Client Definition

A client is a computer, program or process that makes requests for information from another computer, program or process in a client-server relationship.

The client-server architecture (i.e., network design) divides work between two separate, but linked, applications, referred to as clients and servers. The latter, which typically (but not necessarily) run on remote machines (i.e., computers located elsewhere on the network), handle requests from multiple users, process the data as requested and return the results to the users' computer screens.

The client application typically runs on the local computer (i.e., the computer that is being used directly by the user), helps the user request data from the server and displays the requested data in a user friendly manner.

One of the most familiar client application programs is the web browser, whose main tasks are to request web pages from web servers scattered around the Internet and then convert the HTML (hypertext markup language) and other code returned by the servers into text and images that are useful to the user.

Another common example is e-mail clients, which are application programs, such as Eudora, Evolution, KMail, Pine or Thunderbird, that make possible the sending and receiving of e-mail. One of the earliest clients on the Internet was Telnet, which can allow logging in to remote computers in order to use them for accessing data or for other purposes.

In the X Window System, the dominant system for managing GUIs (graphical user interfaces) on Unix-like operating systems, the meanings of client and server are somewhat reversed. Although a network using the X window system can still involve multiple client machines accessing a single or multiple server machines, each client machine contains an X server and can access remote machines (i.e., servers in the usual sense) that run X clients. An X server is a program that runs on the local machines and handles all access to the graphics hardware and to the single screen, keyboard and mouse. X clients are application programs that display on the X server but which is otherwise independent of that server. In X, any application program that uses the GUI becomes an X client.

Created October 11, 2005. Updated January 19, 2006.
Copyright © 2005 - 2006 The Linux Information Project. All Rights Reserved.