FAT

FAT (or File Allocation Table) is a file system developed in the late 1970′s and first used in 1980.  There have been four versions since its inception (FAT12, FAT16, FAT32 and FAT64) and it supported by nearly all modern operating systems.  The number after each version refers to the total number of clusters (that is 2^NUMBER) the file system can support.

Limitations

One major limitation of FAT is that it does not support permissions for the files it stores.  Also, the it have very limited time stamp support.

References

There are many resources on the Internet which provide a wealth of information about FAT.  One such overview is found in the Wikipedia article on FAT.