Graphical User Interfaces

Typically, with a graphical user interface, the display screen is shared between various tasks. Each task usually has its own region of the screen, known as a window. By selecting different windows, usually by moving the mouse pointer, a user can interact with different tasks, which may be operating concurrently. Furthermore, a user can move and resize windows to alter their layout on the display screen. The manipulation of windows on the display screen, known as window management, is provided by the window manager.

Programmers are presented with a more challenging task in order to produce an application with a graphical user interface. Instead of merely printing prompts to a user and reading character input from a keyboard, the programs have to draw windows, menus, scroll bars and buttons etc, and handle mouse tracking and mouse button clicks and so forth. However, to relieve the burden of the application programmer, most graphical user interface development systems supply a set of software building blocks to handle some of these more complex tasks. These software building blocks are pieces of program code, written by someone else. It is the programmer's task to assemble them in the required, appropriate manner.

As this kind of user interface is based around the concept of a window, the terms window system or windowing system are often used.