As reported by engadget,
It’s a rough-around-the-edges release, to put it mildly. Microsoft warns that some x64 apps might not run at this stage, and you’re encouraged to install both updated graphics drivers as well as a preview redistributable that lets 64-bit ARM and x64 C++ apps run at the same time. You won’t want to use this Windows 10 preview on a mission-critical machine.
Microsoft is adding x64 emulation at a critical moment. Apple recently released the first Macs based on its in-house ARM silicon, and they already run non-native 64-bit apps with relative ease. That’s a significant advantage for anyone who wants the efficiency benefits of ARM without giving up 64-bit apps they might need. It will be a while before x64 emulation is polished enough to be widely available on Windows 10, but it could make the case for sticking with Microsoft’s platform if you’re comfortable with less-than-ideal performance for some programs.