MS-DOS is a text-based operating system, meaning that a user works with a keyboard to input data and receives output in plain text. Later, MS-DOS often had programs using a mouse and graphics to make work more simple and quick. (Some people still believe that working without graphics is really more efficient.) It is called a disk operating system because it was originally made to be loaded into a computer's memory with a floppy disk each time the computer is started (booted) up.