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Why is it called Windows 10 not Windows 9?

One of the most surprising aspects of yesterday’s Microsoft event was the name of its new operating system: Windows 10. Not Windows 8.2 or Windows 9… but Windows 10. When asked about Windows 10′s name, Windows chief Terry Myerson and Joe Belfiore avoided a direct answer, instead joking about how ‘seven ate nine’ and then lamely saying how the ‘breadth of the product family’ justifies the grandiose name. So, really, why did Microsoft call it Windows 10 instead of Windows 9?

I’ve added two other alternative (conspiracy?) theories on why it might be called Windows 10 rather than Windows 9. I would take these theories with a large pinch of salt — but I’ve included them because they’re just about feasible enough that they might actually be real.

Version numbers, version schmumbers

First of all, it’s important to note that between Windows 3 and Windows 7, versions of Windows were designated by a name rather than a number: 95, 98, NT, Me, 2000, Vista, and so on. When Microsoft announced Windows 7, there was actually a similar amount of disbelief/pushback; after a series of named versions of Windows, it seemed odd to jump back to numbers.


There’s also the odd fact that the name of each Windows release doesn’t actually match the real version number; for example, Windows 8.1 is actually version 6.3 of Windows. Windows 10 is version 6.4. The last time the release name actually matched the version number was Windows NT 4.0, which was released back in 1996. Windows 2000, which was called NT 5.0 during development, was actually version 5.0. Windows XP was version 5.1. Windows Vista was 6.0, Windows 7 was 6.1, Windows 8 was 6.2, and Windows 8.1 is version 6.3. (WinRT, which powers Metro, is a new and separate beast, but it still sits on top of the core Windows kernel.)

Technically, modern versions of Windows are still based on the Vista kernel/code base — including Windows 10, which is actually Windows 6.4. There will be some confusion if/when we eventually reach internal version 7.0, but we’ll cross that bridge when we get there.

Some alternative theories for skipping Windows 9

After publishing this story, some other possible reasons for Microsoft skipping Windows 9 came to light. I am dubious about both of these alternate theories, but they have just enough truthiness in them that I’ll share them with you.

First, an ExtremeTech reader called Benny emailed me to say that the number 9 is considered unlucky in Japan. Microsoft has a big enough presence in Japan that it may have skipped Windows 9 to avoid any weirdness or ill will. Benny says that Trend Micro — a Japanese company — did the same thing a few years ago when it skipped version 9 of its antivirus software.

Second, someone purporting to be a Microsoft developer posted this comment on Reddit


As stupid/amazing as this sounds, it is actually quite feasible that there are still a lot of legacy Desktop apps that use this method (or something similar) to check for Windows 95 or 98. Bear in mind that this is just an example piece of code — some developers will check for the OS name (“Windows…”), some will check for the version number (as discussed in the previous section of this story), and some might use other methods entirely to find out what OS the app is running on.

What’s in a name?

Ultimately, Windows 10 is just a name. Windows 9 probably would’ve made more sense — and I think it’s going to cause a lot of grief with novice users who just don’t understand what happened to Windows 9 — but Windows 10 isn’t any more right or wrong than calling Vista’s successor Windows 7.


A better question to ask now, though, is: Why did Microsoft call it Windows 10 specifically, and not something else? During the unveil event (video embedded above) Myerson gives us a few clues. Starting at around the 2:10 mark, he says: “We know, based on the product that’s coming, and just how different our approach will be overall, it wouldn’t be right to call it Windows 9.” He then talks about how Windows One would make sense with Xbox One, OneDrive, and OneNote, “but unfortunately Windows 1 has been done by the giants that came before us.” And so it seems the only other viable option was Windows 10.

Microsoft’s seemingly arbitrary choice of Windows 10 is an interesting one. It is clearly a strong version number — and it’s also a neat way of distancing it from Windows 8, which Microsoft really wants to brush under the carpet. In fact, this might even be the same trick that Microsoft used to make us forget about Vista: “With a name like Windows 7, it must be very different from Vista…”


What about any similarity to Apple’s Mac OS X? Apple did a similar trick: Its operating systems steadily incremented through System 1-7, then switched to Mac OS 8 and 9, and when it got to OS 10 (X) in 2001 it stopped. Given how Windows 10 is meant to be a single platform for just about every form factor, plus the massive weight and importance that Microsoft is lending to this release, I wouldn’t be surprised if it sticks around for a long time. I wouldn’t be surprised if future versions of Windows — at least for the next few years — are 10, 10.1, 10.2, 10.3, etc. I don’t think Microsoft is intentionally aping Apple with Windows 10, but I’m sure the marketing department is aware of both the positive and negative repercussions of wanting to ride on Apple’s coattails.

So, there you have it: Windows 10 is called Windows 10 because Microsoft says so. I personally think just “Windows” or “Windows X” would’ve been better — but I guess the former got voted down, and the latter is impossible due to Apple’s own OS X.

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