Windows-as-a-Service has been rumored for quite a while, and most times jokingly because of Microsoft's ability to turn everything into a service for the past few years. Software-as-a-Service (SaaS), Platform-as-a-Service (PaaS), Infrastructure-as-a-Service (IaaS), and so on, have become a very real part of the Cloud vernacular. So, when Microsoft implored us to consider Windows 10 a sort of Windows-as-a-Service during its latest Windows 10 event, I thought the company had finally owned up to the joke.

And, without going into too much detail to alleviate any post-event questions, both Terry Myerson and Satya Nadella stated how important and monumental Windows-as-a-Service will become.

Here's what we know.

Windows-as-a-Service means that once customers install Windows 10, they will essentially be registered with Microsoft to receive rolling, free feature additions, improvements, and updates. This is not too far off course from what we experience today with Windows Update, and this updating mechanism will mostly likely continue to be the vehicle to make this happen for Windows 10. Microsoft has been notorious over the last couple years silently including new features in some of its updates almost as if it was testing the waters for what Windows 10 will provide.

The difference with Windows 10 is that this operating system version could possibly represent the very last major Windows release. Which brings us to Versionless Windows. Whether you install Windows 10 when released, buy a new PC with Windows 10 pre-installed, or decide to upgrade later on, it will always be Windows 10. No new major version numbers and you'll only be able to tell the Build you're using by locating the features that exist on your particular installation. I've talked about this before (over on WindowITPro) but, Myerson made it semi-clear in a statement on the Windows blog yesterday

We'll deliver new features when they're ready, not waiting for the next major release. We think of Windows as a Service -- in fact, one could reasonably think of Windows in the next couple of years as one of the largest Internet services on the planet. And just like any Internet service, the idea of asking 'What version are you on?' will cease to make sense."

The cutting question still remains: "What will it cost?"

We already know that Windows 7, Windows 8, Windows 8.1, and Windows Phone 8.1 users will get the upgrade to Windows 10 for free (for a year), but what happens after that? If Office 365 is any indicator, Windows-as-a-Service sounds like subscription service where you shell out a year's worth of service and can install on multiple devices (which, incidentally, also applies to tablets and smartphones).

Microsoft doesn't seem ready to provide pricing details yet and it's not clear what revenue model the company will apply here, but it does represent a huge shift in the way Windows is purchased, presented, and delivered. Licensing experts should have a field day with this one.

On the other side of the coin, businesses that currently deploy standard Windows images across the company and test and stage updates might have to relinquish that control and allow Microsoft to do the work. That's not something they take lightly, and would require a major shift in operations and IT mindset.