I have read it's one ISO for all platforms, each activated with an activation key. Windows has only been 64 bit from Win 7 64 forward. There was no 32 bit Windows 8.
The Atom tablets run 32-bit Windows 8.x. While Atom's may be x64 capable, they're typically given a x86/32-bit install for whatever reason. (Source: My Dell)
my concern then becomes driver compatibility