QuickOPC.NET (for OPC Classic; not QuickOPC-UA) assemblies contain certain parts in native 32-bit code (for x86 platform) and in native 64-bit code (for x64 platform). QuickOPC.NET uses 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 support in QuickOPC is written fully in managed code, and is not using the mixed mode assemblies.

Any application built with QuickOPC.NET or QuickOPC-UA assemblies 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.