The whole car is basically a computer on wheels. There are none I would consider the "main" computer, many important computers on the car, for example the engine control unit, the SBC control unit, transmission control unit, and the list goes on and on. What are you trying to do?
The part numbers will vary from car to car, depending on optional equipment, and many are ordered by the VIN number.
Most of the computers at least have some version coding features which need to be set up with the shop computer, and/or transferred over form the previous computer, or set manually if the old one is really junk or missing.
Some of the basic parameters that are set are model version, country code, and right or left hand drive for example. Some of these are set according to how MB directs them to be set, other things can be set according to customer preferences, but usually everything is set according to how it left the factory.