Basic X Terms

Basic X Terms
As with most technical environments, X has its own special jargon. You should understand some basic terms. More detailed definitions of these terms can be found in the references listed at theend of this document.Display Servers, Hosts, and Clients
As mentioned in the preceding section, applications do not necessarily run on the terminal where you are working. Your computer terminal is called a display server, and applications are called clients. The computers which actually execute your clients are called hosts (they are also known as compute servers).

As an example, the Owlnet Sun 3/50 workstations act purely as X display servers. In these cases, any clients you start are not executing on your computer. X directs your input to a host and directs output to your display server. On Owlnet, your clients actually execute on one of the Sun SPARCstations named arcadien, barred, boreal, elf, hawk, spotted, and so on.

If the term "client" causes confusion, you can substitute "application" if that makes X concepts easier to understand. Similarly, "terminal" can be substituted for "display server."

Screens and Displays
One common stumbling block arises because an X "screen" and "display" are not equivalent terms. A display corresponds most closely to the video monitor. A single monitor never has more than one display. It is possible for some displays to support more than one screen. When this occurs on a single monitor, moving the cursor past the right or left edge of the monitor will cause the second screen to appear on that monitor instead of the first. It is also possible to have two monitors serve as different screens for the same display, in which case moving the cursor off the right side of one monitor would have it appear on the left side of the other!

For example, one display might use two screens to display a very wide Mercator map of the world. This could be accomplished using one monitor or two. Some machines have a single physical video monitor (and a single display) but that display has two screens: a black-and-white screen and a separate color screen.

Windows and Icons
"Window" is probably a familiar term. A window is an enclosed area (usually a rectangle) that represents a particular client and displays your interaction with that client. Title bars and icons are functions of the Window Manager. For different clients, activity within each window proceeds independently of activity in other windows. Some clients have multiple windows that interact with each other. With the exception of some paginators, windows can be moved and resized without affecting the execution of their clients. Overlapping windows do not affect each other.

One special window is the root window, which forms the background of the display. Inside the root window you can perform window management functions rather than ordinary input and output with a window.

Windows can also be represented by icons. Icons are small rectangular symbols used to keep many clients from cluttering the screen. Generally, you cannot send input to a client's icon. First you must de-iconify the icon to convert the icon into a window; then you may send input to that client. After completing input, you can iconify the window to convert it into an icon. A client will continue to execute when in its iconic form. For example, you can open a window, enter the input to run a program, and iconify the window. At some later time you can de-iconify the icon to view the program's output.

Pointing Devices and Cursors
Usually you employ a pointing device like a mouse in X. The section "Using the Mouse" explains how to use a mouse, graphics tablet, or light pen to perform most window operations. These operations include opening windows, selecting text within windows, moving icons and windows, and viewing menus.

The cursor lets you know where the pointing device is pointing on the screen. The cursor may be an arrow, an `X,' or some other symbol. Depending on the pointing device's target, the mouse buttons may invoke different operations. The cursor symbol usually changes to indicate these changing targets. For example, in the body of most windows the cursor is an I-beam, on the title bar the cursor is an arrow, and on the root window the default cursor is an `X.'

Window Managers
To enable window operations, X runs a client called a window manager. The window manager handles local operations like moving, resizing, and iconifying windows. The window manager handles the appearance and manipulation of windows while X supervises communication between windows, applications, and input/output devices (like the monitor keyboardl).

The window manager is a special client of the X server. It is the only client with the ability to move, resize, map, unmap, iconify, and deiconify windows. The window manager normally has no windows itself, with the exception of the menu windows the user can summon. It is possible to run an X session without using a window manager, but parts of windows hidden under other windows would be inaccessible.

Several different window managers exist, and each user can choose his or her own window manager. However, you can only use one window manager at a time. For example, suppose there are two window managers available: the Tab and Motif Window Managers. Now when you log on, you may use either the Tab or the Motif Window Manager, but not both.

A later section discusses the Tab Window Manager in detail.

Part of customizing X is changing your default window manager behavior to produce a display that suits your own needs. (See the separate Information Systems Document Customizing X for information on altering the default X environment and customizing TWM.) Other window managers include the "Motif Window Manager" (mwm), the "OPEN LOOK Window Manager" (olwm), and the Silicon Graphics Window Manager (4Dwm) used on the SGIs in RAVL and Fondren Library.