Microsoft Windows 95 was intended to integrate Microsoft's formerly separate MS-DOS and Windows products and includes an enhanced version of DOS, often referred to as MS-DOS 7.0. It features significant improvements over its predecessor, Windows 3.1, most visibly the graphical user interface (GUI) whose basic format and structure is still used in later versions. There were also large changes made to the underlying workings, including support for 255-character mixed-case long filenames and preemptively multitasked protected-mode 32-bit applications. Whereas its predecessors are optional "operating environments" requiring the MS-DOS operating system (usually available separately), Windows 95 is a consolidated operating system, which was a significant marketing change.