The decision on the File Allocation Table (FAT) patents reverses last October's preliminary rejection of the patents by the agency.
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."
The software giant was granted the first FAT patent in 1996 and in December 2003 announced that it and three 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. It speculated that, because the portfolio did not include licenses for use in free and open source software, Microsoft surely 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, including those using Linux, for the use of the FAT technology – hitting the community hard, because the use of any royalty-dependant software is prohibited under the GPL – the most popular licence for open source distributions.
In April 2004, PubPat filed a formal request with the US Patent and Trademark Office, asking it to revoke the patent. The lobby group submitted evidence of prior art – i.e. evidence showing that the feature being patented was already in the public domain. It enjoyed initial success: the USPTO issued preliminary rejections of the patents in September 2004 and October 2005.
However, the latter rejection was 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.
This difficulty now appears to have been resolved, with Microsoft announcing yesterday that the two patents had been declared valid.
Speaking to the Associated Press, PubPat Executive Director Dan Ravicher laid the blame for the rulings on USPTO procedures. He explained that challengers are unable to answer points raised by the defending party after they have made their challenge.
“I still believe that this patent is invalid,” he said.
Anti-software patent campaigner Florian Mueller also expressed concerns.
“This is now a situation in which Microsoft could cause major problems to Linux vendors and users. Microsoft may not want to do that yet for other considerations, but the USPTO's decision gives Microsoft the strategic option to do so at a time of its choosing,” he said.
The USPTO last week announced three initiatives to improve the quality and efficiency of the patent system. But Mueller was not persuaded that this would aid the situation.
“The example of the FAT patents shows that all those patent quality initiatives and patent pledges have no significant value to open-source developers, vendors and users if Microsoft ever wants to go for Linux's throat,” he added.
