Lion’s Commentary and UNIXv6 Source
You can download the full text of the Lion’s Commentary on UNIX here, and the sectioned UNIXv6 source code here.
In addition, you may also find this PDP-11 Handbook a handy reference.
I strongly advise you to print this material out and bring it to class if you do not plan on purchasing the dead-tree version. If you do, it’s available on Amazon for much less than most other course textbooks.