Flash
Memory: Theory and Applications
Flash
file systems
Because of the particular
characteristics of flash memory, it is best used with specifically designed file
systems which spread writes over the media and deal with the long erase times of
NOR flash blocks. The basic concept behind flash file systems is: When the flash
store is to be updated, the file system will write a new copy of the changed
data over to a fresh block, remap the file pointers, then erase the old block
later when it has time.
One of the earliest flash file
systems was Microsoft's FFS2 (presumably preceded by FFS1), for use with MS-DOS
in the early 1990s. Around 1994, the PCMCIA industry group approved the FTL
(Flash Translation Layer) specification, which allowed a flash device to look
like a FAT disk, but still have effective wear levelling. Other commercial
systems such as FlashFX by Datalight were created to avoid patent concerns with
FTL.
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