The X Window System

1. The X Window System Module 5 X-Windows P.K.K.Thambi

2. X Window System • The X Window system was developed as part of Project Athena at MIT. In 1987, X Version 11 is released. X is now controlled and maintained by the Open Group. • The X Windows System, also referred to as ‘X’ or “X11”, is the standard graphical engine for Unix , Linux and Sun workstations. • It is largely OS and hardware independent, it is network-transparent, and it supports many different desktops. X-Windows P.K.K.Thambi

3. The Graphic User Interface in X • X Window uses a bit-mapped display where each pixel can be manipulated individually. • The entire display is known as the root window, and individual applications are displayed as windows on this root window. • X is started with the startx or xinit commands. • X can also be invoked during system startup X-Windows P.K.K.Thambi

4. X-window Screen X-Windows P.K.K.Thambi

5. Client / Server Architecture • Separate programs that talks together for a specific aim. • Server will be the program that supplies the services and the client is who make the requests. X-Windows P.K.K.Thambi

6. X Window Clients and Servers • Although you can easily use the X Window system to run programs stored on your local computer, you can also run applications over the network • X Window uses a client/server model in which a program can run on one computer but display its output on another • The desktop system from which you run a program is called the X server, the system that hosts and executes the program is called the X client (this is opposite of normal networking) X-Windows P.K.K.Thambi

7. X Protocol • Based on TCP/IP stack • The X Protocol provides a client-server architecture at the application level: • The X client is the processing part of the application and often runs on a remote machine. • The X server is the display and interaction system. X-Windows P.K.K.Thambi

8. X Protocol cont’d The X Protocol is also divided into device dependent and device independent layers. X-Windows P.K.K.Thambi

9. X architecture The client-server nature of the X Protocol allows a single X server to support many clients (applications) on several hosts. X-Windows P.K.K.Thambi

10. Client-Server Window System Could beWindowManager Client Application Programs Application 1 Application 2 Application n Virtualdisplay 1 Virtualdisplay 2 Virtualdisplay n Server Resourceallocator Device-independent abstraction level Device driver Translates abstraction into reality: one per terminal type Window1 Devices Keyboard Mouse Window2 Windown (After Fig 10.2, Dix, Finlay, Abowd and Beale) X-Windows P.K.K.Thambi

11. X Server Design • Device Dependent Layer • It is this layer that is responsible for localizing the X server to the native environment, be it Windows NT or Solaris. • This layer swaps bytes of data from machines with differing byte ordering. Byte ordering (MSB and LSB) is noted in each X request. • This layer hides the architectural differences in hardware and operating systems. • Maintains device driver dependencies for keyboard, mouse and video. X-Windows P.K.K.Thambi

12. X Server The X server therefore: • displays drawing requests on the screen. • replies to information requests. • reports an error in a request. • Manages the keyboard, mouse and display device. • Multiplexes keyboard and mouse input onto the network (or via local IPC) to the respective X clients. (X events) • creates, maps and destroys windows. • writes and draws in windows X-Windows P.K.K.Thambi

13. X Client • sends requests to the server. • receives events from server. • receives errors from the server X-Windows P.K.K.Thambi

14. X Protocol • X client communicate with X server using the X protocol. • Data is exchanged in an asynchronous manner over a two-way communication path that enables transmission of a stream of 8 –bit bytes. • X protocol is the machine language for the X Window system X-Windows P.K.K.Thambi

15. X Protocol messages • Requests – client sends requests to the server (e.g. create window) • Replies – server response to client requests • Events – server forwards events (such as mouse clicks or keyboard entry) to the client • Errors – server reports errors to the client X-Windows P.K.K.Thambi

16. Protocol Messages - Requests Requests • X clients make requests to the X server for a certain action to take place. i.e.: Create Window • To enhance performance, the X client normally does not expect nor wait for a response. The request is typically left to the reliable network layer to deliver. X-Windows P.K.K.Thambi

17. Protocol Messages - Replies Replies • The X Server will respond to certain X client requests that require a reply. As noted, not all requests require a reply. X-Windows P.K.K.Thambi

18. Protocol Messages - Events Events • The X server will forward to the X client an event that the application is expecting. This could include keyboard or mouse input. To minimize network traffic, only expected events are sent to X clients. • X events are 32 bytes X-Windows P.K.K.Thambi

19. Protocol Messages - Errors Errors • The X server will report errors in requests to the X client. Errors are like an event but are handled differently. • X errors are the same size as events to simplify their handling. They are sent to the error handling routine of the X client. X-Windows P.K.K.Thambi

20. Xlib: The Assemble language of X • A set of C library of X window system • Xlib gives you access to the X protocol through more than 300 utility routines. • It is the The Assemble language of X Window System. X-Windows P.K.K.Thambi

21. X Toolkit: The High level language of X • XToolkit Intrinsic (Xt Intrinsic) – an object- oriented approach to implement the basic building blocks called widgets X-Windows P.K.K.Thambi

22. X application X toolkit Xt intrinsic Xlib X protocol Network Interface X protocol X Server Device- dependent Layer User Structure of an X application X-Windows P.K.K.Thambi