A prior art method of file management designed specifically for flash memory is explained in U.S. Pat. No. 5,404,485 issued to Ban. Ban, however, still takes the more conventional and disadvantageous approach of manipulating data stored in flash memory by first reading the data out to a large RAM, manipulating the data in RAM, erasing the flash memory where the data was originally stored, and then writing the data from RAM back to a contiguous block of flash memory. Ban also disadvantageously creates a file structure similar to DOS which maps the location of stored data.
The method of Ban creates several severe overhead burdens on the system which substantially hurt system performance. More specifically, Ban uses a virtual memory mapping system similar to the DOS FAT, the virtual memory map converting virtual addresses to physical addresses. Using this method of indirection, Ban attempts to facilitate use of flash memory as RAM. The problem with this approach is that Ban creates the need for this indirection because data manipulation takes place outside of flash memory. Ban mistakenly teaches that the time wasted copying blocks of data from flash memory to RAM for manipulation then back into flash memory is unavoidable.
A further significant drawback to Ban is the lack of fault tolerance in a system that utilizes a virtual map stored partially in RAM. The system is inherently unstable because any loss of power to RAM destroys the map which must then be reconstructed before the system can read or write data to flash memory.
Another drawback of Ban is that the RAM requirement grows as flash memory grows. This is the consequence of using a virtual map whose size is dependent upon the total amount of RAM available, and is thus a ratio of the larger flash memory media in order to reflect a scaled version of what is stored in physical addresses.
Ban essentially teaches that it is necessary to follow the method already used in the conventional DOS operating system which also relies on long-term storage in conjunction with significant RAM resources. That is to say, the access to and structure of storage media is changed as little as possible so that the operating system does not have to be significantly altered to utilize flash memory.
While the objective of making a system see flash memory as RAM with its accompanying benefits of non-volatility is desirable, the approach taken by Ban fails to take full advantage of flash memory by continuing to rely heavily on RAM resources. This system then suffers from lack of fault tolerance which not only jeopardizes reliability, but slows down the entire system by requiring large data transfers between RAM and flash memory.
Accordingly, the challenge is to use a non-volatile, long-term storage medium such as flash memory which can take advantage of increased fault tolerance to power interruption, significantly reduced RAM resources, and reduced system overhead caused by data transfers between RAM and the storage medium, while overcoming the erasure drawbacks unique to flash memory.
