UNIX Sixth Edition
This was one of the more popular research versions to leave Bell Labs.
These are the known platforms to run Unix v6
the PDP-11 was the primary platform which Unix v6 was written on. All other v6's can trace themselves back to this version.
The Interdata 32b was the first port to a 32 bit platform outside of Bell Labs.
v6 Unix is perhaps famous because of the "Lions book". John Lions ( bio: http://en.wikipedia.org/wiki/John_Lions ) wrote up an excellent disection of the unix kernel, and taught it in his OS classes. The book became *the* guide to the unix internals, and was photocopied over & over...