This works well for Microsoft. It even hosts Linux servers on the Microsoft Azure cloud service. Use Microsoft technologies to build your server solutions and you can take them between Linux and Windows. Great!
But Microsoft won't be open-sourcing the client-side .NET software, like WPF (Windows Presentation Foundation) and Windows Forms, which are used to build desktop applications with .NET. This would potentially allow businesses to migrate old .NET business applications away from the Windows desktop to other platforms. That's not beneficial to Microsoft's business model, so they're keeping those bits closed-source.
The free and open-source Mono 4.0 was recently released, and it includes some of Microsoft's newly open-sourced .NET code. That's a win, but Microsoft is ensuring the desktop bits stay locked up and Windows-only.
Microsoft still wants to sell and control Windows
But let's say Microsoft decides to change their tune and open-sources all of Windows 10 at some point. It won't happen, but let's pretend.
Microsoft would struggle with bigger problems. It'd still be able to sell Windows, but other people would be able to take the Windows source code, strip out the branding, and make their own freely downloadable variations of Windows. People could legally create versions of Windows without Windows activation built in, so they wouldn't need a product key. Microsoft wouldn't really be able to sell Windows--just support contracts that provided access to Windows patches quickly. And those patches could be taken and re-released for the community versions of Windows, just like how CentOS repackages the commercial Red Hat Enterprise Linux software.
And remember, Windows 10 isn't actually free--it's just a free upgrade for the first year for existing Windows 7 and 8 consumer users. It's not free for consumers after that, it's not free for DIY system builders, and it's not free for businesses. It's also not free for hardware manufacturers. Microsoft is still betting on Windows licensing revenue.
Worse yet for Microsoft, competing companies could take Windows and use it to make a competing operating system. Amazon's Fire OS is based on Android with Google's services stripped out and Amazon's included. Imagine a Fire OS version of Windows, one that ran all the Windows software you might want, but had Amazon's--or another companies--services integrated into it. This open-sourcing would actually hurt Microsoft's bid to become a services company.
Projects like Wine would also get a big boost, and it could become much easier to run Windows applications on non-Windows platforms.
The idea of Microsoft open-sourcing all of Windows is clearly a lot of hot air today, and even if it will happen someday, that day is far in the future. Really, Mark Russinovich's statement isn't about Windows. It's about Microsoft and its culture. He's saying that Microsoft is no longer ideologically opposed to open-source software, and they'll continue looking at open-sourcing things they can benefit from open-sourcing. Microsoft gets a good headline and gains some credibility points with geeks who like and use open-source software.
But all of Windows won't be open-source any time soon. Don't hold your breath!
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