Linux: It's known. Supercomputers run with this operating system. In the last contest Top500 supercomputer, which took place in June of 2017, 498 from 500 supercomputers operated Linux. The other two used Unix as a functional one.
These were two IBM POWER Chinese AIX-run computers located at the bottom of the list. The machines were found at 493 and 494, while from Top500 held in November 2016, these supercomputers fell over 100 positions.
At this rate, Tux's operating system will have the dominant position in the next Top500 contest every two years.
When the first supercomputer list was created by Top500 in June of 1993, Linux was more like a game than a serious one and had not adopted Tux as his mascot yet.
From 1998, which first appeared on Top500, Linux dominated very fast in ultra-modern calculation.
Prior to taking over Linux, Unix was the top supercomputing operating system. From 2003, however, Top500 showed Linux to go beyond Unix, and until 2004, Linux had taken the lead for the better.
According to the report by The Linux Foundation, the rise of Linux in 20's year of Top500.org Supercomputer contests with advances in computing performance is due to two reasons.
Most of the top supercomputers in the world are ultra-scaled research machines built for specialized tasks. Each supercomputer is a standalone project with unique features and much increased optimization requirements. Thus, it is not accessible to develop a customized operating system for each system. With Linux, engineering teams can easily modify and optimize the functional because of its open nature with innovative designs that characterize modern supercomputers.
Second and equally important:
"The cost of licensing a custom, self-supporting Linux distribution is the same, whether used on 20 nodes or 20 million nodes."
Thus, "by leveraging the huge open source community of the operating system, the projects had access to free support resources and developers, something that keeps developer costs equal to or below other operating systems."
Thus, supercomputer energy, and too many computers other than Windows-based desktops, will continue to use Linux.