1956 [USA]

Tim Paterson was the creator of the QDOS operating system, which was an adaptation of CP/M (at that time the most common operating system for 8-bit computers) to the 8086 chip from Intel, which was acquired by Microsoft to be used as the operating system for the IBM PC with the name PC DOS, and which would later be widely known as MS-DOS. Microsoft also commissioned him to port the system to MSX computers, creating MSX-DOS.