The following sections detail important software releases included in the Unix history repository. The level-2 headings mostly correspond to tag or branch names.

The PDP-7 Unix (sometime in mid 1970) is the earliest available version of Unix. It consists of a kernel and user commands, all written in PDP-7 assembly code. It was recovered by scanning assembly language listings of the system's source code; see https://github.com/DoctorWkt/pdp7-unix.

The 1st Edition (November 3, 1971) contains only the kernel; the 60 user commands that came with it are no longer available. Even the kernel, written in PDP-11 assembly language, has not survived in electronic form. It was derived from a group effort that took a scanned June 1972 280-page printout of 1st Edition UNIX source code and documentation, and restored it to an incomplete but running system.

The 2nd Edition (June 12, 1972) source code has only survived in the form of fragments. These were manually restored by Warren Toomey, who pieced together data from a subset of a disk dump’s DECtapes, that were extracted by Dennis Ritchie. The fragments comprise the source code for some of the system’s utilities. The file metadata appears to have been lost. Consequently the file names are guesses, and the timestamps are based on those of the corresponding binary files. This edition’s manual survives as a printed document. In addition to the surviving fragments the repository contains the last C compiler used on the PDP-11/20 and the corresponding C library.

The 3rd Edition (February 1973) contains part of the C compiler (just before it started using structures in its own source code) and the manual pages.

The 4th Edition (November 1973) contains the Unix kernel and the source markup of the manual pages. The kernel predates the actual edition by a few months. It consists of 7609 lines of which just 768 are written in PDP-11 assembly and the rest are written in C. This was the first Unix version to support pipes. However, the C kernel found here had not yet included the pipe support from the assembly language kernel. The manual pages comprise 18975 lines of troff code.

The 5th Edition (June 1974) is missing the source markup of the manual pages. This edition was officially made available to universities for educational use.

The 6th Edition (May 1975), is the first that appears in the repository in complete form, and the first that became widely available outside Bell Labs through licenses to commercial and government users. It was also the last bearing the names of Thompson and Ritchie on the manuals’ title page. The 6th Edition is the one John Lions used for teaching two operating systems courses at the University of New South Wales in Australia. In 1977 Lions produced a booklet with an indexed 9073-line listing of the entire Unix kernel with an equal amount of commentary explaining its structure. Although this was initially sold by mail order, a year afterwards it was no longer available. Nevertheless, for the next two decades it circulated as multiple-generation samizdat photocopies, until in late 1995 the lawyers of Santa Cruz Operation, Inc. gave permission for its official publication.

The snapshot used is amended to include the source code and vocabulary file of M. D. McIlroy's speak(1) program. This is documented in the provided manual pages, but its source code was lost, until Jonathan Gevaryahu found it in unallocated space of a disk dump tape.

The 7th Edition (January 1979), includes many new influential commands, such as awk, expr, find, lex, lint, m4, make, refer, sed, tar, uucp, and the Bourne shell. It also supports larger file systems and more user accounts. It is the version that was widely ported to other architectures.

Unix 32V (or 32/V) is the port of the 7th Edition Unix to the DEC/VAX architecture. It was created by John Raiser and Tom London, managed by Charlier Roberts, at Bell Labs in Holmdel in 1978. There seem to be two reasons why the port was not implemented by the original team. First, DEC’s refusal to support Unix, favouring VMS instead, and, second, the complexity of the VAX instruction set, which apparently went against the values of the Unix patriarchs. The port took about three months to complete by treating the VAX as a large PDP-11 — keeping the existing swapping mechanism and ignoring the VAX’s hardware paging capability. In the fall of 1978 Bell-32V was sent to the University of California at Berkeley under a “special research agreement”.

The first Berkeley Software Distribution (early 1978) contained the Unix Pascal System the ex line editor, and a number of tools.

The Second Berkeley Software Distribution (May 1979), included the full screen editor vi, the associated terminal capability database and management library termcap, and many more tools, such as the csh shell.

The 3BSD release (late 1979), extended Unix 32V with support for virtual memory and the 2BSD additions.

4BSD (October 1980) was developed by the newly established Computer Systems Research Group (CSRG) working on a contract for the Defense Advanced Research Projects Agency (DARPA). The contract aimed at standardizing at the operating system level through the adoption of Unix the computing environment used by DARPA’s research centers. The release included a 1k block file system, support for VAX-11/750, enhanced email, job control, and reliable signals.

4.1BSD (December 1982) a snapshot of 4.1, probably before 4.1a, included performance improvements and auto-configuration support. This release was named 4.1BSD rather than 5BSD in response to objections by  lawyers who feared the 5BSD name might be confused with ’s commercial Unix System V release. Subsequent BSD releases followed this numbering scheme.

The 4.1a distribution had the initial socket interface with a prerelease of the BBN TCP/IP under it. There was wide distribution of 4.1a.

The 4.1b distribution had the fast filesystem added and a more mature socket interface (notably the listen/accept model added by Sam Leffler). There was very limited distribution of 4.1b.

The 4.1c distribution had the finishing touches on the socket interface and added the rename system call to the filesystem. It also added the reliable signal interface. There was very wide distribution of 4.1c as there was a 9-month delay in the distribution of 4.2BSD while DARPA, BBN, and Berkeley debated whether the prerelease of BBN's TCP/IP should be replaced with BBN's finished version. In the end the TCP/IP was not replaced as it had had so much field testing and improvement by the folks running the BSD releases that it was deemed more performant and reliable. There had been a plan to release 4.1d that would have the new virtual memory (mmap) interface, but the delay in getting out 4.2BSD caused that addition to be delayed for the 4.3BSD release.

4.1c2BSD (April 1983) was the last intermediary release preceding 4.2. It was used by many hardware vendors to start their 4.2BSD porting efforts. It included TCP/IP networking, networking tools (ftp, netstat, rlogin, routed, rsh , rwho, telnet, tftp) from 4.1a, and filesystem improvements, such as symbolic links, from 4.1b. Sadly, 4.1aBSD and 4.1bBSD are not included in the CSRG CD set, which was used for obtaining the BSD snapshots for this work.

4.2BSD (September 1983) was a major release of features tested in 4.1aBSD to 4.1c. Compared to the preceding releases it improved networking support and added new signal facilities and disk quotas.

4.3BSD (June 1986) came with performance improvements, a directory name cache, and the BIND internet domain name system server.

4.3BSD Tahoe (June 1988) split the kernel into machine-dependent and machine-independent parts in order to include support for the CCI Power 6/32 minicomputer (code-named Tahoe). It also included improved TCP algorithms.

4.3BSD Networking Release (November 1988) is a subset of the code that does not include material requiring an  license. It was released to help vendors create standalone networking products, without incurring the  binary license costs. It included the BSD networking kernel code and supporting utilities.

4.3BSD Reno (June 1990) supported virtual file system implementations through the vnode interface, Hewlett-Packard 9000/300 workstations, and OSI networking. It also incorporated a new virtual memory system adapted from Carnegie-Mellon’s MACH operating system, a Network File System (NFS) implementation done at the University of Guelph, and an automounter daemon. Considerable material in this release was copyrighted by Berkeley with a license allowing the easy redistribution and reuse of those parts.

4.3BSD Networking Release 2 (June 1991) came with (what is now called) an open source reimplementation of almost all important utilities and libraries that used to require an  license. It also included a kernel that had been cleaned from  source code, requiring just six additional files to make a fully-functioning system. This was the version used by Bill Jolitz to create a compiled bootable Unix system for the 386-based PCs.

4.4BSD Lite (June 1994) was released following two years of litigation and settlement talks regarding the alleged use of proprietary  material between a) Unix System Laboratories (USL — a wholly owned subsidiary of  that developed and marketed Unix) and (later) USL’s new owner, Novell and b) Berkeley Software Design Incorporated (BSDI — a developer of commercially supported version of BSD Unix) and the University of California. As a result this release removed three files that were included in the Net/2 release, added USL copyrights to about 70 files, and made minor changes to a few others. With these changes and according to the settlement’s terms USL could not sue third parties basing their code on this release. Consequently, efforts such as  and NetBSD rebased their work on this code base. The release also included additional work done on the system, such as support for the portal filesystem.

4.4BSD, released at the same time as 4.4BSD Lite, was an “encumbered” version of 4.4-Lite that included the files requiring an  license.

4.4-Lite Release 2 (June 1995) was the last release made by CSRG before the group was disbanded. It included bug fixes and enhancements integrated through funding obtained from the distribution of 4.4.

386/BSD 0.0 (March 1992) is a derivative of the BSD Networking 2 Release developed by Lynne and William Jolitz, who wrote the six missing kernel files targetting the Intel 386 architecture. A description of this system was published as a series of 18 articles in the Dr. Dobb’s Journal.

386/BSD 0.1 (July 1992) is the second release of 386/BSD.

The 386BSD-0.1-patchkit branch (29 June 1992 to 20 June 1993) contains 171 commits associated with patches made to 386BSD 0.1 by a group of volunteers from mid-1992 to mid-1993. Patches contain their changes in Unix “context diff” format, and can therefore be applied automatically to the 386BSD distribution. Each patch is accompanied by a metadata file listing its title, author, description, and prerequisites.

The FreeBSD–release/X tags and branches mark 69 releases derived from the FreeBSD Project. The names of tags and branches to be imported are obtained by excluding from the corresponding  set names matching one of the following patterns: projects/, user/, master, or svn\_head. The  FreeBSD Project started in early 1993 to address difficulties in maintaining 386/BSD through patches and working with its author to secure the future of 386/BSD. The focus of the project was to support the PC architecture appealing to a large, not necessarily highly technically sophisticated audience. For legal reasons associated with the settlement of the USL case, while versions up to 1.1.5.1 were derived from the BSD Networking 2 Release, later ones were derived from the 4.4-Lite Release 2 with 386/BSD additions.