The first operating system used for real work was GM-NAA I/O, produced in 1956 by General Motors’ Research division for its IBM 704. Most other early operating systems for IBM mainframes were also produced by customers.

Is Unix the first operating system?

Unix distinguishes itself from its predecessors as the first portable operating system: almost the entire operating system is written in the C programming language, which allows Unix to operate on numerous platforms.

Is MS-DOS the first operating system?

Microsoft PC-DOS 1.0, the first official version, was released in August 1981. It was designed to operate on the IBM PC. Microsoft PC-DOS 1.1 was released in May 1982, with support for double-sided disks. MS-DOS 1.25 was released in August 1982.