Electrical computers and digital processing systems: memory – Storage accessing and control – Specific memory composition
Reexamination Certificate
2001-06-18
2003-07-08
Gossage, Glenn (Department: 2187)
Electrical computers and digital processing systems: memory
Storage accessing and control
Specific memory composition
C711S005000, C711S202000, C365S185110, C365S185290, C365S185330
Reexamination Certificate
active
06591330
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a system and method for handling data storage on a plurality of different types of flash devices and, in particular, to a system and method which manage the storage and retrieval of information on flash devices having different sizes of erasable units and/or read/write units, enabling them to behave as flash disks.
BACKGROUND OF THE INVENTION
Flash devices include electrically erasable and programmable read-only memories (EEPROMs) made of flash-type, floating-gate transistors and are non-volatile memories similar in functionality and performance to EPROM memories, with an additional functionality that allows an in-circuit, programmable, operation to erase portions of the memory. Flash devices have the advantage of being relatively inexpensive and requiring relatively little power as compared to traditional magnetic storage disks. However, in a flash device, it is not practical to rewrite a previously written area of the memory without a preceding erase of the area. This limitation of flash devices causes them to be incompatible with typical existing operating system programs, since data cannot be written to an area of memory within the flash device in which data has previously been written, unless the area is first erased.
Software products have been proposed in the background art to allow a flash device to be managed by existing computer operating programs without modification of the operating system program. However, these background art programs all have deficiencies. For example, one program operates the flash memory as a “write once read many” device. This background art software product cannot recycle previously written memory locations. When all locations are eventually written the memory cannot be further used without specific user intervention. To overcome these deficiencies of the background art, a flash File System (FFS) was disclosed in U.S. Pat. No. 5,404,485, which is owned in common with the present application and which is hereby incorporated by reference as if fully set forth herein. FFS provided a system of data storage and manipulation on flash devices which allowed these devices to emulate magnetic disks. As noted above, the relatively inexpensive cost and low power consumption of flash devices makes them a favorable choice for data storage, particularly for laptop, portable computers. FFS enhances the ability of flash devices to act as substitutes for magnetic disk storage. Indeed, FFS as disclosed in U.S. Pat. No. 5,404,485 has proven to be so useful that the data layout specification was adopted by the PCMCIA (Personal Computer Memory Card International Association) and JEIDA (Japan Electronic Industry Development Association) committees as a standard called Flash Translation Layer (FTL).
FFS essentially describes a virtual mapping system for flash EEPROM devices. The virtual map is a table which relates the physical address of a read/write block within the flash device to the virtual address of that block. Since each of these blocks is relatively small, 512 bytes, the size of the virtual map itself is quite large. FFS also includes a method of storing and maintaining the bulk of the virtual map on a flash EEPROM device, minimizing the amount of other memory required for storage of the virtual map.
As noted above, FFS has proven particularly successful for transforming flash devices into emulators of magnetic disk storage, so much so that it has been adopted as an industry standard. However, FFS cannot fulfill all of the requirements of the newer flash device technologies. In particular, FFS is not as successful with the NAND and AND flash technologies. Therefore, U.S. Pat. No. 5,937,425, which is owned in common with the present application and which is hereby incorporated by reference as if fully set forth herein, describes an additional implementation of the flash file system for these technologies. However, both of these implementations are useful mainly for specific types of technologies for flash memories.
For example, some new flash memory devices enable the operating software to select the exact size of the memory portion that is erased in a single erase operation. Traditional flash devices have a single size of an erase zone, which defined the chunk of data that could be erased in a single erase operation. This size was typically in the tens of kilobytes range. There are now flash devices which have more than one such erase zone size. For example, the SST34HF162X and SST34HF164X Concurrent SuperFlash devices from Silicon Storage Technology Inc. provide for erasing either 1 KWords sectors or 32 KWords blocks. Also, the NROM flash technology being developed by Saifun Semiconductors Ltd. also has this capability of being able to select the size of the erased portion from a group of two allowable sizes. This extra freedom of choice can be utilized for improving the background art methods.
SUMMARY OF THE INVENTION
The background art does not teach or suggest a mechanism for managing flash data on a plurality of different types of flash memory technologies. In addition, the background art does not teach or suggest such a mechanism which is highly flexible and which is able to operate more efficiently with these different types of technologies.
The present invention overcomes these deficiencies of the background art by providing a memory organization method which is suitable for different types of flash memory technologies.
Hereinafter, the term “physical unit” is defined as a unit on the physical media or hardware of the memory which is the smallest portion of the memory which can be erased or an integral multiple thereof. It is a portion of the memory which is contiguous, fixed in size and erasable. The term “physical block” is defined as being the portion of the memory for reading or writing data.
Hereinafter, the term “virtual unit” is defined as the same size as the physical unit.
Hereinafter, the term “virtual map” refers to a table which relates a virtual unit to at least one corresponding physical unit. As noted previously, each unit, virtual or physical, is composed of a plurality of blocks. The exact location of a block within a unit is determined according to one or more preset rules, as further described below.
Each physical unit is designated by a physical unit number. The location of each physical block is given by a physical block offset. Similarly, each virtual unit is designated by a virtual unit number. The location of each virtual block is given by a virtual block offset. It should be noted that each virtual unit number can correspond to one or more physical unit numbers. Thus, the mapping between virtual units and physical units can either be one-to-one or one-to-many.
Hereinafter, the term “writing data” describes the act of storing data on the flash memory. The term “reading data” describes the act of retrieving data from the flash memory. Hereinafter, the term “unwritten” indicates some portion of the memory, such as a physical block, which is capable of having data written to it. Thus, the term “unwritten” includes, but is not limited to, a portion of the memory which has just been erased.
In a computer or other electronic device having a flash memory organized according to the present invention, the operating system of that device interacts with the virtual units and virtual blocks for reading and writing data. The virtual media, which includes the virtual units and blocks, thus acts as an interface for the operating system to interact with the flash memory device. For example, the operating system issues a write command to write data to a virtual block at a virtual block offset. The virtual unit containing the virtual block is then located. The virtual map then locates a corresponding physical block within a physical unit of the memory, where the data are actually stored. Although the operating system issues read and write commands as though the virtual units and virtual blocks are the actual hardware of the flash memory, in reality the actual hardware is incorporated in
Friedman Mark M.
Gossage Glenn
M-Systems Flash Disk Pioneers Ltd.
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