UBC is one of the more technically challenging things to retrofit onto BSD, see https://www.usenix.org/legacy/event/usenix2000/freenix/full_papers/silvers/silve

UBC is one of the more technically challenging things to retrofit onto BSD, see https://www.usenix.org/legacy/event/usenix2000/freenix/full_papers/silvers/silvers.pdf https://www.usenix.org/legacy/event/usenix2000/freenix/full_... -- in particular note that it wasn't a universal performance improvement as of that paper. Some long lived UNIX like HP-UX never accomplished it. See http://mcvoy.com/lm/papers/SunOS.vm_arch.pdf http://mcvoy.com/lm/papers/SunOS.vm_arch.pdf and http://mcvoy.com/lm/papers/SunOS.vfs_arch.pdf http://mcvoy.com/lm/papers/SunOS.vfs_arch.pdf