Microsoft's contentious patent describing the mechanism used to store long filenames on FAT filesystems without breaking compatibility with old applications has been upheld by the German appeal court after a prior court decision ruled it invalid. This mirrors a 2006 decision by the USPTO concerning the equivalent US patent.

The German Federal Patent Tribunal claimed that the patent EP0618540 lacked the element of invention in 2007. The Tribunal stated that the work done on the Rock Ridge Interchange Protocol, which allows long file names to be used on the ISO9660 filesystem used on CDs, solved the same problem, and since Rock Ridge was developed in 1991, it predates the FAT long file name work.

The appeals court rejected this reasoning due to technical differences between the two systems, stating that Microsoft had to solve new problems that the Rock Ridge work didn't address. In particular, the way long names on FAT were designed so that legacy systems would ignore the new names was deemed to be significant.

The FAT long-file-name patents are of particular importance to Microsoft, as it seeks to obtain license fees from companies wishing to use the FAT and FAT32 filesystems, which are an integral part of many embedded devices such as cameras and cellphones. If these patents weren't upheld, Microsoft's ability to demand such license fees would be greatly curtailed.

This point was made clear last year, when Microsoft filed suit against navigation device maker TomTom, claiming that its products violated the US patent. TomTom countersued, and the two companies soon settled. This case, and subsequent settlement, may have repercussions to the Linux community. Some of the TomTom devices that Microsoft named used Linux, implying that Linux's FAT support violates the Microsoft patents.

The German decision also shows that European courts are willing to grant software patents, provided that those patents represent genuine technical innovations (like encoding long file names on a filesystem that can't store them) and aren't just business processes (such as running auctions on the Internet).