At the core of OPC Data Client-COM there are COM components that contain reusable library code.  You reference these components from the code of your application, and by instantiating objects from those components and calling methods on them, you gain the OPC functionality.

COM components for OPC “Classic” and OPC UA are implemented in .NET, and exposed to the COM worlds using a COM interop. As such, they are contained in the .NET assemblies described under a corresponding chapter earlier, and installed in a subdirectory called Components\OpcLabs.QuickOpc\net472 under the installation directory of the product.

The assemblies become usable from a COM world by registering them using the Regasm.exe (Assembly Registration Tool), which is a part of .NET Framework. The OPC Data Client installation program registers the assemblies for COM interop automatically.

The Assembly Registration tool reads the metadata within an assembly and adds the necessary entries to the registry, which allows COM clients to create .NET Framework classes transparently. Once a class is registered, any COM client can use it as though the class were a COM class. The class is registered only once, when the assembly is installed. Instances of classes within the assembly cannot be created from COM until they are actually registered.