What is DCOM or Distributed COM?

Today's applications have became larger, and many developers want to execute COM components on remote computers instead of only on the local machine. Microsoft's answer is Distributed Component Object Model (DCOM). It extends COM by allowing objects to communicate across a network while preserving the same programming model used for local components.

DCOM uses Microsoft's Remote Procedure Call (RPC) mechanism to activate remote objects and invoke methods. From the developer's perspective, creating a remote object is very similar to creating a local COM object. For example:

Set obj = CreateObject("MyApplication.Component")

Depending on the component configuration, the object may be created locally or on a remote server. DCOM handles the network communication transparently.

Remote activation can also be configured using the DCOM Configuration utility called dcomcnfg.

Administrators can configure launch permissions, access permissions, authentication levels, and the computer where a component should execute. Although DCOM greatly simplifies distributed application development, many things need to work correctly. Things like network access and speed (latency), firewalls, and security settings can make deployment more complex than local COM applications.