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There are a lot of different people that contribute code to the Linux kernel. In fact, according to the 2012 Linux Kernel Development report from the Linux Foundation, more than 7,800 developers from nearly 800 different companies have participated in Linux kernel development.

Not all of those companies and developers participate in every kernel release. According to the report, for the recent Linux 3.2 kernel release, some 1,316 developers contributed, representing 226 different companies. While there is lots of participation, over the last five years the top 30 developers have contributed 20 percent of the total code.

When it comes to companies that sponsor kernel developers, the top company affiliation is Red Hat, which has contributed 11.9 percent of kernel code. Novell follows at 6.4 percent, Intel at 6.2 percent and IBM at 6.1 percent. Supposed "Linux nemesis" Microsoft cracks the list this year as well with 1.0 percent kernel code contribution. Surprisingly Ubuntu and its corporate sponsor Canonical are not in the report's list of the top Linux kernel development firms.

"Of course, some might believe that Microsoft's position is a surprise; though, we've been aware of their work and motivations for some time now," Amanda McPherson, VP of marketing and developer services at the Linux Foundation told InternetNews.com.

Microsoft's contributions, however, are not about helping to advance Linux but are more about enabling support for their own technologies, as well as ensuring legal compliance. Linux kernel developer Greg Kroah-Hartman confirmed to InternetNews.com that Microsoft's Linux contributions are all Hyper-V related items.

Since the Linux kernel is licensed under the GPL open source license, for Microsoft to get its virtualization technology properly supported by Linux the company was legally required by the license to contribute code. According to Kroah-Hartman, Microsoft has also been properly maintaining their code in the mainline Linux kernel as well.

While there are a lot of known entities contributing to Linux, there are lots of developers that don't have a company affiliation. Since the 2.6.36 kernel, 16.2 percent of kernel changes were contributed by developers with no corporate affiliation. An additional 4.3 percent of changes were contributed by developers with an 'unknown' affiliation and 2.6 percent of changes were contributed by consultants.

"Consultants say that they are consultants," Kroah-Hartman explained. "Unknown, means we don't know who they work for, or, in a few rare cases, they don't wish to say who they work for."

The unknown category is one that has shown up in all previous Linux development reports as well. Back in 2008, the Linux Foundation reported that the number of unknown corporate affiliations came in at 12.9 percent.

"The category doesn't change, it still consists of people who we don't know whom they work for," Kroach-Harman said. "Almost all of these are very few individual contributions; it's just a large number of individuals that fall into this category."

Sean Michael Kerner is a senior editor at InternetNews.com, the news service of the IT Business Edge Network, the network for technology professionals Follow him on Twitter @TechJournalist.