Unix Version 6

6.828's xv6 is inspired by Unix V6 and by:

Lions' Commentary on UNIX' 6th Edition, John Lions, Peer to Peer Communications; ISBN: 1-57398-013-7; 1st edition (June 14, 2000).
- An on-line version of the Lions commentary, and the source code.
- The v6 source code is also available online through the PDP Unix Preservation Society.

The following are useful to read the original code:

The PDP11/40 Processor Handbook, Digital Equipment Corporation, 1972.
- A PDF (made from scanned images, and not text-searchable)
- A web-based version that is indexed by instruction name.