View source for Version 6 Unix

{{Short description|6th Edition of Research Unix alias UNIX Time-Sharing System}}
{{Infobox OS
| name                   = Version 6 Unix<!-- Name of program or distribution -->
| logo                   = <!-- filename only (no wikilink, no Image:/File:) -->
| logo caption           = 
| logo size              = 
| logo alt               = 
| screenshot             = Version 6 Unix SIMH PDP11 Emulation KEN.png<!-- filename only (no wikilink, no Image:/File:) -->
| caption                = Version 6 [[Unix]] for the [[PDP-11]], running in the [[SIMH]] PDP-11 simulator
| screenshot_size        = 
| screenshot_alt         = 
| collapsible            = 
| version of             = <!-- For articles about releases of operating systems ONLY -->
| developer              = [[AT&T Bell Laboratories]]<!-- Name of main developer or sponsor-->
| family                 = [[Unix]]<!-- "Unix-like" or "Microsoft Windows" -->
| working state          = Historic<!-- "Current", "Discontinued" (operating systems), or "No longer supported" (releases) -->
| source model           = Open source<!-- "Open source", "Closed source", or "Shared source" -->
| released               = {{Start date and age|1975|05}}
| discontinued           = <!-- DON'T use this for articles about releases of operating systems -->
| RTM date               = <!-- {{Start date and age|YYYY|MM|DD|df=yes/no}} ONLY for articles about OS releases -->
| GA date                = <!-- {{Start date and age|YYYY|MM|DD|df=yes/no}} ONLY for articles about OS releases -->
| latest release version = 
| latest release date    = 
| latest preview version = 
| latest preview date    = <!-- {{Start date and age|YYYY|MM|DD|df=yes/no}} -->
| marketing target       = [[Minicomputer]]s
| programmed in          = [[C (programming language)|C]], [[assembly language|assembly]]
| language               = [[English language|English]]<!-- Supported human languages (English, French, Italian, Arabic, ...) -->
| update model           = <!-- APT, Windows Update, etc. -->
| package manager        = <!-- dpkg, rpm, Windows installer, etc. -->
| supported platforms    = [[Digital Equipment Corporation|DEC]] [[PDP-11]]<!-- IA-32, x64, Itanium, ARM, etc. -->
| kernel type            = <!-- Hybrid, Monolithic, Microkernel, Exokernel, Nanokernel, etc. -->
| userland               = 
| ui                     = [[Command-line interface]] ([[Thompson shell]])
| license                = Originally [[Proprietary software|proprietary]] [[commercial software]], now [[free software]] under a [[BSD License]]
| preceded by            = [[Version 5 Unix]]
| succeeded by           = [[Version 7 Unix]]
| website                = <!-- {{URL|www.example.org}} -->
| support status         = <!-- For articles about releases of operating systems ONLY -->
| other articles         = 
| prog_language          = 
}}
'''Sixth Edition Unix''', also called '''Version 6 Unix''' or just '''V6''' is a version of the [[Unix]] [[operating system]] first released in May 1975 and the first version of the [[Unix]] [[operating system]] to see wide release outside [[Bell Labs]]. Like its direct predecessor, the sixth edition targeted the [[Digital Equipment Corporation|DEC]] [[PDP-11]] family of [[minicomputer]]s. It was superseded by [[Version 7 Unix]] in 1978/1979, although V6 systems remained in regular operation until at least 1985.<ref name="quarterman42bsd">{{cite journal|last1=Quarterman|first1=John S.|first2=Abraham|last2=Silberschatz |first3=James L. |last3=Peterson|title=4.2BSD and 4.3BSD as examples of the Unix system|journal=Computing Surveys|date=December 1985|volume=17|issue=4|pages=379–418|doi=10.1145/6041.6043|citeseerx = 10.1.1.117.9743|s2cid=5700897|quote=There are even some Version 6 systems still in regular operation.}}</ref>

[[AT&T Corporation]] licensed [[Version 5 Unix]] to educational institutions only, but licensed Version 6 also to commercial users for $20,000, and it remained the most widely used version into the 1980s.<ref name="fiedler198310">{{cite news | url=https://archive.org/stream/byte-magazine-1983-10/1983_10_BYTE_08-10_UNIX#page/n133/mode/2up | title=The Unix Tutorial / Part 3: Unix in the Microcomputer Marketplace | work=BYTE | date=October 1983 | access-date=30 January 2015 | author=Fiedler, Ryan | pages=132}}</ref> An enhanced V6 was the basis of the first ever commercially sold Unix version, [[Interactive Systems Corporation|INTERACTIVE]]'s IS/1. Bell's own [[PWB/UNIX]] 1.0 was also based on V6, where earlier (unreleased) versions were based on V4 and V5. [[Whitesmiths]] produced and marketed a (binary-compatible) V6 clone under the name [[Idris (operating system)|Idris]].

==Source code==
[[File:Lions Commentary Unix.jpeg|thumb|[[John Lions]]' original books, [[source code]] and commentary]]
[[File:Version 6 Unix SIMH PDP11 Emulation Source.png|thumb|Browsing through ''/usr/source'' on Version 6 [[Unix]], running on [[SIMH]]]]

{{main article|Lions' Commentary on UNIX 6th Edition, with Source Code}}

V6 Unix was released as a distribution including the full [[source code]].  Since source code was available and the license was not explicit enough to forbid it, V6 was taken up as a teaching tool, notably by the [[University of California, Berkeley]], [[Johns Hopkins University]] and the [[University of New South Wales]] (UNSW).

UC Berkeley distributed a set of add-on programs called the [[Berkeley Software Distribution|First Berkeley Software Distribution]] or 1BSD, which later became a complete operating system distribution.

UNSW professor [[John Lions]]' famous [[Lions' Commentary on UNIX 6th Edition, with Source Code|''Commentary on UNIX 6th Edition'']] was an edited selection of the main parts of the kernel as implemented for a Digital PDP-11/40, and was the main source of kernel documentation for many early Unix developers. Due to license restrictions on later Unix versions, the book was mainly distributed by ''[[samizdat]]'' photo-copying.

The source code for the original V6 Unix was later made available as [[free software]] under a [[BSD License]] from the [[SCO Group]].<ref>{{cite web|url=https://www.tuhs.org/Archive/Caldera-license.pdf|title=Letter from Caldera announcing the release of the source to older versions of UNIX as free software|access-date=2023-07-31|archive-date=2009-02-19|archive-url=https://web.archive.org/web/20090219220353/http://www.tuhs.org/Archive/Caldera-license.pdf|url-status=live}}</ref>

==Portability==

===Interdata 7/32===
In 1977, Richard Miller and Ross Nealon, working under the supervision of professor Juris Reinfelds at [[Wollongong University]], completed a port of V6 Unix to the [[Interdata 7/32]],<ref>{{cite web |url=http://www.uow.edu.au/content/groups/public/@web/@inf/@scsse/documents/doc/uow103747.pdf |title=The First Port of UNIX |author=Juris Reinfelds |archive-url=https://web.archive.org/web/20150704030021/http://www.uow.edu.au/content/groups/public/@web/@inf/@scsse/documents/doc/uow103747.pdf |archive-date=2015-07-04 |url-status=live}}</ref><ref>{{cite web |url=http://bitsavers.org/bits/Interdata/32bit/unix/univWollongong_v6/miller.pdf |title=The First Unix Port |author=Richard Miller |archive-url=https://web.archive.org/web/20110815093105/http://www.bitsavers.org/bits/Interdata/32bit/unix/univWollongong_v6/miller.pdf |archive-date=2011-08-15 |url-status=live}}</ref> thus proving the portability of Unix and its new systems programming language [[C (programming language)|C]] in practice. Their "Wollongong Interdata UNIX, Level 6" also included utilities developed at Wollongong, and later releases had features of V7, notably its [[C (programming language)|C]] [[compiler]]. Wollongong Unix was the first ever port to a platform other than the PDP series of computers, proving that portable operating systems were indeed feasible, and that C was the language in which to write them. In 1980, this version was licensed to [[The Wollongong Group]] in Palo Alto that published it as Edition 7.

===Interdata 8/32===
Around the same time, a Bell Labs port to the Interdata 8/32 was completed, but not externally released. The goal of this port was to improve the portability of Unix more generally, as well to produce a portable version of the C compiler.<ref name="unixport">{{cite journal |last1=Johnson |first1=S. C. |author-link1=Stephen C. Johnson |last2=Ritchie |first2=D. M. |author-link2=Dennis Ritchie |title=Portability of C Programs and the UNIX System |journal=Bell System Tech. J. |year=1978 |volume=57 |issue=6 |pages=2021–2048 |url=https://www.bell-labs.com/usr/dmr/www/portpap.pdf |access-date=4 June 2022 |doi=10.1002/j.1538-7305.1978.tb02141.x |s2cid=17510065 |archive-date=18 December 2021 |archive-url=https://web.archive.org/web/20211218212919/https://www.bell-labs.com/usr/dmr/www/portpap.pdf |url-status=live }}</ref> The resulting [[Portable C Compiler]] (PCC) was distributed with V7 and many later versions of Unix, and was used to produce the [[UNIX/32V]] port to the [[VAX]].<ref>{{cite web|author1=Thomas B. London|author2=John F. Reiser|year=1978|url=https://www.bell-labs.com/usr/dmr/www/otherports/32v.pdf|title=A Unix operating system for the DEC VAX-11/780 computer|access-date=2016-07-20|archive-date=2015-06-11|archive-url=https://web.archive.org/web/20150611114652/https://www.bell-labs.com/usr/dmr/www/otherports/32v.pdf|url-status=live}}</ref>

===IBM VM/370===
A third Unix portability project was completed at [[Princeton, New Jersey|Princeton, NJ]] in 1976–1977, where the Unix kernel was adapted to run as a guest operating on IBM's [[VM (operating system)|VM/370]] virtualization environment.<ref name="unixport"/> This version became the nucleus of Amdahl's first internal UNIX offering. (see [[Amdahl UTS]])

==Variants and extensions==
Bell Labs developed several variants of V6, including the stripped-down MINI-UNIX for low-end PDP-11 models, LSI-UNIX or LSX for the [[LSI-11]], and the [[real-time operating system]] UNIX/RT, which merged V6 Unix and the earlier [[Multi-Environment Real-Time|MERT]] hypervisor.<ref>{{cite conference|last1=Bayer|first1=D. L.|last2=Lycklama|first2=H.|title=Proceedings of the fifth symposium on Operating systems principles - SOSP '75 |chapter-url=http://portal.acm.org/citation.cfm?id=806519|chapter=MERT - a multi-environment real-time operating system|conference=Fifth ACM Symposium on Operating Systems Principles|location=Austin, TX|year=1975|pages=33–42 |doi=10.1145/800213.806519|doi-access=free}}</ref>

After AT&T decided the distribution by Bell Labs of a number of pre-V7 bug fixes would constitute support (disallowed by an antitrust settlement) a tape with the patchset was slipped to Lou Katz of [[USENIX]], who distributed them.<ref>{{cite journal|last=Toomey|first=Warren|title=The Strange Birth and Long Life of Unix|url=https://spectrum.ieee.org/the-strange-birth-and-long-life-of-unix|journal=[[IEEE Spectrum]]|date=December 2011|volume=48|issue=12|pages=34–55|publisher=[[IEEE]]|doi=10.1109/MSPEC.2011.6085780|s2cid=29893166|access-date=August 25, 2024|url-access=subscription}}</ref>

The [[University of Sydney]] released the Australian Unix Share Accounting Method (AUSAM) in January 1978, a V6 variant with improved security and process accounting, in addition to the fifty fixes that leaked out of Bell Labs. There were several subsequent releases.

[[Interactive Systems Corporation]] released an enhanced [[PDP-11]] version for office automation called [[Interactive Systems Corporation#Products|IS/1]].<ref name="Oak Ridge">{{cite journal |first=R.D. |last=McCulloch |title=Putting it on the Line |url=https://books.google.com/books?id=oOvMdukBDRwC |journal=Oak Ridge National Laboratory Review |volume=14 |issue=3 |date=Summer 1981 |page=19 |access-date=2023-07-29 |archive-date=2023-07-31 |archive-url=https://web.archive.org/web/20230731175311/https://books.google.com/books?id=oOvMdukBDRwC |url-status=live }}</ref>

In the [[Eastern Bloc]], clones of V6 Unix appeared for local-built PDP-11 clones ([[MNOS (operating system)|MNOS]], later augmented for partial compatibility with BSD Unix) and for the [[Elektronika BK]] personal computer ([[BKUNIX]], based on LSX).

V6 was used for teaching at [[Massachusetts Institute of Technology|MIT]] in 2002 through 2006, and subsequently replaced by a simpler clone called [[xv6]].

==See also==
*[[Ancient UNIX]]
* {{anl|xv6}}

==References==
{{Reflist}}

==External links==
* [http://minnie.tuhs.org/cgi-bin/utree.pl?file=V6 V6 source code]
* [http://minnie.tuhs.org/cgi-bin/utree.pl?file=Interdata732 Wollongong Interdata UNIX source code]
* [http://man.cat-v.org/unix-6th/ Unix V6 Manuals] – Web interface to the V6 manual pages.
* [http://doc.cat-v.org/unix/v6/operating-systems-lecture-notes/v6/ Unix V6 documents, e.g. C Reference, and man pages]
* [http://www.usenix.org/publications/library/proceedings/usenix98/invited_talks/miller.ps The First Unix Port]; Richard Miller's account of porting Unix to the Interdata 7/32
* [http://pdp11.aiju.de/ Unix v6 for PDP-11 online emulator]

{{Bell Unix}}
{{Unix-like}}

[[Category:Bell Labs Unices]]
[[Category:Discontinued operating systems]]
[[Category:Unix history]]
[[Category:Unix variants]]
[[Category:Free software operating systems]]
[[Category:1975 software]]