concealment writes "Windows 8 supports all the traditional Windows applications that have been developed over past decades. But the centerpiece of Windows 8 is not its support for legacy applications. With Windows 8, Microsoft wants to develop a whole new ecosystem of applications: touch-friendly, secure, fluidly animated. The new aesthetic was known as Metro, though rumored legal issues have chased the company away from that particular name. These new applications aren't built with the time-honored Windows APIs of yore. They're built with something new: the "Windows Runtime," aka "WinRT."
WinRT isn't just a new library, though it is that in part. More so, it's a whole new infrastructure for building and assembling Windows programs. If Windows 8 is successful—and more specifically, if Metro apps flourish—WinRT will be the foundation on which Windows apps are built for decades to come."
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