A Windows-on-ARM PC is getting closer to reality. Microsoft showed off a prototype mini-desktop with an ARM processor running Windows 10 at last week's Build conference, with the PC running applications like Office.
The PC was shown in a video posted on the Channel 9 website. The presenters reinforced Microsoft's previous message saying that all x86 applications will work on Windows-on-ARM PCs.
Microsoft has maintained that the experience on Windows 10-on-ARM PCs will be similar to x86 laptops, but many questions remain. One revolves around whether Windows 10-on-ARM PCs will support Windows Mixed Reality headsets.
At an Acer event last month, a Microsoft spokesman said, for now, Windows Mixed Reality headsets are configured to support only the x86 instruction set. Microsoft reinforced that position at the Build conference.
Microsoft says PCs will require at a minimum Intel's dual-core Core i5 and an integrated HD 620 GPU to run its Windows Mixed Reality headsets. PC makers like Acer, Asus, Dell, Lenovo, HP, and others will ship headsets. Last month, Acer said the price of its headset will start at US$299.
But from ARM chipmaker Qualcomm's perspective, all x86 apps will run on Windows 10-on-ARM PCs, which are expected later this year. That could include Mixed Reality headsets from working with the PCs.
"There’s nothing that would prohibit it from a hardware standpoint. I just think it’s a function of time," Keith Kressin, senior vice president of product management at Qualcomm Technologies, said two months ago at MWC.
The Windows 10-on-ARM PCs will run on Qualcomm's Snapdragon 835 chip, which has the ingredients to support Mixed Reality headsets. The chip has an integrated GPU that supports 4K video, the latest Bluetooth 5 wireless connectivity, and the latest display ports. Android mobile devices like Samsung's Galaxy S8 handsets with the Snapdragon 835 already are capable of running mobile VR on headsets.
But Windows 10-on-ARM PCs are designed more for mobility than virtual reality, Kressin said. The laptops and 2-in-1s are being designed, in the mold of smartphones, to be super thin and always connected to the internet.
Microsoft has made some clever improvements to bring x86 app support to ARM chips. Windows-on-ARM PCs don't have native support for x86 desktop applications. Instead, x86 apps are funneled through an abstraction layer and CPU emulator to run ARM chips.
Windows PCs with x86 chips typically run code natively on hardware, but the Windows on ARM PCs won't be able to do that. A "dynamic binary translator" will look at chunks of x86 code, which a run-time will then translate to ARM64 code. The ARM64 code will be cached for subsequent use. Emulation can be slow and take up system resources, but Microsoft has developed tools to reduce overhead.
Then, it becomes a question of whether the Windows on ARM emulator can handle the massive graphics and CPU processing power required by Mixed Reality headsets and applications. Microsoft said x86 apps on ARM will be slightly slower than on Intel or AMD PCs.
But there are some possible ways to run Mixed Reality on ARM. Headsets could be connected to Windows on ARM PCs to view VR content in a browser or an app supporting the WebVR specification. WebVR is an open standard and is supported by all major browsers and hardware including Windows Mixed Reality, Oculus Rift, and the HTC Vive headsets. Making Mixed Reality work may come down to whether any supporting headset is released for Windows 10 on ARM PCs.
PC makers are playing it safe with Windows-on-ARM PCs. Dell, Asus, and HP like the idea of a super-slim laptop with cellphone-like cellular connectivity to the internet. But they aren't prematurely announcing hardware as a way to ensure these PCs aren't the next coming of Windows RT, a 2012 OS for ARM-based tablets. Windows RT, based on Windows 8, failed because it didn't run standard x86 applications.