824
OS market share in Top 500 supercomputers
(feddit.org)
From Wikipedia, the free encyclopedia
Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.
Community icon by Alpár-Etele Méder, licensed under CC BY 3.0
There's no reason to believe smaller supercomputers would have significantly different OS's.
At some point you enter the realm of mainframes and servers.
Mainframes almost all run Linux now, the last Unix's are close to EOL.
Servers have about a 75% Linux market share, with the rest mostly running Windows and some BSD.