Registrationfree

Registration-free COM is a programming technique that allows COM components to be used by applications without the need for them to be registered in the Windows Registry. Normally, COM components require entries in the registry that specify their CLSID (Class Identifier), ProgID (Programmatic Identifier), and the location of their DLL or EXE file. This registration process is typically handled by an installer.

The registration-free COM mechanism leverages the manifest files introduced with Microsoft's Component Object Model. Manifest files are XML documents that describe the assembly and its dependencies. For a COM component to be registration-free, it needs to be deployed as a "side-by-side" assembly. This means that the COM component's DLL and its associated manifest file are placed in the same directory as the application that uses it, or in a known location that the application can access.

The manifest file for a registration-free COM component contains information about the COM classes that the assembly implements, including their CLSIDs and the type of activation they support (in-process or out-of-process). When an application attempts to create an instance of a COM object, the operating system consults the application's manifest and any manifests of its side-by-side assemblies. If the manifest describes the requested COM class, the operating system can activate the component without needing to query the global registry.

This approach offers several advantages. It simplifies deployment as there's no need for a separate registration step. It also helps avoid conflicts between different versions of COM components, as each application can have its own private copy of a component and its manifest. This is particularly useful in scenarios where multiple applications might depend on different versions of the same COM library. Registration-free COM is commonly used with .NET assemblies when they expose COM interfaces.