I want to learn more about UNIX systems and I think I have a pretty straight forward question. I think I know what X is used for: It gives a standard to applications to present their UI's (among other things).But why then is there a need for Gnome/KDE and how do they relate to X? I thought that they were using X as some sort of interface between the application and the GUI, so the GUI is customize-able while the interface stays the same across applications.Is that true or is Gnome/KDE independent of X? 
Difference between Xorg and Gnome/KDE/Xfce
x11;xorg;gnome;kde;desktop environment