In order to perfprm the actions requested by the cp users, an operating system must be able to communicate with those users, the portion of an operating sutem that handles this communication is offer called the shell modern shells perform this task by means of a graphical user interface in which objects to be manipulated such as files and programs , are represented pictorially on the monitor screen as icons there ystems allow users to issue commands to the operating system by pointing to these icons by means of a mouse and oressing a button on the mouse older shells communicate with users through textual messasges using a keyboard and monitore screen

although an poerating systems shell plays an important role in establishing a machines functionality this shell is merely an interface betwwen a user and the real heart of the operating system this distinction between the shell and internal parts pf the operating system is emphasized by the fact that some operating systems allow a user to select among different shells to obtain the most compatible interface fotr that  particular user, users of Unix operrating system for example can selecct among a variety of shells including the bourne shell the C shell and the korn shell

an important component within today gui shells is the window manager which allocates blocks of space on the screen called windows and keeps track of which application is associated with each window when an applcation wants to disloay sonething on screen it notifies the window manager and the window manger places the desired image in the window assigned to the application in turn , when a mouse button is clicked it is the window manager that computes the mouse location on the screen and notifies the apprpriate application of the mouse action