Networked user interface
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The document discusses networked user interfaces and the X Window System. It describes how networked user interfaces allow clients to interact with remote servers through separate counterparts for each service or by offering a user interface to directly access remote services. The X Window System is then presented as an example of the latter approach, where everything is processed and stored at the server. It provides a graphical interface and uses a client/server model, with the desktop as the X server and remote system as the X client, communicating via the X protocol.
Networked user interface
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- 2. Networked User Interface X Window System 27-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. 27-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 Midlewa re 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 Applica tion Indepe ndent protoco l Network 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 27-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. 27-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. 27-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. 27-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. 27-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. 27-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 X kernel Device drivers X protocol Application server Application server User’s Terminal 27-Jan-17 10