If you’re planning to purchase Windows 8, your decision just got simpler.

Microsoft today revealed its lineup of SKUs for the new operating system, which is due to be released before the end of the year.

For PCs built around x86 and x64 processors, the lineup has been trimmed to two. Yes, you read that right. Windows 8 will ship in two editions:

Windows 8 is the default consumer edition, replacing Windows 7 Home Premium. It includes the ability to switch languages on the fly, a feature that was previously available only in the most expensive Enterprise/Ultimate editions.

is the default consumer edition, replacing Windows 7 Home Premium. It includes the ability to switch languages on the fly, a feature that was previously available only in the most expensive Enterprise/Ultimate editions. Windows 8 Pro is a superset of Windows 8, with the addition of BitLocker encryption and support for Encrypting File System, client Hyper-V virtualization, the ability to boot from a virtual hard disk (VHD), the ability to join a Windows domain, support for group policy, and Remote Desktop host capabilities. That complete package of features is currently available only in Windows 7 Ultimate and Enterprise.

Those two editions will be available in retail packages and preinstalled on new PCs by OEMs, and there will be no additional choices available for purchase.

The lineup in retail channels might be simpler, but today's announcement included details about a handful of other special-purpose editions not aimed at the mainstream consumer PC market. If you add in those editions, it's possible to count the number of Windows 8 editions as four, five, or six.

For PCs and tablets built around low-power ARM processors, there will be a single edition, called Windows RT. Although this edition uses the Windows 8 code base and has most of its features, it doesn't include the Windows 8 brand name. In the blog post announcing the details of the Windows 8 release strategy Microsoft carefully avoided that name, noting instead that "Windows RT is the newest member of the Windows family." The product formerly known as Windows on ARM, or WOA, will be available pre-installed on devices by OEMs only. It will not be for sale as a retail product and has no upgrade path to other Windows editions.

Update: In a previous post on the Building Windows 8 blog, Microsoft's Steven Sinofsky made it very clear that Windows RT is not Windows 8:

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... [emphasis in original]

For enterprise customers with Software Assurance agreements, Microsoft will offer a separate edition (not available as a retail package and also not available preinstalled on new PCs). The Enterprise edition is a superset of Windows 8 Pro, with "features for IT organization that enable PC management and deployment, advanced security, virtualization, new mobility scenarios, and much more." Microsoft did not announce additional details of features in the new Enterprise edition and declined a request for comment. Historically, the Enterprise edition is identical to the high-end retail SKU and offers separate access to the Microsoft Desktop Optimization Package (MDOP) as well as some additional licensing rights.

Windows Media Center will be available as a “media pack” add-on to Windows 8 Pro, at an “economical” price point that presumably covers the cost of licensing technology from Dolby Labs and other codec providers. (I had speculated back in September that this would be a a possibility.)

In a blog post announcing the editions, Microsoft also revealed that it plans to offer “a local language-only edition of Windows 8” for distribution in “China and a small set of select emerging markets.” This edition would presumably replace the low-cost Starter Edition, and the single-language restriction would make it more difficult to transfer these low-cost editions into higher-priced Western markets.

Microsoft did not announce any pricing information for any of the Windows 8 editions.

The decision to radically simplify the Windows 8 product lineup is a surprise, but in keeping with a long series of decisions designed to blunt longstanding criticism of Windows. Some Windows 8 rumor trackers, after poking through the Windows 8 registry, had speculated (incorrectly, as it turns out) that Microsoft could release as many as nine flavors of Windows 8.

Windows 7 currently ships in three retail editions (Home Premium, Professional, and Ultimate), with a Starter edition restricted to specific hardware types and a Home Basic edition available in emerging markets.

The new two-edition lineup for Windows 8 is reminiscent of the days of Windows XP, when retail SKUs were limited to Home and Professional. Within a year of XP's launch, though, the XP lineup had sprawled to include OEM-only Tablet and Media Center editions, with a separate 64-bit edition also debuting in 2002 and a Starter edition appearing shortly thereafter.

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