Microsoft revealed lots more details about the ARM edition of Windows 8, you can read it over here.
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.