The contents of flash memory are updated following a preceding sector erase of the relevant area. Conventional storage mediums do not generally require such erasures. Accordingly, there is a findamental incompatibility in the use of flash memory as a data storage medium with computer systems using conventional operating systems.
One method for storing data on flash memory is disclosed in U.S. Pat. No. 5,404,485 entitled “Flash File System”, issued to Ban. In this case, a virtual mapping system is provided that allows data to be continuously written to unwritten physical address locations. The method used by Suzuki (US 2002/0166022 A1) also uses logical to physical address mappings. When virtual or logical memory maps are used, the use of standard file-system utilities to debug/repair the stored file-system is precluded when the file-system data is uploaded from an embedded device that uses flash memory and is moved to a customer support site. The method described as part of Ogawa (U.S. Pat. No. 5,933,847) uses the Least Recently Used (LRU) algorithm to select cached sectors that can be freed. This will not be optimal in many cases when flash memory emulates a disk drive in an embedded device. Also, these techniques do not automatically detect critical meta-data sectors and offer them persistent storage or preferential treatment.
In view of the above, a need exists for a manner of managing data in flash memory that addresses certain limitations of prior art.
USPTO Backgrounds
USPTO Backgrounds