The Bundespatentgericht (Federal Patent Court of Germany) has ruled that that Microsoft's European Union (EU) patent EP0618540 for its File Allocation Table (FAT) or "common name space for long and short filenames" is entirely invalid.

While Microsoft is expected to appeal this decision, it will be months before it appears in front of the next court. In the meantime, one of Microsoft main Android patent weapons has been rendered harmless for now in the EU.

This may sound like a minor patent. It's not. Microsoft has been using this patent since 2003 to pressure Linux and Android companies that use the popular FAT file system for compatibility with other operating systems.

Just how important is it? In July 2012, Microsoft got a German court to give them the right to ban all Motorola Android device sales in Germany because of it . Microsoft has also used this, and other FAT patents, to get numerous Android vendors to sign patent-licensing agreements.

These patent agreements, in turn, have made Android, not Windows RT, not Windows Phone 8, its most profitable mobile operating system. It's been estimated that Microsoft makes as much as $8 for every Android device sold. This would add up to Microsoft making as much as $3.4 billion in 2013 from Android sales . That's important.

Don't count Microsoft's FAT patent out yet. This patent has been attacked numerous times before. It has also been rejected and then reinstated at least once before.

Still, this latest result, combined with the recent judgment that the US version of this patent, "Common name space for long and short filenames," Patent No. 5,758,352 "invalid for obviousness," may finally blunt this patent's usefulness for Microsoft.

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