Last week, Microsoft (NSDQ: MSFT) sued TomTom for infringing on patents relating to (among other things) the format of its File Allocation Table 32-bit (FAT32) disk format. These patents relate to mundane issues like how to translate pretty names like "C:\Temporary Files" into ugly short ones like "C:\TEMPOR~1" that older programs can understand, and the layout of files on the physical media such as hard drives or flash memory.
So what are the implications of Microsoft having a patent on FAT technology? Let's look at a simple example. Whenever you plug a flash drive into your PC, the odds are that it's formatted with Microsoft's FAT32 technology. If you take that flash drive to another non-PC device, the software on that device needs to be able to understand the FAT32 format in order to read the files. Microsoft says that to do that, you need to license their patents.