Microsoft has released virtualisation software that allows users to run applications in Windows 7 as if they are running in XP. The company said that this would make it easier for applications written for older versions of the OS to run on Windows 7.

The Windows XP Mode Release Candidate is available for public download from the Microsoft Download Center, Microsoft Connect and on the Windows home page.

It also detailed some of the release's changes from earlier versions in a post on the Windows Team Blog. A release candidate in Microsoft's product-development cycle means the product is near completion.

Windows XP Mode is an optional feature of the Windows 7 Professional, Enterprise and Ultimate editions, and is aimed at helping small- and medium-size businesses upgrade to Windows 7 by giving them a virtual Windows XP environment capable of running business and productivity applications compatible with XP.

The feature is similar to Apple's Classic mode, introduced on Mac OS X, that allowed people to run legacy Mac applications on OS X, which was a drastic change to the platform and would not have run older Mac applications without the feature.

Like Mac OS X, Microsoft's Windows Vista also was a major architectural shift from previous versions of Windows, and Microsoft ran into a massive application-incompatibility problem with the OS. This led many people - particularly business users dependent on legacy Windows applications - to stay on XP or downgrade to XP after buying a Vista machine. By the time Vista had been released, XP had been available for more than five years, so even applications build for older versions of the Windows client OS - such as Windows 2000 - run fairly well on it.

When discussing Windows XP Mode publicly, Microsoft executives have said that Windows XP Mode was created to remedy this problem. At the company's recent Worldwide Partner Conference in New Orleans, Microsoft Senior Vice President of Windows Bill Veghte acknowledged that Vista's architectural changes came at the cost of compatibility, and described XP Mode as a way to ensure the same thing would not happen with Windows 7.

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