On this day in 1980 Microsoft formally signed a contract with IBM to create an operating system for the then in-development IBM PC. The operating system was based on an existing OS created by Seattle Computer Products. It was originally released with the IBM PC as IBM-PC DOS, but is now famously known as MS-DOS. Microsoft made it so that they acquired and solely developed the operating system, and would be able to sell it to other companies under the name MS-DOS. Because of these actions, MS-DOS became the dominant operating system of the time, and turned Microsoft into the dominant technology company of the PC era.