Presentation
See the Wikipedia article on Dos at http://en.wikipedia.org/wiki/MSDOS and LearningDos
MS-DOS stands for MicroSoft DiskOperatingSystem. It was a very early text-based operating system and also known as PC-DOS when purchased (retail) from IBM. Windows 3.1, 95, 98, and ME were all programs that were built around DOS (Note 1). Windows XP and 2000 are completely free-standing programs and do not use DOS at all, though a DOS-like command prompt is still available (Note 2) (and some hope will always be available).
By modern standards, DOS wasn't much of an operating system. It offered no memory protection or multi-tasking. Basically, it was a command interpreter, a program loader and a file system. MS-DOS 1.0 was modeled heavily on CP/M (though not as directly as CP/M-86 from Digital Research). MS-DOS 2.0 added some concepts borrowed from Unix, such as subdirectories, I/O redirection and (clumsy) pipes.
You could almost get a real OS by adding DesqView.
The question remains: Is the Tao in the MsDos?
Certainly DOS wasn't revolutionary, even in its time. At least I can't think of anything that was not implemented (even better) in other systems when DOS originally came out. The Macintosh opened the door to Windows, Minix opened the door to Linux.
Who is the DOS curator nowadays?
Surely Microsoft still owns MS-DOS (though IBM must have rights to PC-DOS as variants are still used in some of their cash registers). They've recently begun asserting intellectual property rights for the FAT file system.
DR-DOS (Digital Research's MS-DOS-compatible product after the marketing failure of CP/M-86) was sold via Novell to Caldera, who made it freely available to end users and cheaply licensable to manufacturers. Caldera spun off this business as Lineo which retained DR-DOS. (Caldera subsequently purchased the Santa Cruz Operation, renamed itself SCO and is now attacking Linux.) DR-DOS is now owned by DeviceLogics (http://www.drdos.com/).
Notes:
See: DosPatterns
CategoryOperatingSystem, CategoryMicrosoft, CategoryOldSoftware