FAT as it is known today made its debut in 1980 with the first version of QDOS, the ancestor of Microsoft's PC-DOS and MS-DOS.

FAT licensing

Although technical details of the FAT file system derive from CP/M and have been widely known and widely disseminated in the PC community for many years, and although the file system itself is widely considered to be obsolete, it should be noted that in 2003 Microsoft made a point of asserting intellectual property claims to the system. Citing patents, Microsoft claimed that licensing fees are required for its use in such applications as removable solid state media, and consumer devices using such media.

This claim by Microsoft is controversial, for a number of reasons. Microsoft itself has admitted that it developed its first FAT file system in 1976, so no patents could apply to an implementation of the original version. Copyright law could not prevent a re-implementation of FAT either.

Microsoft has cited 4 patents, dating from 1995 on, for FAT. All of these patents relate to storing both long and short filenames in a single file system. A Slashdot discussion on December 4, 2003, analyzed these patents and participants (particularly Svartalf) reported the following:

* Patent 5,579,517 - Common name space for long and short filenames. Filed for on April 24, 1995. This appears to only impact someone using a Common Name Space for long and short filenames. This is the scheme Microsoft deployed for "Chicago" (the codename of Windows 95 while in development). This patent is likely to be invalidated (if challenged) by Microsoft's prior art release of Chicago to the world in December 1993.

* Patent 5,745,902 - Method and system for accessing a file using file names having different file name formats. Filed for on July 6, 1992. This patents allowing renaming of just the name and preserving the extension for the purposes of keeping track of the filetype. It is unclear that other implementors would need to implement this patent to implement a FAT system.

* Patent 5,758,352 - Common name space for long and short filenames. Filed on September 5, 1996. This is extremely similar to the 5,579,517 Patent; see those comments.

* Patent 6,286,013 - Method and system for providing a common name space for long and short file names in an operating system. Filed on January 28, 1997. This is a detailed description of how Windows 95/98/Me handles long filenames on an x86-32 platform. It is unclear this patent would apply to anything other than an exact clone of Windows 95/98/Me. This patent is likely to be invalidated (if challenged) by Microsoft's prior art release of Windows 95, two years before the filing date,

In addition, there also seems to be prior art for at least the first, third, and fourth patents in the Rock Ridge Interchange Protocol standard for UNIX, which was an IEEE draft specification on at least July 13th, 1993. This protocol defined a method to support long and short names on the same media (as well as additional information) to support Unix systems.

And of course, there is the simple question if this is really an innovative idea at all. Patents are supposed to be granted for new ideas; the notion of not removing short names, but adding long name information as well, is an option that is immediately obvious to any practitioner in the field.

In short, many have concluded that these patents only cover implementations that include support for long filenames, so it likely that removable solid state media and consumer devices only using short names would be unaffected. Also, there is good reason to believe the patents would be found invalid or unnecessary if challenged. In particular, many or all such patents are believed by many to be invalid because of previous public release, prior art, or because the technique would be obvious to a practitioner.