A brief (6 minutes to read) history of MS-DOS:

First released on August 12, 1981, MS-DOS became the foundation for business computing for almost two decades. MS-DOS stood for Microsoft Disk Operating System and was often referred to simply as “DOS”. It is the software that helped build Microsoft, becoming the foundation Microsoft built the Windows operating system on. It went through 8 (and a half-ish) major revisions, with the final version being shipped with Windows ME in September, 2000.