A COM and Registry review staring CLSID, TypeLib, Interface and AppID

If you are working with COM there are several registry entries that are important and that you need to understand. I will try in this post to clarify them. But before that, let’s enumerate the three possible COM server scenarios. (As a side note, a COM server is a DLL or EXE can contains one or more COM objects; a client is an entity that uses a COM object, which means a COM server can also be the client of another COM server.)

inproc: the COM server is loaded into the client process; in this case accessing the COM methods is as simple as using an interface pointer when the client and the in-proc server are in the same thread
local: the COM server and the client are loaded in different processes on the same machine; communication is achieved with the use of proxies and stubs via Lightweight RPC
remote: the COM server and the client are loaded in different processes on different machines; communication is achieved with the use of proxies and stubs via RPC

In order for the COM Library to be able to locate and instantiate the COM objects correctly, different information is stored in the Windows Registry. The most important information is located under the keys CLSID, TypeLib, Interface and AppID from HKEY_CLASSES_ROOT. The images below show examples for IIS.

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