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Each server running under UNIX offering a service normally executes as a separate process. When the number of services being offered becomes large, however, this becomes a burden to the system. This is because resources must be allocated to each server process running, even when there are no current requests for the services being offered.
Additionally, it can be observed that most server programs use the same general procedure to create, bind, listen, and accept new client connections. A similar observation can be made for connectionless server operation.