Quoting from the Wikipedia article:
MS-DOS (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 and 1990s. 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.