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X client
Each X application, such as XTerm or Firefox, is a "client". A client sends messages to the server such as "Please draw a window at these coordinates", and the server sends back messages such as "The user just clicked on the OK button".
In a home or small office environment, the X server and the X clients commonly run on the same computer. It is also possible to run the X server on a less powerful computer and to run the X applications on a more powerful system. In this scenario, the communication between the X client and server takes place over the network.
window manager
X does not dictate what windows should look like on-screen, how to move them around with the mouse, which keystrokes should be used to move between windows, what the title bars on each window should look like, whether or not they have close buttons on them, and so on. Instead, X delegates this responsibility to a separate window manager application. There are http://www.xwinman.org/[dozens of window managers] available. Each window manager provides a different look and feel: some support virtual desktops, some allow customized keystrokes to manage the desktop, some have a "Start" button, and some are themeable, allowing a complete change of the desktop's look-and-feel. Window managers are available in the [.filename]#x11-wm# category of the Ports Collection.
Each window manager uses a different configuration mechanism. Some expect configuration file written by hand while others provide graphical tools for most configuration tasks.
desktop environment
KDE and GNOME are considered to be desktop environments as they include an entire suite of applications for performing common desktop tasks. These may include office suites, web browsers, and games.
focus policy
The window manager is responsible for the mouse focus policy. This policy provides some means for choosing which window is actively receiving keystrokes and it should also visibly indicate which window is currently active.
One focus policy is called "click-to-focus". In this model, a window becomes active upon receiving a mouse click. In the "focus-follows-mouse" policy, the window that is under the mouse pointer has focus and the focus is changed by pointing at another window. If the mouse is over the root window, then this window is focused. In the "sloppy-focus" model, if the mouse is moved over the root window, the most recently used window still has the focus. With sloppy-focus, focus is only changed when the cursor enters a new window, and not when exiting the current window. In the "click-to-focus" policy, the active window is selected by mouse click. The window may then be raised and appear in front of all other windows. All keystrokes will now be directed to this window, even if the cursor is moved to another window.
Different window managers support different focus models. All of them support click-to-focus, and the majority of them also support other policies. Consult the documentation for the window manager to determine which focus models are available.
widgets
Widget is a term for all of the items in the user interface that can be clicked or manipulated in some way. This includes buttons, check boxes, radio buttons, icons, and lists. A widget toolkit is a set of widgets used to create graphical applications. There are several popular widget toolkits, including Qt, used by KDE, and GTK+, used by GNOME. As a result, applications will have a different look and feel, depending upon which widget toolkit was used to create the application.
Installing Xorg
On FreeBSD, Xorg can be installed as a package or port.
The binary package can be installed quickly but with fewer options for customization:
# pkg install xorg
To build and install from the Ports Collection:
# cd /usr/ports/x11/xorg
# make install clean