Microsoft MS-DOS

MS-DOS is Microsoft's command line Disk Operating System, originally bought and modified to run on the original IBM PC.

It can be said with a degree of certainty that the original deal Microsoft made with IBM, where MS-DOS was licensed to run on IBM's computers instead of sold outright to them, was the chief enabling factor in Microsoft's rise to its current status as the largest software vendor in the world. IBM's "great folly" with DOS was the assumption that "people pay for the hardware; no one makes money on software."