What is Windows 10X? Everything you need to know about Microsoft's dual-screen OS

Microsoft's long-rumored, dual-screen Surface device will run an operating system variant called Windows 10X. So, what is this thing?
Written by Mary Jo Foley, Senior Contributing Editor

Microsoft teased its long-rumored, dual-screen Surface Neo device at its fall event in New York City on Oct. 2. That device will run an operating system variant that Microsoft has christened as "Windows 10X." So, what is this thing?

Here's everything I know -- or at least think I know -- about Windows 10X as of today.

What is Windows 10X? Is it the same thing as the rumored Windows Lite/Santorini that Microsoft watchers have covered for the past year?

For all intents and purposes, yes, Windows 10X is the official name for Windows Lite/Santorini. It is not a new operating system. It's Windows 10, in a more modular form, optimized for dual-screen/foldable devices.

Why is it called 10X? Are we supposed to call it Windows 10 10? 

No. Microsoft execs seem to be calling this Windows 10 X (as in the letter X). Hardware chief Panos Panay used the word "expression" on stage today describing 10X, as in "it's a new expression of Windows 10." So I am guessing that's what the "official" explanation may be for the name. 


What's the connection between Windows 10X and Windows Core OS (WCOS)? 

WCOS is one piece of the underpinnings of Windows 10X. In the past, I (and others) have described WCOS as the successor to Windows OneCore -- Microsoft's attempt to standardize a set of core components in Windows so that they would work across different types of devices. But WCOS is a combination of the OneCore OS pieces, UWP/Web and Win32 app packages, and the composable C-Shell. (See architectural diagram above.) Together, these are the foundational pieces of Windows 10X.

Which Windows devices will ship with Windows 10X?
As officials said today, Surface Neo, the dual-screen Surface device due around holiday 2020, will run Windows 10X. Any new dual-screen and foldable Windows devices from Microsoft partners like Dell, Lenovo, HP, Asus, and others also will likely ship with Windows 10X (and likely not before holiday 2020). Just to keep things confusing, the just-announced Arm-based Surface Pro X cannot run Windows 10X, despite the "X" in both product names.

Does this mean someone -- Microsoft or another OEM -- could technically make a foldable phone running Windows 10X?

In theory, yes. I hear that Windows 10X will work on both dual-screen devices and single 9-inch panes that can fold in half. If someone wanted to call a foldable 10X device a phone because it was running the Microsoft Your Phone app and thus able to receive/make calls from the device via a user's Android phone, I guess it could be marketed as a phone. 

Also: Microsoft Surface event 2019: All the new products announced CNET    

What about HoloLens 2 and Surface Hub 2X? They've been rumored to be among the first WCOS devices. Will they also run Windows 10X?

 HoloLens 2 (expected to start shipping any time now) and Surface Hub 2X (which is due to ship around spring 2020, my sources say) are also using WCOS under the covers. But because they are not dual-screen devices, they won't run Windows 10X.

I also don't believe that Microsoft will enable any existing Windows 10 device to upgrade/downgrade to Windows 10X. This OS is meant for preloading on new/next-generation Windows devices, not current ones.

Will Windows 10X run on Intel and Arm-based devices? 

I hear, at least in its first iterations, Windows 10X will work on Intel only.

Does Windows 10X replace Windows 10 in S Mode (formerly Windows 10S)?

No. Microsoft still seems intent on selling Windows 10 in S Mode to customers who want their devices to run Windows Store apps only. However, Windows 10X will provide some of the same benefits as Windows 10 in S Mode, my sources say, such as reducing "Win Rot," better "Instant On," a reduced attack surface, and provision of more seamless updates.

What type of apps will/won't run on Windows 10X? 

Unlike Windows 10 in S Mode, Windows 10X won't be limited to Store apps only. Windows 10X will be able to run UWP apps, PWAs, web apps, and Win32 apps. The way it will run Win32 apps is by using containers, as I've reported previously when reporting on Windows Lite. 

Although there have been rumors of Android apps running on Surface Neo, I am doubtful that Windows 10X will ship with such a capability enabled. Sure, it could be done with an Android emulator, but I do not think this will be part of the 10X package from Microsoft (at least not out of the gate).

What about the Chromium-based Edge browser? That's a Win32 app, right? (And the most popular app among all users.) So will it need to run in a container?

As far as I know, yes, Chromium-based Edge (Chredge, as it's known among friends) actually will not have to run in the "Vail" container supported by Windows 10X. I hear the team has optimized Chredge by using a shim so that it will work without a container. 


Won't running Win32 apps in containers mean Windows 10X will be a battery hog and less than optimal, performance-wise?

The way the containerization of apps will work with Windows 10X is interesting. Microsoft seemingly will load the Win32 subsystem if and only if a user needs to run a Win32 app. Otherwise, that subsystem won't need to be loaded, keeping the footprint down and performance up. (See architectural diagram above which shows how Win32 apps will work in a container.) 

Also: Photos: Highlights of the Microsoft Surface Pro 7 and the Neo TechRepublic

When will the Windows 10X bits start showing up in Windows 10 test builds? 

Windows Insider testers already have ferreted out mentions of WCOS in existing test builds of Windows 10. But my contacts say that the "real" WCOS/Windows 10X bits won't show up until Windows 10 "Manganese" -- the feature update targeted for delivery in the fall of 2020. That means testers could potentially see these bits once Microsoft starts testing Windows 10 20H2 (possibly late spring/summer 2020).

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