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I don't really have a problem, I was just wondering where I could find some documentation about what exactly X server, Xorg, LightDM and stuff like that does.. I always stumble upon those terms, I know they have something to do regarding the graphics, but I'd like to know more.

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X-Windows is a Unix/Linux Client-Server system. Although usually on the same computer, the Client and Server can be on different computers, unlike Microsoft Windows.

X11 is a network protocol. It encodes things such as graphic primitives, images, pointer motion, and key presses.

X clients are graphical applications like Firefox.

Xorg is an X server. It implements X11 and provides an interface to keyboards, mice, and video cards.

Gnome, KDE, LXDE, and Xfce are desktop environments. They provide libraries and specifications that applications use

When running X-Windows, instead of a console login, the Display Manager i.e. Lightdm starts up. The DM starts the X-server and asks for login credentials and then launches the user's desktop environment.

Hope that helps.

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For background information on applications running on Ubuntu I always find the following resources useful:

For deeper insights or other views on applications that run in different distributions we can also find a lot here:

This list is incomplete, I know.

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This architectural overview is a bit outdated, but still mostly applies:

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Whilst this may theoretically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference. – hhlp Mar 5 '13 at 19:48

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