All of Chief Architect software comes in 2 flavors, 32 bit and 64 bit, the user decides which version they want.
32 bit will run on a 64 bit machine, 64 bit will not run on 32 bit machine.
The operating system itself is 32 bit unless the user changes it to 64 bit.
As for legacy software, you have to tell windows to run that software in compatibility mode.