There’s been an interesting debate lately about whether Microsoft’s ARM-based derivative of Windows 8, called Windows RT, is really Windows. This debate arose out of a recent news story, in which Mozilla and Google have both complained about Microsoft’s decision to prevent them from making a desktop-based web browser for Windows RT. More recently, a US Senate subcommittee has decided to investigate this complaint, which could of course have antitrust implications.

This latter fact alone means that the debate about whether Windows RT is really Windows isn’t just the typical blogosphere noise. Infoworld’s Woody Leonard notes in his own coverage of this event that Windows is really just a brand, and nothing more, and that Microsoft certainly has the right to call any product “Windows” if it wants. Fair enough, but I’d take that a bit farther.

For starters, Microsoft has been doing this kind of thing for decades.

In the early 1990s, when Dave Cutler and other refugees from Digital Equipment Corporation were busy building a product they called NT, their only real goal was to create a modern operating system that was resilient, secure, and sure to beat anything DEC was bringing to market. But Microsoft of course branded NT as Windows NT, threw the Windows 3.x user interface on top, and spent the next decade foisting multiple and somewhat incompatible products on the product, each of which was called “Windows.”

(If you’re interested in this stuff, be sure to read G. Pascal Zachary’s now-legendary book Showstopper: The Breakneck Race to Create Windows NT and the Next Generation at Microsoft, which has been reissued in new Kindle, Nook, and paperback formats.)

The DOS/Windows 9x and NT product lines eventually merged in Windows XP, of course, but that was just the tip of the “everything is called Windows” strategy that Microsoft has employed ever since. There was Windows CE, which again looked like Windows but was designed to be a very modular OS for handheld PCs and “palm-sized PCs” in the early days but has expanded fairly dramatically since. Windows CE, of course, begat PocketPC, which became, yes, Windows Mobile and then, more recently, Windows Phone. None of these products are architecturally related to mainstream desktop and server versions of Windows.

But at least they’re OSs. Microsoft has used the Windows name on every kind of software imaginable -- Windows Mail, Windows Calendar, Windows Media Center and many, many more -- and on services, too, including Windows Live and Windows Azure. On and on it goes.

(I’m surprised the Xbox escaped this branding, but the failure of other unique brands such as Zune suggests that the Xbox might end up being the exception to the rule.)

And then we come to Windows 8 and Windows RT. As I noted back in February in "With WOA, It's NT All Over Again," one of the neat things about Windows RT is that it allows Microsoft to much more aggressively remove non-core technologies from the product, shedding legacy deadwood at a pace that isn't possible with traditional Windows versions that existing users must be able to upgrade to. Windows RT (previously called WOA, for Windows on ARM), is unencumbered by this need.

It might also be functionally less compelling. As I’ve also noted before, although Windows RT will look and feel just like the core version of Windows 8, there’s a sharp and none-too-obvious difference between the two. That is, where Windows 8, like previous Windows versions, targets a wide range of Intel-compatible hardware and will run all older Windows software, Windows RT targets a new and unproven family of sealed ARM-based devices and won't run older Windows (desktop-based) software.

(Side-note: Developers who have seen early Windows RT prototypes tell me that the performance isn’t great at the moment and that, as expected, the system supports only a minimal amount of the technologies found in x86/x64-based versions of Windows.)

The inability to write desktop software that runs on ARM is, by the way, at the center of the Mozilla and Google complaint. You see, Microsoft is providing a desktop version of Internet Explorer on Windows RT. But it won't let Mozilla, Google, or any other company develop desktop-based web browsers (or any other desktop software) on Windows RT. The system is as sealed as the hardware on which it runs, and only new, Metro-style WinRT apps are allowed.

For this reason, I believe that only Windows 8-based systems should be considered PCs whereas Windows RT-based systems are devices, like the iPad or a smartphone, and not PCs. This notion is furthered by the fact that Windows RT devices can't join a domain or be managed with Group Policy. You know, like real PCs.
But there are two things that are really interesting about this argument, I think.

First, users have expectations about what Windows is and does. And although previous Windows-like products did look and work much like Windows, they were clearly not Windows. This time, it’s very subtle, and consumers, especially, are going to be confused when the Windows device they buy won’t run some favorite desktop application or utility. Calling it Windows RT isn’t going to help.

Second, it’s worth remembering that if Windows RT takes off and is truly successful, it becomes Windows. That is, it does what NT did decades ago, existing for a time side-by-side with what used to be Windows and then eventually supplanting the old Windows.

And that’s when things get weird, isn’t it? Today, Windows RT isn't Windows. But it might be . . . eventually. And that’s a future that we should all be ready for.