Graphical User Interface
(GUI) The use of pictures rather than just words to represent the input and output of a program. A program with a GUI runs under some windowing system (e.g. The X Window System, MacOS, Microsoft Windows, Acorn RISC OS, NEXTSTEP). The program displays certain icons, buttons, dialogue boxes, etc. in its windows on the screen and the user controls it mainly by moving a pointer on the screen (typically controlled by a mouse) and selecting certain objects by pressing buttons on the mouse while the pointer is pointing at them. This contrasts with a command line interface where communication is by exchange of strings of text.
Windowing systems started with the first real-time graphic display systems for computers, namely the SAGE Project [Dates?] and Ivan Sutherland's Sketchpad (1963). Douglas Engelbart's Augmentation of Human Intellect project at SRI in the 1960s developed the On-Line System, which incorporated a mouse-driven cursor and multiple windows. Several people from Engelbart's project went to Xerox PARC in the early 1970s, most importantly his senior engineer, Bill English. The Xerox PARC team established the WIMP concept, which appeared commercially in the Xerox 8010 (Star) system in 1981.
Beginning in 1980(?), led by Jef Raskin, the Macintosh team at Apple Computer (which included former members of the Xerox PARC group) continued to develop such ideas in the first commercially successful product to use a GUI, the Apple Macintosh, released in January 1984. In 2001 Apple introduced Mac OS X.
Microsoft modeled the first version of Windows, released in 1985, on Mac OS. Windows was a GUI for MS-DOS that had been shipped with IBM PC and compatible computers since 1981. Apple sued Microsoft over infringement of the look-and-feel of the MacOS. The court case ran for many years.