Use the Source/Unix
"Contrary to popular belief, UNIX is user-friendly. It just happens to be very selective about who it decides to make friends with." - Alexander L. Haiut, year unknown, likely pre-1994
Discuss the Unix timestamp, the changing of platforms with the old Unix, the relation between C and Unix.
Then go on to tell some of the releases key points and where the code split into new operating systems like AIX, Tru64 and the like.