In many cases, "free" isn't really free.

As an electrical engineer with an automotive background, when I think of Linux, I think of servers, PCs, supercomputers, and so forth. Embedded applications don't really come to mind when I consider Linux. However, Linux is used as an operating system for many phones, games, and other devices with embedded software.

Computer programs, often protected by copyright or trade secrets, can't be directly patented unless they're 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 (free), certain companies could have patents that could be infringed by people using Linux in embedded applications.

Linux is generally considered free software, but is its use in embedded devices protected by U.S. patents? 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 a nonlawyer to understand. Reviewing patent specifications and claims can give insight into the popularity and application of certain technologies throughout the years.

The claims are the most important part of a patent from a legal point of view because 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 as it's a complete technical description of the invention and usually has less of the legalese that's found in the claims. If a feature is found in the claims, it'll definitely be in the specification. However, a feature may be discussed in the specification but not in the claims.

Patent office databases
The United States Patent and Trademark Office (USPTO) makes a lot of patent information available online at www.uspto.gov/patft/index.html. You can actually look at patents dating back to 1790 (Abe Lincoln's patent #6,469 for "A Device for Buoying Vessels Over Shoals," on May 22, 1849, is in the online database!). Published patent applications can also be searched and viewed using the site. Patent applications are usually published on the site 18 months after they're filed. Batches of applications are published every Tuesday.

Patents are assigned to certain technical classes based on the nature of the invention. Each class has multiple subclasses that can be used to further specify the type of invention. You can see the patent classes at www.uspto. gov/go/classification/selectnumwithtitle.htm. As an example, patents related to operating systems might be contained in class 713, Electrical computers and digital processing systems: support; or class 719, Electrical computers and digital processing systems: interprogram communication or interprocess communication.

You can search for patents by looking in the appropriate classes and subclasses if you can determine them. However, embedded Linux applications could be located in many different classes because they can be classified by the end system's application.

Another way the databases can be searched is by keywords in the abstract, specification, or claims. The databases can also be searched by inventor, assignee, filing date, or several other parameters. You can combine the different search parameters logically using AND, OR, and the appropriate parentheses.