Microsoft Disk Operating System (MS-DOS) is Microsoft’s first OS. Commissioned by IBM, Microsoft bought and modified QDOS for use on IBM’s range of personal computers, or “PCs”.
It soon became the most popular flavor of DOS and remained so for years, however due to its not so user-friendly text-based command-line nature and architecture limitations, it was eventually replaced for general use by Microsoft Windows (and other graphical OSes).
MS-DOS continues to be used for special-purpose uses such as flashing BIOSes and altering disk partitions, as well as for fun by aficionados, although other flavors of DOS including free ones which continue to be developed such as Free-DOS have since become more popular.
Windows command line
Do not use this tag for questions about Windows command line programs or scripts.