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."