Windows 10 on ARM could run x86 apps seamlessly at native speed

— 10:00 AM on May 16, 2017

Late last year, we heard that Microsoft was working on bringing Windows 10—not Windows RT, or Windows 10 RT, or something like that—over to ARM processors. In December, Qualcomm and Microsoft demonstrated Windows 10 running on a Snapdragon 835 ARM SoC. Now, the company says that not only is Windows 10 running on ARM, but that standard x86 applications can run seamlessly on those CPUs with little performance loss.

Microsoft showed off the developments at its Build 2017 conference last week. The 13-minute video above goes into depth on the subject, but the short version is that users likely shouldn't need to take any special steps while using their ARM-powered Windows machines. Microsoft's ARM Group Program Manager Hari Pulapaka and Director of Development Arun Kushan walk us step-by-step through a demonstration of Windows 10 on ARM, showing proof that it is indeed an ARM chip inside the hardware.

At around 5:30, though, they bring in a real-world situation that would've stymied someone using Microsoft's Windows RT. In this scenario, someone sent the user an archive created using 7-Zip, an application that's not available for ARM processors. Where Windows RT required applications built specifically for that OS, in the demo Pulapaka simply installs the standard version of 7-Zip and opens the archive. If you've ever used Windows RT, that alone should be enough to blow your mind.

So what's going on here? Windows 10 on ARM will run x86 apps through a custom emulator built by Microsoft. Kushan says that when you run an x86 application, the emulator's Dynamic Binary Translator looks at chunks of the code and translates them to ARM64 code, which is then cached in memory or on disk for later use. Microsoft is calling those emulated binaries Compiled Hybrid Executable files, or CHPE for short. That's pronounced "chippie," not like that Neill Blomkamp movie about the robot. All the system calls and communication with the Windows Kernel happen on the ARM side without any emulation. Kushan explains that this allows the operating system to run those x86 applications at "basically native speed."

Previous Windows phones and Surface RT tablets were limited to the applications that developers were willing to re-build specifically for the Windows Store—something most developers opted not to do. This requirement hamstrung adoption of Microsoft's alternative Windows versions over the years, and likely contributed to the near-complete decline of its smartphone business.

Devices with contemporary ARM SoCs like the Snapdragon 835 are generally affordable and pack a powerful punch. Having standard Windows applications run on those devices give Microsoft access to a whole new market of lower-cost hardware that inter-operates seamlessly with existing desktop and laptop computers. We likely won't see high-end users switching off Intel chips anytime soon, but this is a big step forward for Microsoft all the same.

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