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2. Networked User Interface X Window System 8-Jan-17 2

3. Networked User Interfaces  A major task of client machines is to provide the means for users to interact with remote servers.  There are roughly two ways in which this interaction can be supported.  For each remote service the client machine will have a separate counterpart that can contact the service over the network.  Example: an agenda running on a user’s PDA that needs to synchronize with a remote, possibly shared agenda.  to provide direct access to remote services by only offering a convenient user interface.  Effectively, this means that the client machine is used only as a terminal with no need for local storag leading to an application-neutral solutions. 8-Jan-17 3

4. Cont’d....  In the case of networked user interfaces,  everything is processed and stored at the server. The following diagram shows that the client/Server communication with Networked user interfaces Applica tion Midlew are Local OS Applicati on Local OS Midlewar e Application Midleware Local OS Applicati on Local OS Midleware Client Machine Server machine Client Machine Server machine Application specific protocol Applic ation Indep enden t protoc ol Network Figure 3.8: (a) A networked application with its own protocol. (b ) A general solution to allow access to remote applications. Available on the reference book, page 103-104 8-Jan-17 4

5. Cont’d...  In the case of networked user interfaces  everything is processed and stored at the server  Example: the X window system  It is one of the oldest and still widely used networked user interface.  X window system  is a GUI that runs on Linux and many UNIX operating systems  Like windows and macintosh operating system,  It provides an easy-to-use  Graphical method of operating the computer. 8-Jan-17 5

6. Cont’d...  Programmers may also develop applications that run on the X Window system and support GUI components such as  Windows, dialog boxes, buttons, and pull-down menus  Although you can easly use the X Window system to run programs stored on your local computer,  you can also run applications over a network  X Window uses Client/Server model where a program can run on one computer but display its output on another.  In X Window netwok terminology,  the desktop system that the user runs a program from is called X server  The system that hosts \and executes the program is clled the X client. 8-Jan-17 6

7. Cont’d...  In X window jargon, the temrs cleint and server mean the oposite  The terms are reversed because the X Window server (on the desktop) performs operations requested by the client (on the host system).  The X Window System, generally referred to simply as X, is used to control bit-mapped terminals,  which include a monitor, keyboard, and a pointing device such as a mouse.  In a sense, X can be viewed as that part of an operating system that controls the terminal.  The heart of the system is formed by what we shall call the X kernel. 8-Jan-17 7

8. Cont’d...  The X kernel contains all the terminal-specific device drivers, and as such, is generally highly hardware dependent.  The X kernel offers a relatively low-level interface for controlling the screen, but also for capturing events from the keyboard and mouse.  This interface is made available to applications as a library called Xlib.  The interesting aspect of X is that the X kernel and the X applications need not necessarily reside on the same machine. 8-Jan-17 8

9. Cont’d...  In particular, X provides the X protocol, which is an application-level communication protocol by which an instance of Xlib can exchange data and events with the X kernel.  For example, Xlib can send requests to the X kernel for creating or killing a window, setting colors, and defining the type of cursor to display, among many other requests.  In turn, the X kernel will react to local events such as keyboard and mouse input by sending event packets back to Xlib. 8-Jan-17 9

10. Cont’d... Figure 3.9: The basic organization of the X Window System (Available on reference book on page 104-105)  Several applications can communicate at the same time with the X kernel.  There is one specific application that is given special rights, known as the window manage.  For example, the window manager can prescribe how each window is decorated with extra buttons, how windows are to be placed on the display, and so.  Other applications will have to adhere to these rules. Window manager Xlib Local OS Application Xlib Local OS Xlib interfa ce X kernel Device drivers X protocol Application server User’s Terminal 8-Jan-17 10

11. THE E ND. Thank You!!! 8-Jan-17 11