Wikipedia
SUPER-UX
SUPER-UX, sometimes also annotated SuperUx or Super-UX, is the version of the Unix operating system that is used on NEC SX architecture supercomputers. It is a port of System V Release 4.2MP (SVR4.2MP), but includes many features adopted from BSD and Linux, along with some additional proprietary features specific to a supercomputing environment.
SUPER-UX supports the Supercomputer File System (SFS).
The Earth Simulator used ES OS, an operating system based on SUPER-UX.