What is Microsoft Windows OS?

Microsoft made world first graphical operating system windows, And it is most popular desktop operating system of the world. Microsoft is  a leader of graphical operating system. Before Microsoft Windows there was a world of non GUI (Character based operating system like dos,Unix)OS. Microsoft windows made revolution of GUI. There are many version of Microsoft windows like, windows 95, windows 98, window me,windows NT, windows 2000, windows XP, windows vista, windows 7, windows 8 etc,