One of the notable aspects of Microsoft Windows has been the flexibility the architecture has shown through shifts in technology and expansion of customer usage over time. What started out as an operating system for one person working solo with productivity software is now the foundation of a wide array of hardware and software technologies, a spectrum of connected Windows products, and an incredibly flexible approach to computing. With Windows 8, we have reimagined Windows from the chipset to the experience—and bringing this reimagined Windows to the ARM® processor architecture is a significant part of this innovation. Expanding the view of the PC to cover a much wider range of form factors and designs than some think of today is an important part of these efforts. Windows on ARM enables creativity in PC design that, in combination with newly architected features of the Windows OS, will bring to customers new, no-compromise PCs.

This post is about the technical foundation of what we call, for the purposes of this post, Windows on ARM, or WOA. WOA is a new member of the Windows family, much like Windows Server, Windows Embedded, or Windows Phone. As with those products, WOA builds on the foundation of Windows, has a very high degree of commonality and very significant shared code with Windows 8, and will be developed for, sold, and supported as part of the largest computing ecosystem in the world. Today we’ll focus on the development of WOA and introduce some of the features, along with how customers will experience it. As with x86/64 Windows 8, there are still announcements to be made relative to the business and marketing aspects of the product(s). Today’s blog post is about making WOA, not marketing or selling it.

At the same time, while this post is exclusively on our work on WOA, we have had a deeper level of collaboration with Intel and AMD on the full breadth of PC offerings than in any past release. Windows 8 innovations on powerful and richly capable x86/64 processors, and work on new low-power processors such as those that Intel demonstrated at CES, require an equally strong commitment, even larger engineering investment, robust new designs, and improved architecture for Windows across these platforms. While discussing our engineering for ARM processors, it is important to keep in mind that in addition to all of the new work for the ARM platform we have done, much of the work discussed in this post applies directly to the x86/64 platform and Windows 8 as well. We could not be more excited or supportive of the new products from Intel and AMD that will be part of Windows 8—across a full spectrum of PC form factors including tablet, notebook, Ultrabook™, all-in-one, desktop, and more that all take advantage of the new capabilities of Windows 8 while Windows 8 takes advantage of new features in hardware.

Using WOA “out of the box” will feel just like using Windows 8 on x86/64. You will sign in the same way. You will start and launch apps the same way. You will use the new Windows Store the same way. You will have access to the intrinsic capabilities of Windows, from the new Start screen and Metro style apps and Internet Explorer, to peripherals, and if you wish, the Windows desktop with tools like Windows File Explorer and desktop Internet Explorer. It will have the same fast and fluid experience. In other words, we’ve designed WOA to look and feel just like you would expect. WOA enables creativity in PC design that, in combination with newly architected features of the OS, will bring to customers new no-compromise experiences.

As an in-depth engineering dialog, we tend to favor the long form for Building Windows 8 posts, and this post is no exception. It does seem like a good idea to first provide a summary of the important items we are going to cover in detail in this post:

• Windows on ARM, or WOA, is a new member of the Windows family that builds on the foundation of Windows, has a very high degree of commonality and very significant shared code with Windows 8, and will be developed for, sold, and supported as a part of the largest computing ecosystem in the world. We created WOA to enable a new class of PC with unique capabilities and form factors, supported by a new set of partners that expand the ecosystem of which Windows is part.
  • WOA PCs are still under development and our collective goal is for PC makers to ship them the same time as PCs designed for Windows 8 on x86/64. These PCs will be built on unique and innovative hardware platforms provided by NVIDIA, Qualcomm, and Texas Instruments, with a common Windows on ARM OS foundation—all running the same Windows OS binaries, a unique approach for the industry. PC manufacturers are hard at work on PCs designed from the ground up to be great and exclusively for WOA.
    • Metro style apps in the Windows Store can support both WOA and Windows 8 on x86/64. Developers wishing to target WOA do so by writing applications for the WinRT (Windows APIs for building Metro style apps) using the new Visual Studio 11 tools in a variety of languages, including C#/VB/XAML and Jscript/ HTML5. Native code targeting WinRT is also supported using C and C++, which can be targeted across architectures and distributed through the Windows Store. WOA does not support running, emulating, or porting existing x86/64 desktop apps. Code that uses only system or OS services from WinRT can be used within an app and distributed through the Windows Store for both WOA and x86/64. Consumers obtain all software, including device drivers, through the Windows Store and Microsoft Update or Windows Update.
      • WOA can support all new Metro style apps, including apps from Microsoft for mail, calendaring, contacts, photos, and storage. WOA also includes industry-leading support for hardware-accelerated HTML5 with Internet Explorer 10. WOA will provide support for other industry-standard media formats, including those with hardware acceleration and offloading computation, and industry-standard document formats. In all cases, Microsoft seeks to lead in end-user choice and control of what apps to use and what formats to support.
        • WOA includes desktop versions of the new Microsoft Word, Excel, PowerPoint, and OneNote. These new Office applications, codenamed “Office 15”, have been significantly architected for both touch and minimized power/resource consumption, while also being fully-featured for consumers and providing complete document compatibility. WOA supports the Windows desktop experience including File Explorer, Internet Explorer 10 for the desktop, and most other intrinsic Windows desktop features—which have been significantly architected for both touch and minimized power/resource consumption.
          • With WOA you can look forward to integrated, end-to-end products—hardware, firmware and WOA software, all built from the ground up. Building WOA has been an ongoing engineering effort involving Microsoft, ARM licensees, PC makers, and developers of components and peripherals. These efforts spanned a wide array of subsystems that have been newly created or substantially re-architected for WOA. Partners will provide WOA PCs as integrated, end-to-end products that include hardware, firmware, and Windows on ARM software. Windows on ARM software will not be sold or distributed independent of a new WOA PC, just as you would expect from a consumer electronics device that relies on unique and integrated pairings of hardware and software. Over the useful lifetime of the PC, the provided software will be serviced and improved.
            • Around the next milestone release of Windows 8 on x86/64, a limited number of test PCs will be made available to developers and hardware partners in a closed, invitation-only program. These devices will be running the same branch of Windows 8 on x86/64 as we release broadly at that time. These are not samples or hints of forthcoming PCs, but tools for hardware and software engineers running WOA-specific hardware.
              • The Windows Consumer Preview, the beta of Windows 8 on x86/64, will be available for download by the end of February. This next milestone of Windows 8 will be available in several languages and is open for anyone to download.

              This post is organized with the following sections: Working with partners, Providing apps, Engineering for ARM (which will go through the various subsystems), Developing for ARM, Delivering WOA PCs, and finally, Next steps.

              We’ve also prepared a short video demonstrating WOA as described in the post.