Ancient UNIX

After the publication of the Lions' book, work was undertaken to release earlier versions of the codebase.

[citation needed] Later, in January 2002, Caldera International (later to become SCO Group and made defunct) relicensed (but has not made available) several versions under the four-clause BSD license, namely:[1][2] As of 2022[update], there has been no widespread use of the code, but it can be used on emulator systems, and Version 5 Unix runs on the Nintendo Game Boy Advance using the SIMH PDP-11 emulator.

Now that the original code is no longer encumbered, the "traditional" vi has been adapted for modern Unix-like operating systems.

As a result of the SCO Group, Inc. v. Novell, Inc. case, Novell, Inc. was found to not have transferred the copyrights of UNIX to SCO Group, Inc.[5] Concerns have been raised regarding the validity of the Caldera license.

The restoration process started with paper listings of the source code which were in PDP-11 assembly language.