memory  2 , in which 64 pages, each being a write unit, are included. One page PG contains a redundant part RDNP in addition to a data part DTP. With non-representative management information CINF, information allocation to ID and fields indicative of “under writing/not under writing” is not executed. 
     In block BLK, data is written in the ascending order of page numbers, only the contents of page written last being valid. This is represented by  FIG. 27B  by use of only the valid information. Unlike the representative management information CINF, only the data part is represented. In  FIGS. 29  and so on, this expression of  FIG. 27  is used as the expression of non-representative management information in the nonvolatile memory. 
       FIGS. 28A and 28B  show a manner in which non-representative management information has been updated for the status shown in  FIGS. 27A and 27B . In  FIG. 27A , valid data is contained in page PG 4  and, as shown in  FIG. 28A , new data is written to page PG 5  that follows page PG 4 .  FIG. 28B  shows the expression of an updated status, in which no valid information is contained in the redundant part. 
       FIG. 29  shows an example of a normal status at the time of a startup sequence of map MP and management information CINF in an embodiment in which one area has two pieces of management information CINF. 
     The nonvolatile memory  2  stores two or more pieces of management information CINF corresponding to the map MP of management information CINF and partitioned areas. 
     Management information CINF representative for each area has fields IDFLD and WRFLD indicative of “old/new” and “under writing/not under writing”. Here, “under writing” status is indicated by 0x1 and “not under writing” status is indicated by 0x0. 
     The non-representative management information CINF has no ID and no field indicative of “under writing/not under writing”. Map MP also has an ID field indicative of “old/new”. Management information CINF and map MP may be located anywhere in the nonvolatile memory  2 . If the ID of map MP has a number higher than that of the ID of management information CINF, it indicates that the information of map MP is more recent than management information CINF, reflecting the most recent status of management information CINF. 
     In the initial status, the ID is 0x1 for the management information CINF and map MP representing all and there is no management information CINF having data indicative of “under writing”. In this status, all management information CINF in the nonvolatile memory  2  reflect the most recent status of data and the map MP also reflects the most recent status of all management information CINF. It should also be noted that none of the data is expanded in the volatile memory  31 . 
       FIG. 30  through  FIG. 34  show a status in which data is written to area  1  first after a startup sequence and management information CINF and map MP in the nonvolatile memory  2  are updated so as to reflect the most recent status. 
       FIG. 30  shows an operation in which, when a request for writing to area AR 1  is made, map MP and representative management information CINF are expanded from the nonvolatile memory  2  into the volatile memory  31 . 
     The expansion of map MP from the nonvolatile memory  2  into the volatile memory  31  may be made only once after a startup sequence. By referencing the map in the volatile memory  31 , the representative management information in the area AR 1  is read into the volatile memory  31 . 
     In this status, the management information CINF and the map MP in the nonvolatile memory  2  still reflect the most recent status of user data UD and management information CINF. 
       FIG. 31  shows an operation in which, before user data UD is actually rewritten, data is written to the management information CINF representative of area AR 1 . 
     To the management information CINF to be written with data, 0x2 that is a number greater than 0x1 that is the ID of map MP is set as ID and a status indicative of “under writing” is set as the information indicative of “under writing/not under writing”. 
     In the status in which only the representative management information CINF has been written, management information CINF actually reflects the most recent status of user data UD, but, because the ID of management information CINF becomes greater than the ID of map MP, it cannot be assured that the information of map MP reflects the most recent status of management information CINF, which, in turn, cannot assure that management information CINF reflects the most recent status of user data because “under writing” status is set to the representative management information CINF. 
     Hence, if a power shutoff occurs subsequently, management information CINF and map MP must be reconfigured at a next startup sequence. 
       FIG. 32  shows a relationship of management information CINF during a period of time in which user data UD is actually being rewritten. 
     At the same time user data UD is rewritten, management information CINF and map MP are updated in the volatile memory  31 . Consequently, the management information CINF in the nonvolatile memory  2  will not reflect the most recent user data UD. 
     For the management information CINF other than the representative management information CINF, the nonvolatile memory  2  may be rewritten without restriction like user data. 
       FIG. 33  shows an operation in which, after user data UD is written, the management information CINF representative of area AR 1  is written. 
     After saving all other management information CINF in the same area into the nonvolatile memory  2  after the rewriting of user data UD, the representative management information CINF is written as “not under writing” status. The ID at this moment is the same as before. 
     Consequently, the management information CINF in the nonvolatile memory  2  comes to reflect the most recent user data UD. However, the map MP in the nonvolatile memory  2  does not reflect the most recent management information CINF. 
       FIG. 34  shows an operation in which map MP is written after management information CINF has been written. 
     When, after the writing of management information CINF, the management information CINF in the nonvolatile memory  2  comes to reflect the most recent user data UD, map MP is written to the nonvolatile memory  2 . The ID at this moment is 0x2, the same as the maximum value (0x2 in this example) of the representative management information CINF. 
     Consequently, the map MP in the nonvolatile memory  2  comes to reflect the most recent management information CINF. In this status, the ID of map MP in the nonvolatile memory  2  takes a value (the same value in this example) greater than the maximum value of the ID of all representative management information CINF in the nonvolatile memory  2 , so that it can be assured that the map MP in the nonvolatile memory  2  reflects the most recent status of all management information CINF. 
     Further, because the representative information CINF is written before rewriting user data UD, if the map MP in the nonvolatile memory  2  reflects the most recent status of management information CINF, it can be assured that management information CINF also reflects the most recent status of user data UD, thereby assuring that all information reflects the most recent status. 
       FIG. 35  shows an example in which the volatile memory has a memory space large enough for the expansion of the management information of two or more areas. 
     If the volatile memory  31  has a memory space large enough for the expansion of the management information CINF of two or more areas, then it is practicable to provide two or more areas that are handled as “under writing” by setting “under writing” status to management information CINF and writing data thereto. 
     This configuration is advantageous that, if writing is executed by making access between two or more areas for example, the expansion and save of management information CINF need not be executed every time. 
     The expansion of management information CINF of two or more areas requires, in writing map MP, to put, into a written status, the management information in “not under writing” in all areas and then write the map having the ID equal to or greater than the maximum value of the ID of all management information. 
     Consequently, in the area with the ID of management information CINF being lower than the ID of map MP, the map MP in the nonvolatile memory  2  also reflects the most recent status of management information CINF. 
       FIG. 36  shows an example in which each area is further partitioned into sub areas. 
     Each area is partitioned into sub areas including management information CINF; however, the ID to be attached to management information CINF and fields IDFLD and WRFLD indicative of “under writing/not under writing” are attached to each area before being partitioned one for one. It should be noted that the field WRFLD indicative of “under writing/not under writing” must take a form to tell which of sub areas is under writing. 
     In  FIG. 36 , of four sub areas, only one is handled as “under writing” and the number of this sub area is used to indicate that this sub area is under writing. It is also practicable to prepare flags corresponding to the number of sub areas to individually indicate whether each sub area is under writing or not. The partitioning into sub areas allows the determination for each sub area whether the most recent status of user data UD is reflected for management information CINF, thereby narrowing a target range of reconfiguring management information CINF. 
     Consequently, the time required for reconfiguring management information CINF can be shortened without involving the labor for determining the integrity between map and management information CINF based on ID comparison. If it is configured that the flag indicative of “under writing” of each sub area shows this status for each sub area, an advantage is provided that two or more sub areas can be handled as “under writing”, at the cost of increasing the number of sub areas to be reconfigured.  FIG. 37  through  FIG. 40  show a procedure of resetting the ID to a smaller value. 
       FIG. 37  shows a status of management information CINF and map MP at a particular stage. In this example, the ID of map MP is 0xFE, the ID of area AR 1  is 0xFE, the ID of area AR 2  is 0xF0, and the ID of area ARm is 0x58. The ID takes a larger value as the writing is made to management information CINF and map MP; however, only values in a limited range can be recorded to the nonvolatile memory  2 . Therefore, it is required to reset the value to a smaller one when the value gets fairly large. 
       FIG. 38  shows a status in which the map is written with an ID, a special minimum value 0x0, attached. At this point of time, the contents of map MP in the nonvolatile memory  2  reflect the most recent status of management information CINF; however, the ID is in the status not assuring the contents of map MP, so that, if a power shutoff for example occurs at this stage, map MP must be reconfigured for all areas. 
       FIG. 39  shows a status in which 0x1 is attached to the management information CINF of all areas as ID. 
     Because management information CINF is written, the updating of map MP may be required, so that the map MP in the nonvolatile memory  2  does not always reflect the most recent status of management information CINF. However, because map MP is written with ID of 0x0, no error recognition occurs that the most recent status is reflected. 
       FIG. 40  shows a status in which map MP is attached with 0x1 that is the same as the maximum value of the ID of management information CINF and data is written to that map MP. The map in the nonvolatile memory  2  reflects the most recent status of management information. Consequently, the resetting of ID to a smaller value has been completed. 
       FIG. 41  through  FIG. 44  show a manner in which the map and the management information in area AR 2  are updated in each of  FIG. 37  through  FIG. 40 . 
       FIG. 41  shows a status of the map MP in the nonvolatile memory  2  the management information CINF in area AR 2  shown in  FIG. 37 . The map MP and the management information CINF are written in halfway pages of separate blocks as valid data. 
       FIG. 42  shows a status of the map in the nonvolatile memory  2  and the management information CINF in area AR 2  shown in  FIG. 38 . The map is updated with ID=0x0 for the status shown in  FIG. 41 ; in the nonvolatile memory  2 , the map is written to a page with ID=0x0 next to a page of ID=0xFE in the nonvolatile memory  2  for area AR 2  for example. 
       FIG. 43  shows a status of the map in the nonvolatile memory  2  and the management information CINF in area AR 2  shown in  FIG. 39 . 
     Each management information CINF is updated with ID=0x1 for the status shown in  FIG. 42 ; in the nonvolatile memory  2 , the map is written to a page with ID=0x1 next to a page of ID=0xF0 in the nonvolatile memory  2  for area AR 2  for example. 
       FIG. 44  shows a status of the map in the nonvolatile memory  2  and the management information CINF in area AR 2  shown in  FIG. 40 . The map is updated with ID=0x1 for the status shown in  FIG. 43 ; in the nonvolatile memory  2 , the map is written to a page with ID=0x1 next to a page of ID=0x0 in the nonvolatile memory  2 . 
     As described above and according to an embodiment, the processing and time required for configuring management information CINF can be significantly reduced by improving the means for representing the status of management information CINF in the nonvolatile memory system  1  in which management information CINF is stored in the nonvolatile memory  2 , without significantly increasing the labor for checking the integrity of management information CINF required at the time of a startup sequence and significantly increasing the frequency of writing management information CINF. 
     This configuration can shorten the processing time required at the time of a startup sequence even in the nonvolatile memory system  1  having a significantly increased total storage capacity, thereby realizing a further significant storage capacity increase in nonvolatile memory systems. 
     It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.