You can make the 64bit O/S work on Atom based systems but there are several issues:
The first is that the manufacturers do not provide a complete set of 64 bit drivers for components in Atom systems. This means that the peripheral components built into the systems may not work properly. This may include the camera, sound, microphone, touchscreen, Bluetooth, wireless or the video might not be able to display the optimum resolution.
The second is that the 64 bit O/S itself uses a lot of resources so it can address large amounts of memory. The 64 bit O/S is needed to address memory over 3.2 GB and adds no benefits to any system with less. It just doesn’t make a lot of sense to put an O/S that needs a lot of system resources on a resource constrained system. The 32 bit Windows O/S runs great up to 3GB. On an Atom based machine with the current 4GB maximum, the O/S memory overhead of the 64bit version makes it about equal in available memory to a system running the 32 bit version. A dual core Atom, 4GB based system running Windows 7 32 bit O/S is faster at doing most things than a similarly configured system running the 64 bit version.
Why did Microsoft make a 64 bit O/S for Atom based machines then?
A lot of integrators make focused, customized, single use solutions that utilize the Atom processor. Things like firewalls, Internet filters, Routers and wireless access points can be made to run 64 bit O/S on an Atom based system. When creating a single purpose machine the performance can be optimized to make it worth using the 64 bit O/S. A single purpose machine that is designed to run one thing faster in 64bit usually does not need to run the built in components mentioned above such as Bluetooth, camera, etc.
Our users tend to ask their systems to perform a lot of varied functions so in almost all cases there is a much better user experience when running a 32 bit O/S on Atom based systems.
Currently, if you decide to install Windows in 64 bit mode on a CTL Atom based system we do not provide support and cannot provide a full set of drivers.