Distributed Component Object Model

"Dcom" redirects here. For the doctoral degree, see Doctor of Commerce. For other uses, see DCOM (disambiguation).

Distributed Component Object Model (DCOM) is a proprietary Microsoft technology for communication between software components on networked computers. DCOM, which originally was called "Network OLE", extends Microsoft's COM, and provides the communication substrate under Microsoft's COM+ application server infrastructure.

The extension COM into Distributed COM was due to extensive use of DCE/RPC (Distributed Computing Environment/Remote Procedure Calls) – more specifically Microsoft's enhanced version, known as MSRPC. [1]

In terms of the extensions it added to COM, DCOM had to solve the problems of:

  • Marshalling – serializing and deserializing the arguments and return values of method calls "over the wire".
  • Distributed garbage collection – ensuring that references held by clients of interfaces are released when, for example, the client process crashed, or the network connection was lost.
  • Combining significant numbers of objects in the client's browser into a single transmission in order to minimize bandwidth utilization.

One of the key factors in solving these problems is the use of DCE/RPC as the underlying RPC mechanism behind DCOM. DCE/RPC has strictly defined rules regarding marshalling and who is responsible for freeing memory.[2]

DCOM was a major competitor to CORBA.[3] Proponents of both of these technologies saw them as one day becoming the model for code and service-reuse over the Internet. However, the difficulties involved in getting either of these technologies to work over Internet firewalls, and on unknown and insecure machines, meant that normal HTTP requests in combination with web browsers won out over both of them.[4] Microsoft, at one point, attempted to remediate these shortcomings by adding an extra HTTP transport to DCE/RPC called ncacn_http (Network Computing Architecture connection-oriented protocol).[5]

DCOM was publicly launched as a beta for Windows 95 September 18, 1996.[6]

DCOM is supported natively in all versions of Windows starting from Windows 95, and all versions of Windows Server since Windows NT 4.0[7]

  1. ^ "What is Distributed Component Object Model (DCOM)?". WhatIs.com. Retrieved 2022-08-03.
  2. ^ "DCE 1.1: Remote Procedure Call - Introduction to the RPC API". pubs.opengroup.org. Retrieved 2022-08-03.
  3. ^ Nowak, Filip; Qasim, Mohsin. "A Comparison of Distributed Object Technologies CORBA vs DCOM" (PDF). Archived (PDF) from the original on 2017-08-29. {{cite journal}}: Cite journal requires |journal= (help)
  4. ^ "Object Technology Jeff Sutherland: Web Services: Better than CORBA or DCOM?". Retrieved 2022-08-03.
  5. ^ stevewhims. "Remote Procedure Calls Using RPC over HTTP - Win32 apps". docs.microsoft.com. Retrieved 2022-08-03.
  6. ^ Press Release Announcing DCOM Beta
  7. ^ "Distributed Component Object Model (DCOM) Remote Protocol" (PDF). Microsoft - Distributed Component Object Model (DCOM) Remote Protocol. June 25, 2021. Archived (PDF) from the original on 2021-05-09. Retrieved August 3, 2022.