I think I found out the reason...Every X release i.e. X11RX.X has a X server version associated with it. For example, X11R7.5 has X Server version 1.7 and the latest X11R7.6 has X Server version 1.9 [1] which clears the confusion. [1] ttp://en.wikipedia.org/wiki/X_Window_System#Release_history