<P> A server may receive requests from many distinct clients in a short period of time . A computer can only perform a limited number of tasks at any moment, and relies on a scheduling system to prioritize incoming requests from clients to accommodate them . To prevent abuse and maximize availability, server software may limit the availability to clients . Denial of service attacks are designed to exploit a server's obligation to process requests by overloading it with excessive request rates . </P> <P> When a bank customer accesses online banking services with a web browser (the client), the client initiates a request to the bank's web server . The customer's login credentials may be stored in a database, and the web server accesses the database server as a client . An application server interprets the returned data by applying the bank's business logic, and provides the output to the web server . Finally, the web server returns the result to the client web browser for display . </P> <P> In each step of this sequence of client--server message exchanges, a computer processes a request and returns data . This is the request - response messaging pattern . When all the requests are met, the sequence is complete and the web browser presents the data to the customer . </P> <P> This example illustrates a design pattern applicable to the client--server model: separation of concerns . </P>

Functions of a server in a client server network