McKernel

Not a replacement for Linux but a second kernel running beside it on the same node. RIKEN's IHK framework splits a compute node's cores between an ordinary Linux kernel, which handles system daemons, device drivers and anything non-HPC, and McKernel, a minimal kernel that executes the same binaries as Linux with far simpler memory management and none of the scheduling jitter a general-purpose kernel introduces under tight synchronization. RIKEN's own Fugaku system-software page lists the OS as "Red Hat Enterprise Linux 8, McKernel" as a pair rather than an either/or choice, and Jack Dongarra's independent University of Tennessee technical report on Fugaku states it directly: "The operating system is Red Hat Enterprise Linux 8 & McKernel (light-weight multi kernel operating system)." The technology predates Fugaku, first demonstrated at production scale on the University of Tsukuba/Tokyo's Oakforest-PACS system in 2016, where it measured up to 3.5x over plain Linux on strong-scaled conjugate-gradient workloads.