After Bill Gates found out that IBM was looking for an alternative operating system to the one it had originally planned, he bought the rights to QDOS (Quick and Dirty Operating System) from a small software company. IBM acquired the license from Microsoft and integrated it into the IBM PC as PC-DOS 1.0.
PC-DOS took inspiration from CP/M (the operating system IBM had originally planned) and Unix but was found to be lacking in its execution. It turned out to be a rather poorly programmed operating system, leading Microsoft to completely reprogram it. PC-DOS 2.0 then came to market as the first reasonably functioning operating system.
Since IBM did not have an exclusive license for the operating system, Microsoft could also sell it to other companies. Under the name MS-DOS, it became one of the most popular operating systems of its time. In 1982, over 50 companies had licensing agreements for Microsoft’s disk operating system.
As time went on, DOS users asked more and more of their graphical user interface (GUI). Microsoft fulfilled this wish in 1985 with Windows 1.0, which imitated the GUI developed by Xerox back in the 1970s. Apple also launched with a GUI around this time. Users thus no longer had to type commands to open programs - they could simply click on an icon with their mouse.