What was the first operating system for IBM's Personal Computer (PC)?

Explanation

The IBM task force assembled to develop the PC decided that critical components of the machine, including the operating system, would come from outside vendors. This radical break from company tradition of in-house development was one of the key decisions that made the IBM PC an industry standard. At that time private company Microsoft, founded five years before by Bill Gates, was eventually selected for the operating system.

IBM wanted Microsoft to retain ownership of whatever software it developed, and wanted nothing to do with helping Microsoft, other than making suggestions from afar. According to task force member Jack Sams,