Client and Server : Your PC, if connected to a LAN, is able to print a file on a printer which is located far away from you, but on the same network. Through your networked PC you can send a request to a server on the same network to print the file on the specified printer. We may now be able to define client/server system as an architecture in which your PC (the client) is the requesting machine and the server is the serving machine, both of which are connected via a LAN or a wide area network (WAN). The client/server technology is responsible for changing the entire scenario of computing and enabling migration from centralised minicomputers and mainframes to networks of desktop computers.
In a client/server system, the client processes the user interface with the help of any popular operating systems say, Windows, Mac, etc, and performs some or all of the application processes. Servers with different applications may be of high-end PCs to mainframes. A database server maintains the databases and processes requests from the client to extract data from the database or to update the database. An application server provides additional business processing for the clients. In a typical LAN environment, servers are widely used to store data and programs and share those files with your PC known as client. In this case, the servers act as remote disk drives to the clients. It also provides file-sharing services, but this scenario does not embody the real meaning of client/server. The key concept of client/server is that both take on some of the application processing. Figure depicts the architecture of client/server systems.