Microsoft CEO Satya Nadella laid out very clearly on the Microsoft earnings call what the strategy is for Windows, which is to "consolidate overlapping efforts. This means one OS that covers all screen sizes."
He even repeated it: "One, single converged operating system for screens of all sizes."
That's one OS, built by one OS team, for multiple different systems. What's 'one' about that?
Nadella talked of one team with a layered architecture which allows it "to scale the UI across all screen sizes. It allows us to create this notion of universal Windows apps and bring coherence there."
But it's only clear if you're clear on what an operating system is; it's not just the kernel and it’s certainly not just the desktop, and it doesn't run on only one kind of processor.
One Windows isn't just the 'three screens and a cloud' strategy of different devices that might share interface elements or let you use the same account, or have a little bit of Windows inside. That's old Microsoft, many-Windows Microsoft.
At one point, Azure was a fork of Windows with a very different hypervisor; now it's the same OS as Windows Server, with the same Hyper-V hypervisor. But you couldn't take the Azure OS code, put it on a single Xeon server and do anything useful with it because it's designed to do something specific — run a cloud service.
Windows Phone 8 uses the NT kernel, but it isn't the same OS as Windows 8; not only is the user experience very different, but it has different runtimes and (unless you're Microsoft porting across Internet Explorer), you can't build an application that runs on both. Windows Phone 8.1 is closer; it has the WinRT runtime and the concept of universal apps, with the Windows Phone Store and Windows Store being the same underneath. More than 90 percent of the API's are shared between Windows 8.1 Update and Windows Phone 8.1.
This what executive vice president of the Operating Systems group Terry Myerson talked about last December and it's the same One vision of Windows that's been the plan since the One Microsoft re-org. "We want to have one platform that powers all of our devices," Myerson said at the Credit Suisse technology conference, "so that developers can really target the aggregate scale of Microsoft with their investments."
What does that give you? "Enabling developers to write a game which can run on both Xbox and Windows is a very interesting opportunity. Enabling productivity apps that run in the workplace, but also on the phone and tablet."
But even with all the APIs the same, on an OS powered on all those devices by the same kernel, you don't get or want the same thing everywhere, he pointed out.
"Each of our device form factors does require a unique tailored experience, I think, to really delight the customer. So Xbox has got this magical experience on a four-foot screen that I wouldn't want in my pocket on a four-inch screen, and likewise I wouldn't want to scale up Windows Phone to a four-foot screen. So tailoring the experiences to each form factor is another key part of our investment pieces."
The recent job advert for developers in the XAML team building the UI framework for the "one Microsoft OS" talked about "enabling developers to create UI that works well across all of our devices: phones, tablets, PCs and the Xbox".
So, it's one OS on different devices with different experiences. And it doesn't mean Windows RT is going away. For one thing, RT is the basis of Windows Phone now; it's the NT kernel running on ARM with the WinRT runtime. WinRT is how universal apps get on the Windows Store on x86 devices and on Xbox.
For another there's a little phrase in Nadella's comment about the breadth of what Microsoft does that refers to Windows RT and Surface; when he says "from silicon tape out" he's talking about Microsoft making its own ARM chips, which it does for Surface 2.
Surface Mini didn't ship, not because Microsoft doesn't want to keep Windows RT going but because it didn't do anything special enough without the touch version of Office. For Nadella, Microsoft's own hardware is there to show off Microsoft software and services: "All devices will be created with the explicit purpose to light up our digital work and life experiences."
Microsoft certainly isn't dropping ARM for x86; Windows Phone is ARM and Windows RT on Surface is ARM.
Yes, there are going to be a lot of Intel-based tablets, especially small tablets on the cheaper hardware spec that get the free version of Windows. The OEMs know how to knock those out cheaply and they can take advantage of the new 'brokered Windows runtime components' in Windows 8.1.
That's the way a WinRT app on an x86 device can also run Windows desktop code in the background, like all those .NET applications businesses have built over the years. The user sees a WinRT touch app, but the old code is still running. That only works for apps a business sideloads but it could make a desktop-less version of Windows Threshold useful for a lot of businesses.
Because just as the Windows NT kernel that powers the Windows OS on all these devices isn't the operating system, neither is the desktop. The desktop is a shell called EXPLORER.EXE. Try killing the process on Windows; your applications carry on running, but the taskbar and the file explorer and other interface components disappear — then reappear as the operating system restarts the shell, assuming you're on any modern version of Windows. (If not, use Ctrl-Shift-Esc to open Task Manager and File, Run new task to get it all back.) Every operating system has a shell, but the shell is not the operating system.
The most minimal version of the Windows operating system would be the core components known as MinWin; that's the kernel, the basic system services and the TCP/IP stack, with virtualisation that redirects applications calling the tangled old DLLs that used to implement Windows APIs to the new logical DLLs that to the same thing in a tidier way that's easier to slice apart when you need to.
The Windows operating system really is the complete platform that includes all the components and APIs for all the different systems — from phone to PC to tablet to Xbox, to Internet of Things board with sensors, to sewing machines and industrial controllers that assemble Macs.
The Operating Systems Group at Microsoft is busy turning the multiple build systems they had for Windows a and Xbox and Windows Phone into one build system that will take that one Windows and spit out the right build for each platform, screen size and experience.
It's one Windows underneath, but the right Windows for whatever device you're using. Really, it's no more confusing than saying that both cloud and mobile have to be top priority because they're aspects of the same change in thinking.