What is COM, DCOM objects in DotNet

Can some please answer this question in detail and also how they are going to be useful in
DotNet

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COM objects require installation on the machine from where it is being used and DCOM requires installation somewhere on the same network.

Any COM object may participate in DCOM transactions. DCOM introduced several improvements/optimizations for distributed environment, such as MULTI_QI (multiple QueryInterface()), security contexts etc.

DCOM demonstrated importance of surrogate process (you cannot run in-proc server on a remote machine. You need a surrogate process to do that.)

DCOM introduced a load balancing.

The fact is dotnet has not replace the COM/DCOM instead it has extended the functionality by introducing new featurs to it.

While dot-NET software can utilize COM components, and COM components can tie into many features of the Dot-NET environment, the two technologies are internally separate. In particular, Dot-NET has been designed to work across the Internet, with firewalls and wide-area networks, whereas DCOM was designed primarily for use on local-area networks.
We can use the legacy COM components from .NET environment and viceversa.Inorder to access a COM component from .NET environment, .NET uses CCW ( COM Callable Wrapper ) object and for accessing a .NET component from COM environment , COM uses RCW( Runtime Callable Wrapper) object.

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The dot net frameworks allow you to build serviced components that can use com+ services. These components of dot net framework runs in the manages execution environment of dot net framework that is share their content with com+ application.

Now the question arise what com+ and what is doing how is its comes in existence. Before com+ comes into existence. COM (Component Object Model) is first programming model that provide component based approach to software development. This component based approach of com allowed us to develop small, logical reusable and stand alone modules that integrates into a single application. But these components could not be display on over network.

So these drawback produce another model that is DCOM (distributes COM). DCOM programming model enabled you to display com components over network and distribute application easily across platforms. DCOM components also help in two-tier client/server applications. These models also have some drawback that helps to development of COM+ approach. What these drawbacks are…

These two-tier architecture helps us to sharing of resources and data but these approach have some drawbacks that are as follows.

The DCOM approach overburdened client computer with the responsibility of performing all processing functions while the server merely acted as traffic controller, helps movement of data to and from the client and server components. So availability of resources was therefore, always a problem and the performance of application suffered. Multiple request of data cause to network traffic. So performance of application decreases.

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