Released in 1992, this end-point of historical UNIX development on PDP-11's uses almost all features (22 bit addressing, separate I/D space, 3 processor modes) to squeeze a full UNIX with most of the 4.3 BSD features into a 16 bit machine. This operating system can be freely used under the Caldera license and is therefore the prime operating system for the w11 project.

2.11BSD Patches

When bringing up 2.11BSD in the w11a CPU two loose ends in the kernel showed up and were fixed with a patch

2.11BSD Patch Archive Mirror

The master archive of all published 2.11BSD patches is maintained by Steven Schultz on


A mirror, which allows direct access to each individual patch, is provided as part of this project under


2.11BSD Source Code Viewer

The work on the patches mentioned above required a lot of detail studies of the 2.11BSD source code, so it was natural to look for fully htmlized and cross-references source code view. Since none of the available tooks covered the requirements a new tool was was written. For more info see

2.11BSD System Images

A number of ready to use 2.11BSD system images are provided for usage on w11a or on simh in a configuration equivalent to a w11a. Details are provided in the w11 project, section OS Kits.