What was the first disk operating system developed to operate on a wide range of computer systems?

The first disk operating system developed to operate on a wide range of computer systems is UNIX. UNIX was created in the late 1960s and early 1970s at Bell Labs and is notable for its portability, multitasking capabilities, and multiuser functionalities. Its design allowed it to be adapted for use on various hardware platforms, making it a significant and influential operating system in the world of computing.

UNIX’s architecture paved the way for many subsequent operating systems and has inspired numerous derivatives and adaptations over the decades, which contributed to its wide-ranging acceptance and use across diverse computing environments. Hence, its design philosophy and capabilities make it the correct choice, showcasing its importance in the development of operating systems for a variety of computer systems.

The other options, while significant in their own rights, do not align with the criteria of being the first disk operating system applicable to a wide range of systems.