DCOM is Distributed COM, a standard backed by Microsoft. The idea here is that it is a flavor of COM that takes into account how items that you may be acessing invisibly may be on other machines over the wire. Making RPC calls versus LPC calls can be quite expensive in the performance department.

DCOM is one of the main reasons why each true COM method returns an HRESULT (and information into an outward bound pointer). Because you must have a way for a network error to fail out without actually calling the function, returning an HRESULT is better than strange return codes for each type of object or interface. This lets you run SUCCEEDED and FAILED macros against it to determine the base success of the function call, without actually hanging because the actual code to be run is elsewhere.