One Windows, Multiple Form Factors

Posted on March 23, 2015 by Paul Thurrott in Windows 10 with 0

With Windows 10, Microsoft is pushing the notion of “One Windows,” where previously separate OS versions on different types of devices are now converging into a single platform. This visions is part hype and part reality. But I think a better explanation of what’s happening is that Microsoft is simply continuing to evolve the underlying Windows platform with this release.

As it turns out, Microsoft agrees with this explanation. In his Developing for the Windows 10 Hardware Platform session at WinHEC 2015 last week, Microsoft distinguished engineer Don Box explained what One Windows really means.

And it goes like this.

Prior to 2011, the firm had three major variants of Windows (that they feel like discussing, anyway: Windows for PCs, Windows Phone and Xbox 360. Windows for PCs is of course Windows as we’ve always known it, and by 2011, NT had long ago taken over the code base and all of the vestiges of MS-DOS had been removed. Windows Phone—in 2011—was still based on Windows CE. And Xbox 360 was based on a PowerPC fork of NT that no one is comfortable discussing.

These systems were all “Windows.” But they were also all based on different code bases, making interoperability difficult. Box used the example of Internet Explorer, which is available on all three and is in many ways a completely different app on each.

So since 2011, Microsoft has been on a “progression” to bring its code bases together. Windows Phone 8 and Xbox One were based on Windows 8. And then Windows Phone 8.1 was based on Windows 8.1. So Windows, Phone and Xbox were on “the same code path,” as Box put it, but there is “still a fair amount of divergence” between the platforms.

Windows 10 is the next step in this progression. And in addition to Windows for PCs, Phone and Xbox, there are new form factors like Internet of Things (IoT), Surface Hub, and HoloLens that will also be based on the Windows 10 platform.

These form factors are so different that a single OS doesn’t make any sense. But what Microsoft is doing is certainly pragmatic enough: Make enough of the platform common to each OS variant. So what “One Windows” is really about isn’t so much “a single code base,” which is actually pretty impossible, but more common code base across the three platforms.

Put more succinctly, across all of those platforms, Windows 10 will share a common core OS, a common apps platform, and a common store (online service). This is what One Windows really means.

Once you get past the notion of a single OS, you can see how this common platform—”One Windows”—can vary greatly from form factor to form factor. Consider the following slide, which should be familiar to most by now.


Even within the most common personal computing devices, there is a clear differentiation. The devices that will run Windows 10 Mobile—which is based on Windows Phone—all share a default portrait orientation and will run exclusively in full-screen mode with no desktop.


But once you step up to a larger tablet, and then all the way through every type of PC imaginable, you get a default landscape orientation, and the ability to access the desktop and run desktop applications too.


Indeed, the user experience is always tailored for the device. IoT, by definition, is headless. Surface Hub has a unique touch-based UI (and probably the ability to just access Windows 10 for PCs as well). Xbox One and HoloLens each need their own specific user experiences as well. The Xbox One UI will not be a duplicate of that of Windows 10 for PCs. (And Box hinted that there would be future form factors to come in the years ahead. Supporting them is easier because of the work that went into Windows 10.)

“This is the way Windows 10 is built,” Box said, as the following slide appeared.


As you can see, each product line gets its own user experience, and each has some unique features.

Windows for PCs can run desktop Windows applications.

Phones and small tablets feature a “familiar mobile shell,” and phones include both rich telephony and “Windows Phone app compatibility.” Yes, Box very specifically said that existing phones apps will only run on Windows 10 phones, which I think is a mistake. (Maybe Box misspoke.)

Obviously, Xbox One has games interfaces, and Xbox One games specifically.

But underneath this is “One Windows”: the common core OS, app and device platform (including the store backend), and runtimes and frameworks. Obviously, a big chunk of this is aimed at developers, to give them the widest possible reach. And users will benefit too, since they will in some cases be able to buy an app on one platform (say, phone) and get the same app on other platforms (PCs, Xbox) for free. (This is at the discretion of the developer.)

Anyway, One Windows isn’t so much new and different as it is the next step down a path that Microsoft has been on for several years and across multiple Windows versions. I suspect there will be further steps in the future as well.

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