Microsoft plans to release a flavor of Windows 8, the next version of the flagship operating system, on ARM chips at the same time it releases one for the so-called x86 chips that power traditional PCs.
That was an open question ever since Microsoft previewed Windows 8 last September. And it's important because the ARM version of the new operating system will be the one that powers many of the tablets that Microsoft hopes will compete with Apple's industry-leading iPads.
In a blog post today, Windows President Steven Sinofsky said "our collective goal is for PC makers to ship (Windows on ARM devices) the same time" as more conventional Windows PCs debut.
Sinofsky did not disclose the target launch date, though most analysts expect the new operating system to arrive before the end of this year, and possibly in time for the back-to-school sales season at the end of summer.
Sinofsky also revealed that Microsoft will ship a version of its upcoming productivity suite, code-named Office 15, for the ARM version of Windows 8. Those versions of Word, Excel, PowerPoint, and OneNote have been designed to consume less power and will be touch-enabled, important features for tablet applications.
Sinofsky also noted that Windows on ARM will support the traditional Windows desktop experience for File Explorer, Internet Explorer 10 for the desktop, and "most other intrinsic Windows desktop features." Like the productivity apps, all those intrinsic features have also been designed for touch and minimized power and resource consumption, Sinofsky wrote.
A key to Windows' success on the tablet will be the level to which developers and consumers embrace the Metro user interface that Microsoft is relying on for the touch experience. Sinofsky noted that the ARM version of Windows 8 will run all Metro-style apps. And he wrote that Microsoft will include ones for mail, calendaring, contacts, photos, and storage.
One of the biggest challenges for Windows 8 is managing the transition of Windows to the ARM system-on-a-chip architecture. That architecture enables devices to be thinner and lighter than ones using the traditional x86 chips. That means that slim and sleek tablets will be able to run the new operating system.
But because the chip architecture is different, Windows 8 on ARM won't be able to run some legacy Windows applications unless programmers go through the bother of porting those applications. That could be a huge impediment to some users that want backward compatibility for Windows.
That's why Sinofsky has gone into great detail in his lengthy blog post laying out details of Windows 8 on ARM. He notes that Windows on ARM will only come pre-installed on devices. Consumers won't be able to download a version of the operating system to existing machines. That's because the ARM architecture is not standardized; the software on each device is unique to it.
Updated at 11:30 a.m. PT with additional details and analysis.