"MS-DOS (pronounced /ˌɛmɛsˈdɒs/, em-es-dos; short for MicroSoft Disk Operating System) is an operating system for x86-based personal computers, which was purchased by Microsoft. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for personal computers during the 1980s up to mid 1990s. It was preceded by M-DOS (also called MIDAS), designed and copyrighted by Microsoft in 1979. MSDOS was written for the Intel 8086 family of microprocessors, particularly the IBM PC and compatibles. It was gradually replaced on consumer desktop computers by operating systems offering a graphical user interface (GUI), in particular by various generations of the Microsoft Windows operating system. MS-DOS developed out of QDOS (Quick and Dirty Operating System), also known as 86-DOS.
MS-DOS development originally started in 1981, and was first released in 1982 as MS-DOS 1.0. Several versions were released under different names for different hardware. MS-DOS had eight major versions released before Microsoft stopped development in 2000. It was the key product in Microsoft's growth from a programming languages company to a diverse software development firm, providing the company with essential revenue and marketing resources. It was also the underlying basic operating system on which early versions of Windows ran as a GUI."
Source: Wikipedia, "MS-DOS", available under the CC-BY-SA License.