Basic Concepts about Client and Sever System
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Client–server model is a distributed application structure that partitions tasks or workloads between the providers of a resource or service, called servers, and service requesters, called clients [1].
Often clients and servers communicate over a computer network on separate hardware,
but both client and server may reside in the same system. A server host runs one or more server programs which share their resources with clients.
A client does not share any of its resources, but requests a server's content or service function. Clients therefore initiate communication sessions with servers which await incoming requests.
Examples of computer applications that use the client–server model are Email, network printing, and the World Wide Web.
The client-server characteristic describes the relationship of cooperating programs in an application. The server component provides a function or service to one or many clients, which initiate requests for such services. Servers are classified by the services they provide.
For example, a web server serves web pages and a file server serves computer files.
A shared resource may be any of the server computer's software and electronic components,
from programs and data to processors and storage devices. The sharing of resources of a server constitutes a service
Whether a computer is a client, a server, or both, is determined by the nature of the application that requires the service functions.
For example, a single computer can run web server and file server software at the same time to serve different data to clients making different kinds of requests.
Client software can also communicate with server software within the same computer[2]. Communication between servers, such as to synchronize data,
is sometimes called inter-server or server-to-server communication.
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.
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.
This example illustrates a design pattern applicable to the client–server model: separation of concerns.
Further information: History of personal computers, Decentralized computing, and Computer cluster
The client–server model does not dictate that server-hosts must have more resources than client-hosts.
Rather, it enables any general-purpose computer to extend its capabilities by using the shared resources of other hosts. Centralized computing,
however, specifically allocates a large amount of resources to a small number of computers.
The more computation is offloaded from client-hosts to the central computers, the simpler the client-hosts can be.[10]
It relies heavily on network resources (servers and infrastructure) for computation and storage.
A diskless node loads even its operating system from the network, and a computer terminal has no operating system at all;
it is only an input/output interface to the server. In contrast, a fat client, such as a personal computer, has many resources,
and does not rely on a server for essential functions.