Contrary to popular opinion, Windows isn't the only operating system in which Microsoft is investing.

The Microsoft Research team has built from scratch a 300,000-line, microkernel-based operating system (OS) that has no roots in Windows.

That OS, code-named "Singularity," is slowly but steadily gaining visibility. The Microsoft Research team behind the project recently posted to the Web a 44-page technical research report about Singularity. Company officials discussed the project publicly at the June USENIX conference. And earlier this week, Microsoft's Singularity effort got some attention on Slashdot.

"What would a software platform look like if it was designed from scratch with the primary goal of dependability?" reads the opening of the Microsoft research report.

That was the question the Singularity team set out to answer two years ago.

"Singularity is not Windows. Every line of code was written from scratch," said Galen Hunt (search), a senior researcher with Microsoft Research who is helping to spearhead the Singularity project.

Hunt said Singularity is the largest cross-group project inside of Microsoft Research, involving about 35 researchers across the systems and networking, compiler, testing and other research teams.

Like all Microsoft Research projects, Singularity has no definitive commercialization trajectory. Microsoft could opt to commercialize it as is, embed elements of it in other products or simply rely on the learnings from the project to inform other efforts at the company.

Already, however, the Singularity work is generating ideas for the architectural team inside Microsoft's Core Operating System Division (COSD), and the Microsoft security team, Hunt said. COSD has been doing work to reduce dependencies among the different subsystems that comprise Windows. The security team has been wrestling with federated identity and distributed system challenges.

"We have an idea of how to minimize dependencies when writing an OS from scratch," Hunt said. "That's a technology transfer idea."

Singularity also could, hypothetically, act as the host operating system for something like Microsoft BigTop. BigTop is the code-name for a still-unannounced internal Microsoft distributed-systems infrastructure project.

Ultimately, all or parts of Singularity would most likely find a place in the embedded OS space, the server OS market, or both, Hunt said.

Singularity also is a proof of concept regarding the viability of managed code. Singularity is not the first OS written entirely in managed code, Hunt acknowledged. He bestowed that title on "Cedar," developed by Xerox PARC (search).

But the OS is currently written entirely in a combination of Microsoft's C# programming language, as well as a derivative of C#, which the team is calling "Sing#." (Sing# is a derivative of Spec#, which is a derivative of C#.) The ultimate goal is to write the OS entirely in Sing#, Hunt said.

While Singularity does rely on Microsoft's C#, it is not making use of Microsoft's Common Language Runtime (CLR) or the Java virtual machine. Instead, the team is relying on "Bartok," a Microsoft-Research-developed compiler and run-time environment.

"We have developed a working kernel, as originally conceived," said Hunt. "Now we can build a lot of components on top of it."

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