So, Microsoft has made official what was rumored towards the end of last year: the next version of Windows will not only run on x86 processors, but also certain ARM ones. Specifically, it will support certain ARM system-on-chip (SoC) designs from NVIDIA (with its Tegra family), Texas Instruments (with its OMAP 4 family), and Qualcomm (with Snapdragon).
The rationale for this is the claim of growing convergance in computing power across phone, slate, and PCs. SoCs—both x86 and ARM—take this convergence even further, packing ever more power into less space and a smaller power envelope.
The company showed Windows running on ARM hardware, but beyond that, details were scant. We don't know what this "next version" of Windows will be called (though it's presumed to be Windows 8), what it will look like (it is likely to sport a new user interface, but that still hasn't been shown publicly), or when it will arrive (other than within about 24-36 months of the launch of Windows 7).