actually COM means component object model, but this raises 
the problem of versioning known as DLL conflicts. so dot 
net uses other functionalities to avoid it..

Component Object Model is a method to facilitate 
communication between different applications and languages.
The following steps explain the way to create the COM 
server in C#: 

Create a new Class Library project. 
Create a new interface, say IManagedInterface, and declare 
the methods required. Then provide the Guid (this is the 
IID) for the interface using the GuidAttribute defined in 
System.Runtime.InteropServices. The Guid can be created 
using the Guidgen.exe. [Guid("3B515E51-0860-48ae-B49C-
05DF356CDF4B")] 
Define a class that implements this interface. Again 
provide the Guid (this is the CLSID) for this class also. 
Mark the assembly as ComVisible. For this go to 
AssemblyInfo.cs file and add the following statement 
[assembly: ComVisible (true)]. This gives the accessibility 
of all types within the assembly to COM. 
Build the project. This will generate an assembly in the 
output path. Now register the assembly using regasm.exe (a 
tool provided with the .NET Framework)- regasm 
\bin\debug\ComInDotNet.dll \tlb:ComInDotNet.tlb This will 
create a TLB file after registration. 
Alternatively this can be done in the Project properties -> 
Build -> check the Register for COM interop. 
The COM server is ready. Now a client has to be created. It 
can be in any language. If the client is .NET, just add the 
above created COM assembly as reference and use it.