When is a version of Windows not Windows?

Mozilla and Google are complaining that Microsoft is going to bar versions of their browsers from running on the Desktop on Windows RT.

Microsoft isn't disputing this fact. The Windows brass have made it known for months that Microsoft planned to limit the Desktop in Windows RT -- the product formerly known as Windows on ARM (WOA) -- to run only Microsoft software, including four Microsoft Office apps, Internet Explorer 10 and a few other system components.

But what Microsoft is disputing here is rather odd. News.com is reporting that Microsoft Deputy General Counsel David Heiner told Mozilla that Windows RT "isn't Windows anymore" (according to Mozilla). Huh. Microsoft, you lost me there.

The name of the product in question is Windows RT. One might expect a product named Windows included at least enough of the Windows components to constitute it being named "Windows"-something. Windows Compact Embedded, Windows Embedded Standard, Windows Server, Windows Phone, Windows Embedded Automotive -- would Microsoft also claim these aren't "real" Windows? They aren't identical to Windows client, but they do share common components with it.

If you go back and read Windows Chief Steven Sinofsky's comments about Windows RT, he made it quite clear that while Windows RT was not identical to Windows 8, it includes quite a bit of shared Windows 8 code. In an interview with TechRadar in February of this year, he called Windows RT "a new member of the Windows family."

What is Windows these days? Is it just a brand? No. It's still an operating system. But it's an operating system has evolved considerably over the past 27 years since Windows 1.0 hit the market.

By the time Microsoft developers were building Windows Vista, Microsoft's own admitted that Windows had become a mess of code with too many interdependencies. That's what the "MinWin" project at Microsoft was all about: Untangling the Windows mess into a bunch of smaller pieces that could be recomposed for different environments..

The Softies seem to have moved beyond the MinWin name and mission, but they're still following the same general course. Microsoft teams building any kind of Windows operating system can pick and choose the pieces of Windows they need for different platforms. Some teams use more of the pieces than others. The coming Windows Phone 8 operating system, for example, is going to use a few of the "core" pieces of Windows -- the kernel, networking stack, security components and multimedia elements.

And what about Windows RT? It is another Windows SKU built using many of the elements of Windows Core. Windows RT does include various optimizations and removal of older/unnecessary features to reduce its install size on the smaller hard drives that are going to common on ARM devices, but it's still Windows.

I agree with my ZDNet colleague Ed Bott that the chances that Microsoft is suddenly going to allow Firefox or Chrome to run on the Desktop in Windows RT are close to zero. (And as Bott also notes, given Microsoft's tiny market share in tablets, it would be tough for either complaining party to find much of an antitrust leg to stand on here.)

Windows RT is more like Windows Embedded Compact, or even iOS on the iPad, than it's like Windows 8. It is optimized for performance and power and isn't designed to be replaced, dual booted,etc.  But the truth is, it's still Windows...