Although the names Windows 8.1 and Surface 2 suggest refinements of previous products, Microsoft is also using this seemingly evolutionary release phase to push forward with a controversial plan to redefine Windows, its core product. In the firm's new view of the decades-old product line, Windows isn't what it used to be.

In some ways, the change started with the original release of Windows 8 last year, when Microsoft added a new touch-first mobile environment (which many still call Metro) to the classic Windows desktop. At the time, Microsoft refused to name new Metro bits in Windows, and multiple executives told me that "it was just Windows." But the dichotomy between Metro and the desktop caused many users fits. It might have just been Windows in name, but it was really two separate things tied together: Metro and the desktop.

Related: "Microsoft Releases Second-Generation Surface Devices"

A year ago, Microsoft was also differentiating between different Windows versions explicitly. Windows RT was the ARM-based version of Windows 8, and Surface with Windows RT (Surface RT, for short) was the device it made that ran this OS. Surface Pro, which utilized Intel chipsets and ran the mainstream Windows 8 Pro software, was its more traditional laptop-like offering. And Windows Phone was, of course, a completely different thing.

Today, Microsoft is marketing its new line of Surface products differently. And the RT brand is out: Surface 2 runs Windows RT 8.1, but you have to really hunt to discover that. And although Microsoft is still selling the year-old Surface RT as an entry-level product, it has removed RT from that product's name too: Now it's just called Surface.

On the software front, Microsoft is pushing to combine Windows RT and Windows Phone, and though the resulting product's makeup and branding are currently unknown, it's likely that the RT and Phone bits will fall by the wayside as Microsoft pushes what I call a "One Windows" agenda: One version of Windows that runs the same apps, works with the same hardware drivers, and offers a consistent set of experiences. You can see this Windows today in the "Metro" half of Windows 8.1/Windows RT 8.1. That environment, not the desktop, is what Microsoft sees as the future of Windows.

This change will further impact the traditional Intel-based versions of Windows, in that they will remain a superset of "Windows"—the RT/Phone version—but one that can still run legacy Windows desktop applications, too, and work on increasingly rare traditional desktop PCs and workstations. This change is already happening: With Windows RT 8.1, Microsoft has removed the desktop tile from the Start screen. I expect the desktop to be further deemphasized, if not completely removed, from future (non-Pro) versions of Windows.

Within a few years, mainstream versions of Windows will be known for their flat, Metro-style and touch-first UIs, and the legacy Windows desktop will be available only via increasingly archaic and uncommon desktop PCs. This new Windows will run on a common core, as it does now, and scale across multiple device types, including phones, tablets, PCs, living room set-top boxes, kiosks, automobile systems, and more. It will be more secure, smaller, and less complex. And it will just be Windows.

If you find this strategy to be confounding, you'll further enjoy a plan to rebrand Microsoft's on-premises server lineup as Azure, the name currently used for the firm's cloud computing infrastructure. (This one isn't settled, last I heard, although the push for a non-Windows brand could gain momentum if Server & Tools chief Satya Nadella becomes the new Microsoft CEO.) As we move forward, these in-house servers will be as uncommon as traditional PCs, in the view of some at Microsoft, and will serve only to bridge the past with the cloud computing norm.

All of this is still in flux, of course. But make no mistake: The trends that are sweeping the industry are impacting Microsoft in multiple ways, and they are impacting Windows as well.

Related: "Microsoft's Move to Devices and Services"