DOS stands for Disk Operating System, which is a type of operating system that runs from a disk drive rather than a paper-based medium like a punch card. DOS is an acronym for disk operating system, and it is a family of disk-based operating systems for IBM PC compatible computers. The DOS family primarily consists of Microsofts MS-DOS and a rebranded version, IBM PC DOS, both of which were introduced in 1981. DOS is a single-user, single-tasking operating system with basic kernel functions that are non-reentrant: only one program at a time can use them, and DOS itself has no functionality to allow more than one program to execute at a time. DOS provides various functions for programs, like character I/O, file management, memory management, program loading, and termination. MS-DOS was the main operating system for IBM PC compatibles during the 1980s, from which point it was gradually superseded by operating systems offering a graphical user interface (GUI), in various generations of the graphical Microsoft Windows operating system.