History:

• Version 11, called X11,  first released by MIT in September 1987, was inspirded by Standfords "W" windowing package.
• Release 5 in August 1991 under control of the X Consortium.
• Although X11 is open source it is not free.
• For Linux there is XFree86 and a vrsion exist for MacOS
• For widows can use Cygwin/XFree86, Cygwin is an unix emulator, and XFree86 has been ported to Cygwin.
• XFree86  version 4 came out in 2000 with openGL support and chnaged the format of the configuration file.
• Home page: www.xfree86.org
• Documentation at www.xfree86.org/support.html
  

Goals of X Windows, a windowing  system:

• Standard - Used by almost all workstation
• Portable - Write once run on many workstation
• Network Based - Windowing application can run on remote machines
• Extendable - new drivers and functionality
  

• Displays and Screens - Users workstation
• Display = Keyborad + pointing device + screen
• Multiple screens - physical or virual monitors
• Multiple pointers
  
• Sever - Client Network Model: draw a picture.
• Clients:
• Applications
• Use Xlib Libaray calls
• sends messages to server
• revieves events from server
  
• Server: user sits at the server.
• Allows multiple clients to acess display
  
• Intermediary between clients
• interpets network messages
  
• Communicate with device driver
• On the display machine => does the actual drawing on the display.
• Does most of the work
• Maintians data structures, such as windows, fonts and graphics context....
  
• X-protocal used to communicate between server and client across the net.  
• This enables distriputed computing. 

• Window Manger (WM):
• A special client, only one for each server
• Controls the general appearence of windows
• Syles of window layouts:
• "titled" - no overlapping window - Siemen's RTL WM
• "real-estate driven" - cursor position depends keyboard input destination - TWM
• "click-to-type" - for detemining keyboard focus
• Other examples:  winman.org - web page of many window managers.
• XWM - 1985 toy included in the release
• TWM/VTWM - orginal tapped window manager.
• FVWM - all time favorite, highly configurable
• Desktop Environment (DE) use Window Managers and offer more applications
• Gnome - requires Gnome aware WM, examples are Sawfish, Enlightment, and IceWM
• KDE - uses KWM
• CDE - commerical on unix, uses dtwm.
• Important files:
• startx -> xinit -> WM or DE, scripts found on /usr/X11R6/bin/
• Important rc files are /etc/X11/XF86Config and /etc/X11/xinit/xinitrc, as a user in the home directory.
• Session Mangers - control the shut down and loading of window environment, typically saving application windows settings and location etc.  
  
• Events:
• User inputs - mouse and keyboads
• may generate side effect like exposing a window
  
• User control of application - princple of HCI => client applications ready anytime for any event.
• Events are placed in a queue
  
• Clients application program must have
• Event loop - typically infinite while loop
• Get/Read event
• Branch to event type - typically a switch statement.
• Extensions - Expands capability, for example new drives, and better drawing
• Shape - extension for non rectangle windows
• XInput - more input 
• PEX, which includes PHIGS and PEXLib, api for 3-d graphics
• there is more
• XWindow System Software Architecture
• XLib - client side
• communicate with the server using XProtocals
• Other applications, such as xterm, xclock, xcalc, xmh
• Clients can also use Toolkits, such as XtToolkit, QTK, GTK and others, to make XLib calls
• Xserver - server side
• interpets XProtocals
• maintian DS 
• Sends and revieve messages from drive and therefore the device.
  

X Window System Software Architecture: