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What, actually, is at stake here? Microsoft has long claimed that Linux violates more than 200 of its patents, but the company has never provided any information with regard to what those patents are--until, it would appear, now. As noted, the Redmond company is suing TomTom and its GPS auto-navigation software with regard to a number of patents--eight in all. TomTom makes use of the Linux kernal in its products. But the kicker, according to ComputerWorld, as far as Linux is concerned appears to be patent number 5,579,517.

More specifically, we read from the patent abstract: "An operating system provides a common name space for both long filenames and short filenames. In this common namespace, a long filename and a short filename are provided for each file. Each file has a short filename directory entry and may have at least one long filename directory entry associated with it. The number of long filename directory entries that are associated with a file depends on the number of characters in the long filename of the file. The long filename directory entries are configured to minimize compatibility problems with existing installed program bases."

For those with a taste for history, this will be read as the "VFAT" innovation (or kludge, depending on your point of view). Prior to Windows 95, versions of Windows relied on FAT file system. This system provided for filenames that were a total of eleven characters along, excluding the dot. Examples? WINWORD.EXE or MYFILE01.DOC.

Wishing to outdo other current operating systems for filename length (Mac System 7's Finder had a technical limit of 31 characters for each file name), Microsoft developed VFAT, which allowed filenames up to 255 characters long.

However, Windows 95 had to deal with the fact that many people would be using it with programs developed for earlier versions of Windows (and DOS)--programs that would only save filenames in the 8.3 format. In order to get around this issue and allow Windows 95 to work well with earlier versions of Windows, Microsoft's VFAT had to recognise filenames written in both systems. It did so by creating a single "name space" for a given file's 8.3 version and its 255-limit version. The company received a US patent for this feature on 26 November 1996.

Now, the differences between "patents" and "copyrights" are many. It is highly unlikely that Linux infringes on any idea of copyright for VFAT (the code in Linux that allows for the reading of and writing to VFAT is not the same code as that which Microsoft's products use). However, the very fact that Linux has this capability could be taken as a violation of Microsoft's patent.

Think about the following: I can write a sentence that describes how to tie one's shoelaces. Perhaps I would write, "Cross both laces over and run one under the other... [etc]." You too could write a sentence describing how one ties one's laces: "Take one lace in the left hand and the other in the right... [etc]." Now, the second description would be different enough not to affect my copyright on the first sentence. However, if I owned a patent on tying one's laces, then you would have violated my patent by even trying to describe, albeit in a different manner, the process of tying laces.

This difference is at the heart of many debates over the whole issue of software "patents". So far, only a few countries even allow software patents (the US being one of them). This key reason that many object to software being patentable is glaringly present here. Think about murder mysteries. Agatha Christie took her fame from providing highly formulaic popular fiction organised around simple plots involving the solution of murders (by, among others, a presumably virginal spinster and an asexual Belgian). She owned (and now her estate owns) the copyright to those works. However, many others since (and likely before... "prior art"!) have written murder mysteries structured similarly to hers. If she had held a patent to the "murder mystery" genre, then no one else could have legally written murder mysteries.

Getting back to Microsoft's lawsuit against TomTom and (by proxy) Linux, we see that they are actually asserting their patent to the VFAT file system. They are not challenging the fact that Linux can read from and write to VFAT by a different means from Microsoft's. They are claiming the patent right, duly granted by the US PTO (Patent and Trademark Office), to stop anyone doing that, whatever the code used. This is not a patent they have spent much time asserting--companies who churn out memory devices routinely use file-system technology that "breaks" the Microsoft patent, but Microsoft have thus far been hesitant about asserting their legal rights there.

The Public Patent Foundation tried to have Microsoft's patent revoked on the grounds that it was obvious (and that there was "prior art"). The patent was revoked in 2004, but then, after Microsoft submitted a revision of the patent, it was reinstated. The irony here is that there are perfectly good open-source file systems out there that are free and technologically superior to any FAT-based solution. But companies over the years have defaulted to it because of the monopoly Microsoft has with Windows... and Microsoft has known this and, it would not be a stretch to claim, welcomed this, for it keeps them in the driving seat. The PTO's reinstatement of Microsoft's claim, even in light of the fact that the US government declared Microsoft to be a monopoly (which means that they must obey special rules limiting their "abuse" of their monopoly status that other businesses do not have to obey), is what will no doubt be probed in the trial.

It remains to be seen what will happen with this lawsuit. The issue is even more complicated than I've explained it here: for instance, it appears to involve the use by Microsoft and other companies of secret cross-licensing agreements which "break" the GPL. It could, however, be bad news for Linux (at least in America), or the patent claim which directly affects Linux could be revoked a second time. At the end of the day, this is a bold move by Microsoft in its always-uneasy relations with Linux and the open-source world.