The Graphics Device Interface (GDI, sometimes called Graphical Device Interface) is one of the three core components or "subsystems", together with the kernel and the user (window manager), of Microsoft Windows.
A graphics device interface is a subsystem that most operating systems use for representing graphical objects and transmitting them to output devices such as monitors and printers. In most cases, the graphics device interface is only able to draw 2D graphics and simple 3D graphics, in order to make use of more advanced graphics and keep performance, an API such as Direct X or Open GL needs to be installed.