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Computer programs, though often protected by copyright or trade secrets, cannot be directly patented unless they are used for something tangible, such as signal processing or hardware control. For example, an operating system could be patented as a business method or a method to control computer hardware. Even though Linux is open source, freeware, companies could hold patents that could be infringed by people using Linux in certain applications.

A patent consists of several parts, including the abstract, specification, and claims. The abstract is a concise summary of the specification, while the specification is a complete description of the invention. The claims are where the majority of the legalese is found and are generally difficult for non-lawyers to read.

The claims are the most important part of a patent from a legal point of view, since they define exactly what part or aspect of the invention is patented and, therefore, legally protected. From a technical point of view, the specification is often the most useful, since it is a complete technical description of the invention and, usually, has less of the legalese that is found in the claims. If a feature is found in the claims, then it will definitely be found in the specification. However, a feature may be discussed in the specification but not in the claims.

Searching methodology and notes

Searching the titles of patents can often uncover inventions that are closely related to a certain technology, although some inventors use titles (and claim language for that matter) that do not clearly indicate to what an invention pertains. For example, an inventor might use "Graphite Communication Instrument" as a title for a pencil. Still, it is often useful to search the title, abstract, claims, and the specification of patents for the item of interest.

To keep things simple, I searched issued US patents and pending patents (publications) for the term "Linux" in the title, abstract, claims, and the specification. In other words, I did not search for GNU, Red Hat, open source, free operating system, or other terms. I just searched for patents and publications that directly mention Linux. This simple search gives a general idea of what is happening related to Linux in the US patent arena.

Note that inventions that are listed in the issued patents database may also be listed in the publications database. This is because patent applications are left in the publication database even after a patent is issued, so there is some duplication between the two databases. Also, patent applications are not published until 18 months after the filing date (if they were filed on or after 11-29-2000), so many from 2006 and 2007 do not show up in the publication database yet. I performed all of the following searches on October 22.

Searching patents and patent publications for Linux

Searching the issued US patent database titles for "Linux" resulted in three hits, covering migrating from Linux to Windows (Centaris Corporation -- issued 2007), viewing Windows files on a Linux system (Gateway, Inc. -- issued 2007), and online diagnostics on Linux (IBM -- issued 2004). Searching the pending US patent publication database titles for "Linux" resulted in 16 hits related to inventions covering things such as diagnosing operating system resources supporting USB device driver development in Linux system (Electronics and Telecommunications Research Institute, Korea - filed 2006), electronic devices with embedded Linux (Moxa Technologies, Taiwan -- filed 2005), and a mobile handset based on Linux with compression and decompression techniques (Bitfone Corporation, California - filed 2005).

Searching the issued US patent database abstracts for "Linux" resulted in 17 hits related to inventions concerning topics such as transferring resources between different operation systems (assignee not available - filed 2001), remote and automatically initiated data loading and data acquisition of airborne computers (assignee not available - filed 2002), and apparatus for remote installation of an operating system over a network connection (Akamai Technologies, Massachusetts -- filed 2002). Searching the pending US patent publication database abstracts for "Linux" resulted in 75 hits related to such things as a Web browser operating system (National Science foundation -- filed 2005), smoke alarm (assignee not available - filed 2003), and a method of implementing a Linux-based embedded system for mobile communication (Pantech Company, LTD, Korea - filed 2004).

Searching the issued US patent database claims for "Linux" resulted in 76 hits. Searching the pending US patent publication database claims for "Linux" resulted in 373 hits. Many of these patents and publications have claims that are dependent type claims that state something like "the device, method, or system of claim x where the operating system is Linux." One example is patent publication 20040221275 (Computer Associates Think, Inc.) which has independent claims directed to a method and apparatus for adapting for a kernel on a target system and also has dependent claims stating that the kernel is a Linux kernel.

Searching the issued US patent database specifications for "Linux" resulted in 4,697 hits with filing dates back as far as 1995. Searching the pending US patent publication database specifications for "Linux" resulted in 16,694 hits. Figure 1 shows the number of patents and publications per filing year that mention Linux in the specification. Note how the number of issued patents peaked in 2001, while the number of applications seems to be steadily increasing each year. Remember that 2006 and 2007 are partial years in that not all of the applications from those years have been published. These conflicting trends are likely due to many of the applications, from filing year 2002 and forward, still being in a pending status (waiting to be approved and issued as a patent or finally rejected). Given enough time for the applications to be completely examined, the issued patents will likely show the same upward trend for the same filing years.

While the statistics are interesting, the bottom line is that it would be wise to search the US patent database before commercially using the operating system in a particular application or adapting the Linux kernel for a particular application.

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