If you want to use one of the FAT-based file systems (the MS-DOS and
VFAT (Windows 95) file systems), then you must say Y or M here
to include FAT support. You will then be able to mount partitions or
diskettes with FAT-based file systems and transparently access the
files on them, i.e. MSDOS files will look and behave just like all
other Unix files.

This FAT support is not a file system in itself, it only provides
the foundation for the other file systems. You will have to say Y or
M to at least one of "MSDOS fs support" or "VFAT fs support" in
order to make use of it.

Another way to read and write MSDOS floppies and hard drive
partitions from within Linux (but not transparently) is with the
mtools ("man mtools") program suite. You don't need to say Y here in
order to do that.

If you need to move large files on floppies between a DOS and a
Linux box, say Y here, mount the floppy under Linux with an MSDOS
file system and use GNU tar's M option. GNU tar is a program
available for Unix and DOS ("man tar" or "info tar").

The FAT support will enlarge your kernel by about 37 KB. If unsure,
say Y.

To compile this as a module, choose M here: the module will be called
fat. Note that if you compile the FAT support as a module, you
cannot compile any of the FAT-based file systems into the kernel
-- they will have to be modules as well.

source code:

fs/fat/