Microsoft describes the FAT file system as "the ubiquitous format used for interchange of media between computers, and, since the advent of inexpensive, removable flash memory, also between digital devices." In general terms it allows an operating system to locate and collate files stored on a computer disk or memory card.
The software giant was granted the patent in 1996 and in December 2003 announced that the main FAT patent (the ‘517 patent) and three other related patents were to be included in a new licensing portfolio.
But the Public Patent Foundation (PubPat), which lobbies against the current patent system, questioned the company's motives, speculating that the fact that the portfolio did not include licenses for use in free and open source software meant that Microsoft intended to use its patents to fight the competitive threat posed by free software.
Microsoft might, so the argument goes, be able to charge free and open source software developers for the use of the FAT technology – hitting the community hard because the use of any royalty dependant software is prohibited under the open source GPL licence.
In April last year PubPat filed a formal request with the US Patent and Trademark Office to revoke the patent. The lobby group submitted evidence of prior art – that the feature being patented was already in the public domain – and achieved some success when the USPTO issued a preliminary rejection of the patent in September 2004.
The re-examination process has now moved forward a step or two further with, in a decision released this week, the USPTO again rejecting the ‘517 patent and issuing a preliminary rejection for the related ‘352 patent.
However, the rulings were not based on the prior art claims. According to reports, the USPTO found the patents invalid only because of a technical discrepancy over who should have been listed as inventor.
Microsoft is planning to fight on.