Over the last few years, Microsoft's chief executive Steve Ballmer has made a number of highly contentious claims that Linux uses "our" - meaning Microsoft's - "intellectual property", and infringes as many as 235 Microsoft patents.

Last week it was revealed that Microsoft had filed an action for patent infringement against TomTom, the Dutch manufacturer of Linux-based GPS navigation systems, and many have seen this move as the opening skirmish in a coming patent war.

Although the action isn't against Linux, it is implicated in two of the eight patents for which the claim is made. These two US patents, #5,579,517 and #5,758,352, bear the titles "Common name space for long and short filenames", and are specific to the Microsoft FAT (File Allocation Table) file system.

FAT claims

FAT was the file system for DOS and Windows 9x and became the standard file format for digital devices. Nobody would pretend that FAT represents any great technical accomplishment or innovation. FAT is used for digital devices and SD cards because it provides interoperability with Windows, and interoperability with Windows has been essential to the manufacturers of such devices because Microsoft has owned the desktop.

FAT is also used by Samba which is used by most Linux and Unix distributions to provide full file client and server interoperability with Windows networks. A Linux utility dosfstools is used by TomTom to transfer files between SD cards and Linux-based GPS navigation systems.