Ancient UNIX

Ancient UNIX is any early release of the Unix code base prior to Unix System III, particularly the Research Unix releases prior to and including Version 7 (the base for UNIX/32V as well as later developments of AT&T Unix).

Version 5 Unix for the PDP-11, running on SIMH

Version 6 Unix for the PDP-11, running in SIMH

Version 7 Unix for the PDP-11, running in SIMH

After the publication of the Lions' book, work was undertaken to release earlier versions of the codebase. SCO first released the code under a limited educational license.^{[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]

• Research Unix: (early versions only)
  • Version 1 Unix
  • Version 2 Unix
  • Version 3 Unix
  • Version 4 Unix
  • Version 5 Unix
  • Version 6 Unix
  • Version 7 Unix
    • UNIX/32V

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.^[3] Version 6 Unix provides the basis for the MIT xv6 teaching system, which is an update of that version to ANSI C and the x86 or RISC-V platform.

The BSD vi text editor is based on code from the ed line editor in those early Unixes. Therefore, "traditional" vi could not be distributed freely, and various work-alikes (such as nvi) were created. Now that the original code is no longer encumbered, the "traditional" vi has been adapted for modern Unix-like operating systems.^[4]

SCO Group, Inc. was previously called Caldera International. 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.^[6][7]

The Unix Heritage Society

The Unix Heritage Society was founded by Warren Toomey.^[8][9] First edition Unix was restored to a usable state by a restoration team from the Unix Heritage Society in 2008. The restoration process started with paper listings of the source code which were in PDP-11 assembly language.^[10][11]