doc mk
jsteve@localhost:~/rt_bsd4/src/sys/.local/mach2.4$ pwd
/home/jsteve/rt_bsd4/src/sys/.local/mach2.4
jsteve@localhost:~/rt_bsd4/src/sys/.local/mach2.4/mk/conf$ cat vers*
69
5
1
X
So 5.1x edit 69
jsteve@localhost:~/rt_bsd4/src/sys/.local/mach2.4/mk$ more CHANGELOG
HISTORY
17-May-88 David Golub (dbg) at Carnegie-Mellon University
XM21:
David Black completely rewrote the accurate timing code
(which is now implemented on all machines) and the priority
and scheduling algorithms. The system now correctly reports
cpu_usage per thread.
The all file has this before i386 was added.
So it's an older v2 than what is on the CSRG CD, but not as old as the VAX '86 stuff.
It seems to be March 11 1989, although that could be when this was either archived or ported.. I guess they didn't exactly sync to a public kernel tree all that often.