OPC Studio components for OPC Classic (not for OPC XML or OPC UA) assemblies contain certain parts in native 32-bit code (for x86 platform) and in native 64-bit code (for x64 platform). OPC Studio componenys use a special technique to load the so-called mixed mode assemblies (assemblies that contain both managed and native code) for a proper processor architecture.
OPC XML-DA and OPC UA support in OPC Studio is written fully in managed code, and is not using the mixed mode assemblies.
Any application based on OPC Studio components can also be run on 32-bit Windows, or on 64-bit Windows for x64 processors. By default, such applications run as 32-bit processes or 32-bit machines and as 64-bit processes on 64-bit machines. You can also build your code specifically for x86 or x64 platform, if you have such need.