Final answer:
The multiuser OS developed in the 1970s, used on servers and specialized workstations, is Unix (option D). It became commercialized but was later challenged by the cost-effective and customizable Linux, which is now widely used in servers and supercomputers.
Step-by-step explanation:
The operating system fitting the description of a multiuser OS developed in the 1970s, primarily used on servers and specialized workstations, is Unix (d). It was developed by researchers at AT&T Bell Labs and the University of California, Berkeley. Despite starting as a more open system, Unix became commercialized over time, with different organizations releasing proprietary versions that only ran on their hardware.
One notable shift came when Linus Torvalds, frustrated with the high cost of UNIX, developed the Linux kernel, which was not only free but allowed customizable configurations to meet different needs. This led to a variety of distributions and purposes, including use in the top-500 supercomputers and challenging expensive proprietary systems like IRIX and Microsoft NT. Linux played a significant role in the increased accessibility and proliferation of affordable computing power.
Hence, the answer is option d.