Electrical computers and digital processing systems: memory – Storage accessing and control – Specific memory composition
Reexamination Certificate
2000-04-18
2002-11-05
Kim, Matthew (Department: 2186)
Electrical computers and digital processing systems: memory
Storage accessing and control
Specific memory composition
C711S103000, C711S209000
Reexamination Certificate
active
06477616
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a data processing system using a computer usable recording medium, and a computer readable recording medium storing a program for accessing the recording medium.
2. Description of the Related Art
A flash memory employing an EEPROM (Electrically Erasable/Programmable Read Only Memory) has been used as a recording medium to be accessed (data write/erase possible) by a computer and the like. In the flash memory, erasure of data is performed in the unit, generally so-called blocks, of the storage capacity.
Defective blocks cause unsuccessful data writing. However, it is difficult to avoid such defective blocks from appearing during manufacturing process for producing a flash memory, especially a NAND type flash memory. A conventional solution for such a problem is an address conversion table. The address conversion table represents a correspondence between at least one physical address and at least one logical address. The address conversion table is prepared by dynamically assigning successive logical addresses to normal blocks, while the physical address has been assigned to each block. Thus prepared address conversion table prevents any procedure for externally-arrived access from being complicated, resulting in addresses being successive.
In a case where the address conversion table represents a correspondence between all logical and physical addresses, size of the address conversion table is proportionate to storage capacity of the flash memory. Therefore, the large flash memory requires a large storage device for storing the enlarged table. As a result, the storage device has the complicated structure.
Zoning is a known solution to avoid the storage device from being complicated. According to this method, the plurality of block are classified into a plurality of zones. The address conversion table is prepared so as to represent the correspondence between logical and physical addresses which belong to one of the zones. If any demand for accessing the blocks in another zone is given, the table is reformed so as to include the logical and physical addresses in the zone concerned.
Since such a table reformation requires an extra process for searching all the blocks in the zone concerned, its processing time is elongated. If the flash memory is under the control of OS (Operating System), the OS usually writes FAT (File Allocation Table) or the like onto the flash memory. The FAT represents a correspondence between data managed by the OS and logical addresses thereof. An access procedure to such an extra table also requires an address conversion table. Therefore, further extra processing for preparing the address conversion table for FAT elongates the processing time further.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above. It is an object of the present invention to provide a storage device, a storage system and a memory management method that reduce frequency for preparing address conversion tables when accessing data.
In order to achieve the above-described object, according to the first aspect of the present invention, there is provided a storage device, comprising: a memory which includes a plurality of memory blocks, each of which stores data and belongs to one of a plurality of zones and to each of which a physical address is assigned; and a controller which reads data stored in the plurality of memory blocks and externally outputs the read data, wherein the memory block belonging to a predetermined zone includes a data arrangement memory storing a data arrangement table representing a correspondence between data stored in the memory and a logical address of one memory block storing the data, and the controller includes a first table memory, includes a second table memory, creates a first address conversion table storing information representing a correspondence between the logical address and a physical address of the one memory block storing the data arrangement table, and stores the created table in the first table memory, externally acquires a logical address indicating the data arrangement table, specifies the physical address of the one memory block storing the data arrangement table based on the first address conversion table and the acquired logical address, in response to an externally-transmitted instruction, reads out the data arrangement table from the one memory block represented by the specified physical address, and externally sends the read data arrangement table, externally acquires a logical address indicating data to be read, and specifies a zone, to which a memory block represented by the logical address belongs, based on the acquired logical address, determines whether the second table memory stores a second address conversion table, which stores information representing a correspondence between the logical address and a physical address of the memory block belonging to the specified zone, and, when determined that the second table memory does not store the second address conversion table, creates the second address conversion table, and also stores the created table in the second table memory, and specifies, as a physical address indicating target data to be read, the physical address corresponding to the externally-acquired logical address, based on the second address conversion table, and reads out and outputs data stored in the memory block represented by the specified physical address.
According to this storage device, the first address conversion table, which stores the logical address of the memory block storing the data arrangement table, is kept stored in the first table memory regardless of which zone is specified. This eliminates the occurrence of the event where the stored address conversion table is updated every time the data arrangement table is accessed. Thus, lateness in the process of accessing data can be prevented.
The controller may: include an access history memory which stores the physical address, which indicates the target data to be read and which the controller itself has specified, and a logical address representing the physical address, in association with the physical address and the logical address, and specify a physical address indicating target data to be read, based on the physical address and the logical address which the access history memory stores.
According to this structure, even in the case where data including the data arrangement table is accessed, as long as accessing is preformed to the data stored in any block represented by the physical address and the logical address stored in the access history memory, there is no need to create the second address conversion table. Hence, the process of accessing data can be performed with high efficiency.
The controller may: include an empty block table memory which stores an empty block table storing information representing one or more empty blocks each of which comprises one memory block, select, of the one or more empty blocks represented by the information stored in the empty block table, a target empty block to store data, when data which is to be written and a logical address indicating the data are sent to the controller, and write the data to be written in the selected block.
The empty block tables may include: a first empty block table which stores information representing an empty block belonging to a zone including the memory block storing the data arrangement table; and a second empty block table which stores information representing one or more empty blocks belonging to one of the plurality of zones; and the controller may: determine whether the empty block memory stores the second empty block table, which stores information representing the one or more empty blocks belonging to one of the plurality of zones, and, when determined that the empty block memory does not store the second empty block table, creates the second empty block table which stores the information representing the empty blocks belonging to the specified zone,
Bataille Pierre-Michel
Kim Matthew
Tokyo Electron Device Limited
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