Windows 10 on Arm: What you need to know before you buy a Surface Pro X

Repeat after me: Windows 10 on Arm is not Windows RT. It’s also not the Windows 10 you know. Before you order an Arm-powered Windows device like the new Surface Pro X, read this.
Written by Ed Bott, Senior Contributing Editor

One of the most eagerly anticipated announcements from Microsoft's Surface event in New York City last week was the Surface Pro X. The latest member of the successful Surface Pro family is powered by an Arm processor, which should translate into a dramatically longer battery life and easy LTE connectivity.

Its other distinguishing factor is likely to be consumer confusion, at least if my inbox is an indicator. And that confusion is perfectly understandable. The very first Surface device, Surface RT, was powered by an Nvidia Arm processor, so it's easy to confuse Windows on Arm with its predecessor, Windows RT, which was written for that device.

Stop right there.

Repeat after me: Windows 10 on Arm is not Windows RT. That ancient (at least in tech terms) ancestor was limited to apps in the Microsoft Store, plus a specially compiled version of Microsoft Office. By contrast, Windows 10 on Arm is a full-fledged member of the Windows 10 family, capable of running most Windows desktop apps unmodified.

The biggest restriction, at least for now, is that those desktop apps run in a 32-bit emulator, even though those Arm processors are 64-bit. That can cause a few minor headaches, but it's hardly a dealbreaker.

If you expect an Arm-based Windows laptop to match up in every detail with a conventional Intel-based PC, you might be disappointed. But if you think of it instead as a companion mobile device that does almost everything a conventional laptop can do while getting roughly double the battery life, the value proposition becomes clearer.

To understand where the Surface Pro X fits in this, it helps to understand how we got here.

A brief history of the Always Connected PC

Microsoft announced its intentions to bring Windows 10 to Arm PCs back in 2016, and the first of these so-called Always Connected PCs were announced a year later, at the Qualcomm Snapdragon Tech Summit in late 2017.

By that time, Windows RT was a distant memory. Microsoft had instead devoted a massive amount of development resources to making Windows 10 work on Arm processors. Much of that work was done in the service of Windows 10 Mobile, but because that now-deprecated product shared the same core as Windows 10 on PCs, it's still of value.

Windows 10 on Arm support arrived with Windows 10 version 1709, with devices running that version available for sale in mid-2018.

Those first-generation machines delivered a less-than-impressive experience, but hardware upgrades for the second generation, announced in late 2018, resulted in noticeably improved performance. For the past six months, I've been using one of those second-generation Windows on Arm PCs, the Lenovo C630, which is powered by a Qualcomm Snapdragon 850 processor. It's not perfect, and I wouldn't recommend it unless you understand its limitations. But on balance it's been a worthwhile traveling companion, and it's helped me understand exactly how Windows on Arm works.


The Windows 10 About box correctly identifies the Arm processor in this device

Even if you don't have ready access to one of these devices, you can still read the official Windows 10 on Arm documentation. It's mostly aimed at developers, but it also has some excellent reference material that explains how the platform works, with links to an interesting section on how x86 emulation works.

This section on apps and experiences is particularly worth reading:

Windows 10 on ARM runs all x86, ARM32, and ARM64 UWP apps from the Microsoft Store. ARM32 and ARM64 apps run natively without any emulation, while x86 apps run under emulation.


In addition to UWP apps, Windows 10 on ARM can also run your x86 Win32 apps (such as Adobe Reader) unmodified, with good performance and seamless user experience, just like any PC. These x86 Win32 apps don't have to recompiled for ARM and don't even realize they are running on ARM processor. Note that 64-bit x64 Win32 apps are not supported but the vast majority of apps all have x86 versions of their apps, so from a user perspective, just choose the 32 bit x86 installer to run on the Windows on ARM PC.

Note that these limitations also apply to device drivers, which have to be compiled for Arm. For some 32-bit apps that have performance or other issues related to emulation, you can use the built-in Program Compatibility Troubleshooter on a Windows 10 on Arm device to tweak compatibility settings.

Windows on Arm in action

Nothing about the C630 hardware looks any different from a standard Intel-based laptop, except perhaps for the SIM slot on the left side, behind the second USB Type-C connector. (This device also supports the software-only eSIM capability, which unlocks some of the device's more interesting connectivity features.)

Likewise, after booting up this device, installing Office 365, and running through a standard set of productivity tasks, you will not notice anything out of the ordinary. All the built-in system tools and settings are familiar, the system drive is encrypted by BitLocker, and Plug and Play devices work exactly as expected. I even upgraded the preinstalled Windows 10 Home in S mode to Windows 10 Enterprise without issues.

The single gotcha in all this is that the x86 emulation supports only 32-bit desktop apps. Built-in Windows apps, including Explorer.exe, are full 64-bit apps, as are UWP apps compiled for Arm and delivered through the Store. But 64-bit Windows desktop apps won't install, even if they're repackaged and offered through the Windows Store.

That restriction can cause some confusion, especially when websites automatically offer a 64-bit version of a Windows desktop program or device driver. In that case, you might have to do some digging to discover and download the 32-bit version.

That's less of an issue than it used to be. Both Mozilla Firefox and Google Chrome, for example, offer the correct 32-bit edition when you visit their download pages on a PC running Windows 10 on Arm. So does Microsoft Office 365. You're especially likely to encounter this problem with older Windows desktop programs and utilities that don't check the Windows version correctly.


On a device running Windows 10 on Arm, Google offers the correct Chrome version

You'll have a much bigger problem with apps that are only available in 64-bit versions. The only way to run Adobe's Creative Cloud apps, for example, is to sign in on Adobe's website and see which of the 2018 apps are available in 32-bit versions. Maybe that's one reason why Adobe was on stage with Microsoft announcing that its Fresco drawing/painting app, released last month for iPad Pro and Apple Pencil, would be available on the Surface Pro X.


Microsoft claims the Surface Pro X will get "up to 13 hours of typical device usage."

Image credit: Microsoft

Likewise, my preferred Twitter app, Tweeten, is available only in a 64-bit Windows version, available as a standalone download or via the Windows Store. On this device, neither option will work.

Interestingly, Microsoft Edge (the original version, included as the default browser with Windows 10 versions 1909 and earlier) runs as a 64-bit native ARM app. The new Microsoft Edge, based on the Chromium open source engine and available as a beta release now, runs as a 32-bit emulated Win32 app. Presumably, the official release of the new Edge-on-Chromium browser will be available as a native 64-bit app for Windows 10 on Arm.

When my colleague Chris Duckett looked at the Arm-powered Samsung Galaxy Book2 a few months ago, he noted that "installing games from Steam is an absolute crapshoot, they might work, they might not." That Samsung device was hobbled by memory starvation, with a default configuration of only 4GB of RAM and a list price of $1,000. By contrast, the Lenovo C630 includes 8GB of RAM and sells for around $600, making it a much better value.

Still, even with the proper resources, the overhead of emulation and the relatively weak graphics on an Arm-based PC mean that performance is an issue for anything beyond basic productivity tasks and video playback. If you accept that limitation as a reasonable trade-off for a much longer battery life, you'll be fine with an Arm-based PC. If, on the other hand, you find yourself annoyed by delays of a few hundred milliseconds here and a half-second there, well, don't say I didn't warn you.

The Arm advantage

The two biggest advantages of the Arm platform, in my experience, are battery life and connectivity. That shouldn't be a surprise; the Arm platform was, after all, designed for use in mobile devices, where those attributes are absolutely foundational.

I ran a battery report using the Windows 10 powercfg utility to get a precise measurement of long-term battery usage trends on the C630. The average battery life over that period was impressive, at just a few seconds short of 11 hours. In practice, that translates into 18 hours of steady use with occasional breaks.

Update: In a week of steady usage since updating to the Release Preview of Windows 10 version 1909, the C630 reports average usage per charge of 14 hours 57 minutes. Its standby performance is especially impressive, using only 3-4 percent of battery over a 12 hour period.

As for connectivity, the C630 offers both a standard SIM slot and eSIM capability. In addition, support for LTE connectivity is built into the operating system, with direct links available for global data providers that work well with Windows 10.


A sample of European data plans offered through the Windows 10 interface

On this Lenovo device, I can use a conventional physical SIM for access to data in the US and then switch to the eSIM to access an LTE data plan overseas. For an upcoming trip to Spain, for example, I plan to purchase a package of 10GB of LTE data, good for 30 days, from Ubigi; that coverage uses the Orange Spain and Yoigo networks.

Over the best six months, I've tested the built-in LTE with data-only SIMs from a handful of US-based carriers, including AT&T, Verizon, and Google Fi (which uses the T-Mobile network exclusively for this application, rather than the multi-network approach it uses on Fi-compatible phones). I've also tried Ubigi's service in the US, where a one-day, 500 MB package costs $5 and a 2GB monthly package costs $69 for six months; the coverage was surprisingly strong.

The biggest advantage of built-in LTE over a tethered mobile phone is that it doesn't require the friction of turning tethering on or off, and it doesn't affect battery life on the phone, either. Windows 10 can also automatically switch between LTE and Wi-Fi networks based on their relative strength; by contrast, tethering to a mobile phone requires choosing that network over any other.


Use the toggle at the top of this box to flip between the physical SIM and eSIM.

Microsoft has already shipped two Surface models with Advanced LTE support, so that technology should work as expected. It remains to be seen how the custom Microsoft SQ1 Arm chip (developed in partnership with Qualcomm) will affect battery life. Microsoft claims that the Surface Pro X will get "up to 13 hours of typical device usage," which is more than the "up to 10.5 hours of typical device usage" it promises for the Surface Pro 7.

It's worth noting that the "typical device usage" metric is a noteworthy change from previous Surface devices. The Surface Pro 6, for example, claimed "up to 13.5 hours of local video playback." Is the newer measurement more likely to reflect observed usage? Stay tuned.

A brief history of Microsoft's Surface: Missteps and successes

Disclosure: ZDNet may earn a commission from some of the products featured on this page. Neither the author nor ZDNet were compensated for this independent review.

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