On the eve of Windows 8’s launch, it’s clear to me that many people still don’t really understand what’s happening here. So I’d like to reiterate a few points I’ve been making for a while now that don’t seem to have sunk in yet.

New Windows Runtime & Apps Platform

First, Windows 8 is a new mobile operating system and not an evolution of the previous Windows codebase. Yes, an evolution of that previous codebase is present, complete with an improved desktop environment. But the big news in Windows 8 is the Metro environment, a new runtime engine called Windows Runtime, and a new apps platform. This is the future of Windows, not the desktop.

(It doesn’t help that Microsoft says it expects Metro and the desktop to co-exist for some time to come. Hey, WINS and DNS “co-exist” in Windows Server today. That doesn’t mean they’re equals.)

Completely New Mobile Platform

Second, that Metro environment -- I know, I know, Microsoft doesn’t like that word anymore -- is much more than just another runtime like .NET or Silverlight. No, it’s nothing less than a completely new mobile platform based on Microsoft’s learnings from Windows Phone, of course, but also competing mobile platforms such as Android and iOS. (I like to think of Metro as a platform that improves on the competition in key ways, much like PowerShell improved on its UNIX shell inspirations.)

Mobile Apps Not "Applications"

Third, the programs that run in Metro are mobile apps, or just apps. They aren’t “applications,” as we should rightfully call the desktop applications of old.

Please let those points sink in for just a moment, because understanding these changes is key to understanding Windows 8.  

And not just Windows 8, but also Windows RT, the ARM-based version of Windows 8. Windows RT is today’s NT, or today’s 64-bit versions of Windows, in that it represents the future. The first RT implementation might or might not see the widespread adoption of future versions, but no matter: The guts of RT -- Metro -- is the future. And in some ways, Windows RT is a purer implementation of Metro, because it dispenses with huge chunks of legacy desktop goo.

Yes, I know, I’ve written around these topics before. And I’ll probably need to do so in the future, too, based on the confusion I’ve seen at shows, via email, on Twitter, and elsewhere.

But these distinctions -- new mobile OS versus next version of Windows 7, apps versus applications, and so on -- is important. By engineering Windows 8 this way, and not just making a separate Metro-only OS for tablets and devices, Microsoft is sending us an implicit but, I think, clear message -- which is that the future of general-purpose computing will occur via devices and not PCs.

These devices -- which include tablets and smartphones, of course, but also hybrid PCs of all kinds -- have different requirements than do PCs. They value portability and battery life over raw power. They must be reliable and secure, and not freewheeling environments where you can just download any app you want and potentially harm the OS and other applications. They must be appliance-like, and simple, not complex.

Some people will naturally rail against this future, and the truth is that for the time being, Windows 8 especially will provide access to both environments, the old-school desktop and the new-world Metro. But as more and more people adapt to Metro -- and, of course, competing device platforms such as Android and iOS -- the impetus behind desktop software and hardware development will slow. I’m not sure when or if it will just go away. But it will decline.

Biggest Change That’s Ever Happened to Windows

Everyone knows that the Metro environment in Windows 8 and RT is immature and in need of improvement. And I’ve written before that Microsoft intends to improve this environment well before any future Windows 8 release. But I’m developing a theory -- and to be clear, this is based on nothing more than my own opinion -- that part of these future updates might also include desktop updates, things that will make the desktop work more seamlessly with Metro, further easing the transition.

We’ll get there. In the meantime, just remember that Windows 8 is a huge transition specifically because Microsoft is moving Windows away from the desktop and toward a more mobile future. This is the single biggest change that’s ever happened to Windows -- and yes, I’m including NT in that assessment -- and one that will no doubt leave more than a few users feeling both confused and betrayed. But as with the seven stages of grief, eventually you have to just understand and accept what’s happening. And what’s happening is that Windows is transitioning into a new mobile platform.