Ever since Microsoft announced that full Windows 10 would be coming to ARM , many Windows phone fans have assumed this means phones like the Lumia 950 and Lumia 950 XL will be getting an update to full Windows 10. File this one under "totally obvious," but today Microsoft's Joe Belfiore confirmed that existing Windows phones won't be getting full Windows 10 on ARM.

Joe Belfiore provided a rather technical and insightful explanation as to why existing phones won't be able to run full Windows 10 on ARM during the Windows Insider Mixer Broadcast (47:20 minute mark) :

The Windows 10 on ARM effort is about enabling the PC experience on devices that are built on ARM so that they're connected all the time and have great battery life. So the experience is a desktop PC experience, it's not a phone-like experience. For phone-like experiences on ARM, we have Windows 10 Mobile. What Windows 10 on ARM is, is a desktop-like experience so that you get the battery life that ARM processors tend to have. The other thing that's interesting about this is that in all cases where you build ARM software, it's not so easy to just put it on another device. The OS intermingles with what's called the BSP (board support package), and that's how the software talks to the SoC. There's special work that has to be done to get the OS talking to the BSP, talking to the SoC, so it's not like the PC ecosystem where we write an OS in the same binaries that run on lots of different PCs. With ARM devices with SoC, you have to more closely target it. So that is often the case why it's more challenging for us to get updates to a wide range of ARM devices. They're all quite different, which adds delay, and as the number of people using those devices gets smaller, it unfortunately makes less sense for us to invest more time and energy in that.

In short, Belfiore explains that the full Windows 10 on ARM effort is about enabling great battery life and sleep on ARM based laptops and tablets, and not about bringing full Windows 10 to phones. Now of course, this doesn't mean Microsoft isn't working on something for phones. Rumor has it, Microsoft is planning yet another attempt at Windows phone, that may show up as early as next year.

We believe that this next attempt at phones won't be launching for existing handsets however, which means devices like the Lumia 950 will be keeping with Windows 10 Mobile. We do know that CShell will play a big roll part in it, but outside of that not much else is known about the project.

Full Windows 10 on ARM will be launching on tablets and laptops with Snapdragon 835 processors later this year. In the meantime, are you interested in buying a device with Windows 10 powered by an ARM processor?