In some operating systems (e.g., version 9 of Mac OS from Apple Computer, Inc.), application programs (e.g., a web browser, a word processing software program, a game software program, or others) can assume that there is at least one frame buffer available for drawing their graphical user interfaces. A frame buffer is typically under control of a graphics controller (display controller), which controls a display device according to the information stored on the frame buffer. For example, a typical frame buffer is on the video memory on a graphics card. It is understood that drawing graphical user interfaces on a frame buffer refers to defining display information (e.g., in terms of RGB color values for a color display), typically pixel by pixel, for the display of the graphical user interfaces. The display controller uses the contents of the frame buffer to generate control signals for refreshing the screen of a display device (e.g., a Cathode Ray Tube (CRT) monitor, or a Liquid Crystal Display (LCD) panel).
Some computers may not have a graphics controller and a display device. During the start up time of such a computer that has no graphics controllers, the operating system allocates a virtual frame buffer, using a portion of the system memory of the computer, to provide a place for the application programs to draw their user interfaces. The virtual frame buffer is not associated with or controlled by a particular graphics controller. The virtual frame buffer allows the application programs to generate the display information about their graphical user interfaces properly, even when the computer does not have directly attached graphics controllers and display devices. The content of the virtual frame buffer is not used for the generation of control signals for a display device that is directly attached to this computer.