As far as I remember Sunos-4 Kernel became AT&T
Sys5r4 kernel and
made it into Sunos5 which became Solaris.
Nope, Sun got SVR4 dumped on them and then we moved some of the stuff
from SunOS over. But a lot, most of it, got dropped. They are entirely
different kernels.
Don't get me wrong, there is some good stuff in Solaris, but I never
loved it. I loved the SunOS kernel.