Why Windows 10?

In other words, what happened to Windows 9?

Introduction

Did Microsoft go from Windows 7 in 2009, to Windows 8 in 2012, straight to Windows 10?

Yes. You didn't miss Windows 9. There's no such thing. Naturally, computer users and IT pros are curious why.

Possible Explanations

Microsoft has not given any specific explanation. Sure, they've made statements, but they sound more like politicians, saying things like this, when asked about it (from Gizmodo):

That's not much of an explanation. Of course, the Internet is awash in theories to explain this better. Here's an interesting one: Some application programs check the version of Windows you're running to assess what capabilities and services of Windows are available for the program to utilize. Remember Windows 95 and Windows 98? Well, the architecture of those versions were so similar that some programmers of Windows applications may have simply looked to see if the Windows version reported by your computer started with "Windows 9" to identify either of those operating systems in an efficient manner. You can see where this would be a problem! If the latest version of Windows were called Windows 9, then theoretically some existing programs, which use this method to check if they're on Windows 95 or Windows 98, would misidentify what version of Windows they're running on if you tried to run them in Windows 9.

However, no one has posted evidence of a program that actually checks your Windows version that way. Also, for reasons we won't get into, any such program probably would not function properly on a modern version of Windows, even if it didn't get confused about what version it was running on. So, this theory is amusing, but probably not a real consideration.

The real reason probably has to do with the new model of updates and upgrades introduced with Windows 10, which Microsoft has termed "Windows-as-a-Service". "As-a-Service" is a designation that, for many years, has applied to applications you pay for on a monthly basis, and which are stored entirely on the application provider's servers (as opposed to being installed on your computer or device). For the most part, these applications are continually and incrementally updated. Well, Microsoft is not going to charge subscription fees for continuing to use Windows (at least not yet), and Windows does install directly on your computer or device. So in those respects it's still like regular software, and not a "service". But, once you're on Windows 10, new features, which are usually saved up for major version upgrades, will be rolled out as updates every few months, and Microsoft intends to update Windows only in this manner for as long as the model can hold up. So, in a word, the era of the big product launch is over. Gone are the days of the new name and logo every few years for the latest, greatest version of Windows.

Microsoft's statements support this as well. In early 2015, before the launch of Windows 10, a Microsoft employee declared that Windows 10 is "the last version of Windows". Microsoft, in a statement to The Verge in response to queries about this, didn't say as much, but they didn't refute it. While they said they won't speak to "future branding" (meaning the version numbers and monikers), they did say that "Windows will be delivered as a service bringing new innovations and updates in an ongoing manner", and that Microsoft "look[s] forward to a long future of Windows innovations."

Conclusion

This all seems to mean there will no longer be any new names (NT, XP, Me, Vista), years (95, 98, 2000), or version numbers (3.1, 7, 8) attached to Windows. It's just Windows forever. Given that we need some kind of label to identify this current Windows from the old ones, a round and perfect number such as 10 is much better than leaving us hanging on 9.

Of course, Microsoft will have to deal with what to call it (including whether to call it Windows at all any more) once our computers and mobile devices (and whatever else is to be invented) have changed so much that something completely new is required. We'll see what happens then!