In 1972-1973 the system was rewritten in the programming language C, an unusual step that was visionary: due to this decision, Unix was the first widely-used operating system that could switch from and outlive its original hardware.

What is the first operating system?

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.

What came first Unix or C?

The relationship between the two is simple; Unix is the first operating system that is implemented with a high-level C programming language, got its fame and power from Unix. Of course, our statement about C being a high-level programming language is not true in today’s world.