Clarifying some confusion from earlier this week, Microsoft has made it clear that Windows 8 tablets and notebooks running ARM processors won’t be able to run apps from the x86 (running Intel and AMD CPUs) version of the OS.

The news, delivered by Windows president Steven Sinofsky during an analyst call this week, means that Windows 8 won’t be fully compatible across all tablets and desktops. It’s a bit of a knock against Windows 8′s attempt to unify desktop and tablet interfaces.

ARM processors typically power smartphones and tablets today because they’re incredibly power efficient. But since the chip architectures are so different, software built for x86 CPUs will need to be recompiled to run on ARM.

Because of this, Windows 8 tablets running x86 chips will have a leg-up against their ARM slate siblings, since they will allow users to seamlessly jump across tablet and desktop apps. Windows 8 ARM tablets, on the other hand, will be limited to what’s available in Microsoft’s App Store.