Microsoft officially confirmed that the ARM release of Windows 8 will not run x86 programs. Metro apps on the other hand will allow platform cross-compatibility.
So, what pushed the company not to allow x86 apps to run in the ARM release? Sinofsky explains:
The challenge is very interesting. If we allow the world of X86 application support like that, or based on what we call desktop apps in our start yesterday, then there are real challenges in some of the value proposition for system on a chip, you know, will battery life be as good, for example? Well, those applications aren't written to be really great in the face of limited battery constraints, which is a value proposition of the Metro style apps.
So, we have to be careful that we don't remove the value proposition for those applications. On the other hand, people would say, oh, but you have to let them run because then there's that whole ecosystem. And then if we do let them run, we just brought the perceived negatives of some of the ecosystem. So, people say, great, now it's easy to port viruses and malware and we'll port those.
So, we've taken the approach that we're going to build a bunch of rich capabilities in the operating system that allow devices and peripherals and a broad range of form factors all to run and working with multiple ARM partners on the ARM side, and then Intel and AMD on the system on a chip side, but then focus on the Metro style applications as the opportunity.