Many of the links you find on the web regarding source code for FAT file systems are rather limited. Even some of the links suggested earlier in this thread are limited. Some of the limitations you will see are..."only reads files"..."does not follow cluster chains"..."does not support sub-directories"..."no long filename support"....etc etc.

Here is a link to a complete FAT file system package at the open(), read(), write(), close() level of file access. It is still necessary to provide the low level block acess to your IDE / PCMCIA / COMPACT FLASH device. But that code is really seeming to be the "easy" part.

FAT File System Code

Hope this helps.
Michael Karas