COM: Component Object Model
the basis of OLE (Object Linking and Embedding) and Active X technologies is the Microsoft software component model. COM components are encapsulated objects that have a set of structured interfaces. This standardization enables different applications or components to communicate freely with one another.
DCOM : Distributed Component Object Model
Distributed Component Object Model provides distributed services to COM. Such services allows various components to communicate easily across a network. As a single vendor standard DCOM represents a uniform interoperability mechanism.