"The agency ruled that, based on existing inventions at the time, the ideas behind the FAT (File Allocation Table) patent would have been obvious and are therefore not subject to patent."

Oh dear, bad things on the horizon for Microsoft and their FAT patent, if they can't make a case within 90 days why their patent should be upheld. That's the word from the U.S. Patent Office, who have rejected a patent previously granted to Microsoft for the technology.

The re-examination of the Microsoft FAT patent came about because of concerns that Microsoft could use the patent to seek royalties from open-source software vendors. FAT is extensively used in all sorts of things, and pops up in open source all the time. The Linux kernel, for example, contains code for FAT read and write support, which can be compiled into the kernel or compiled as a module. Now, the Patent Office has confirmed Microsoft's FAT patent as invalid. Watch this space to see what happens when they appeal.