zlacker

I'm believe /sbin was introduced/standardized in System V Release 4. It's present in SVR4 (1988) but not in SVR3 (1987). Another candidate is would be some old BSD (check 4.2 or 4.3 (1986) if anyone has a running system).

I'm guessing it was introduced to finally move out all the (mostly system) binaries from /etc, which in ancient Unix from Bell Labs in the 1970s really meant "etc", as in stuff that didn't fit elsewhere rather than system config files, so it contained binaries like init, mount, umount.