The User Interface
# Most modern operating systems employ a graphical user interface (GUI) with which users control the system by pointing and clicking graphical objects on the screen. A GUI is based on the desktop Icons, windows menus, dialog boxes, and other graphical objects appear on the desktop for the user to manipulate.
# Applications designed to run under a specific operating system use the same interface elements, so users can see a familiar interface no matter what programs they are using. Some older operating systems, such as DOS and UNIX, use command-line interfaces. which the user controls by typing commands at a prompt.