A Berkeley Odyssey: Ten years of BSD history
by Marshall Kirk McKusick
from the January 1985 issue of Unix Review magazine
Ken Thompson and Dennis Ritchie presented the first UNIX paper at the Symposium on Operating Systems Principles at Purdue University in November, 1973. Professor Bob Fabry was in attendance and immediately became interested in obtaining a copy of the system to experiment with at Berkeley.
At the time, Berkeley had only large mainframe computer systems doing batch processing, so the first order of business was to get a PDP-11/45 suitable for running the then current Version 4 of UNIX.