Microsoft Component Technologies – A Summary

OLE Automation
Object Linking and Embedding. Microsoft client-server technology for IPC that allowed an Excel chart to be embedded or linked from a Word document. The shared objects(automation objects) were hosted by an OLE server and could be accessed through an OLE client (automation controller).

COM
COM is Microsoft’s platform for creating software using components – standardized reusable software blocks callable by a variety of client platforms.

What are the features of a component that come to mind -
run-time type discovery (QueryInterface)
loose coupling/late binding (IDispatch)
dynamic creation and destruction (CoCreateInstance)
isolation from the client process (out of process execution)
lifetime management services (Addref-Release)
multi-platform support (e.g. C++,VB,Scripting)

ATL
A set of lightweight template-based C++ classes to simplify COM programming. MFC was heavy weight and couldn’t be used for Internet controls.