Microsoft Confirms x86 Apps Won't Run on ARM Windows 8

Microsoft officials clarified Wednesday that when they say existing Windows apps will be compatible with Windows 8, they mean on x86 chip architectures.

With the release of the technical preview of Windows 8 this week, Microsoft officials made much about the fact that the next generation operating system will run on two very different chip architectures instead of just one, and they made an effort to reassure developers and customers that applications will be compatible with previous versions of Windows.

"Everything that runs on Windows 7 will run on Windows 8," Steven Sinofsky, president of Microsoft's (NASDAQ: MSFT) Windows and Windows Live Division, told attendees at the company's Build conference in Anaheim on Tuesday when he announced the release of the Windows 8 technical preview.

The next day, answering a question raised during the company's annual Financial Analysts Meeting (FAM), Sinofsky needed to clarify his compatibility promise, although many technical analysts already understood.

Windows 7 applications will be compatible with Windows 8 when it is running on x86 chip architectures, but won't run on Windows 8 running on ARM Holdings' system-on-a-chip architectures. The reason is that the chips themselves are very different from each other.

"We've been very clear since the very first CES [Consumer Electronics Show] demos [in January] and forward that the ARM product won't run any x86 applications," Sinofsky told the analysts. Microsoft initially demonstrated Windows 8 running on ARM processors at CES in Las Vegas in January.

The issue of whether or not x86 Windows applications would run on ARM CPUs surfaced last spring when Intel executive Renee James told analysts that the chip maker believed Microsoft would need to make multiple ports of Windows 8 to support both ARM and x86 processors.

Microsoft responded that Intel was mistaken but never challenged the question of incompatibilities in the two chips' architectures and applications written for them.

In fact, supporting two chips is a risky bet for Microsoft, since customers have grown accustomed to Windows running only on Intel architectures. While x86 has been the standard for PCs and laptops, ARM is the dominant architecture for mobile phones around the world.

Intel architecture processors are designed for high-performance, virtualization, and support for large amounts of memory, while ARM processors are designed for small form factors and low power usage. Microsoft also already has a separate operating system that it is trying to establish in the mobile space -- Windows Phone.

The differences between x86 and ARM architectures also point up reasons why Windows Server 8, the server version of the new system, which was also released as a technical preview this week, will only be available on x86 chips.

"Windows Server 8, like Windows Server 2008 R2, is a 64-bit operating system, and virtualization is a key capability our customers look for. At this time, there are no plans for Windows Server to expand support to additional architectures beyond x86. But as the technology landscape expands, we will continue to look at customer demand to ensure that we have the most compelling server operating system to offer," Amy Barzdukas, general manager of the Microsoft Server and Tools Business , said in an email to

Stuart J. Johnston is a contributing editor at, the news service of, the network for technology professionals. Follow him on Twitter @stuartj1000.

Tags: Intel, Windows 7, Windows 8, x86, ARM

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