Source code is the set of underlying programming instructions that comprise an operating system.
In general, open source refers to software such as the Linux operating system that is allows programs to be modified by users. Microsoft has licensed elements of the Windows source code to less than 100 software and hardware developers working closely with Microsoft on evolving the operating system, according to estimates by sources close to Microsoft. The company also has licensed the Windows source to universities and government bodies under restrictive terms that allow them to work with the code, but not make changes to it. While Microsoft CEO Steve Ballmer has suggested over the past two years that the company was interested in making the Windows source code more freely available, there was little evidence that Microsoft actually was interested in doing so. Davis said that during the remedy phase of the Department of Justice's antitrust trial against the software giant, Microsoft fought suggestions that it be required to share Windows source code with any kind of neutral third-party licensing body.