Sixth Edition Unix, also called Version 6 Unix or just V6, was the first version of the

Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...

to see wide release outside

Bell Labs Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company owned by mult ...

. It was released in May 1975 and, like its direct predecessor, targeted the DEC

PDP-11 The PDP-11 is a series of 16-bit minicomputers sold by Digital Equipment Corporation (DEC) from 1970 into the 1990s, one of a set of products in the Programmed Data Processor (PDP) series. In total, around 600,000 PDP-11s of all models were so ...

family of

minicomputer A minicomputer, or colloquially mini, is a class of smaller general purpose computers that developed in the mid-1960s and sold at a much lower price than mainframe and mid-size computers from IBM and its direct competitors. In a 1970 survey, ...

s. It was superseded by

Version 7 Unix Seventh Edition Unix, also called Version 7 Unix, Version 7 or just V7, was an important early release of the Unix operating system. V7, released in 1979, was the last Bell Laboratories release to see widespread distribution before the commercia ...

in 1978/1979, although V6 systems remained in regular operation until at least 1985.

AT&T Corporation AT&T Corporation, originally the American Telephone and Telegraph Company, is the subsidiary of AT&T Inc. that provides voice, video, data, and Internet telecommunications and professional services to businesses, consumers, and government agen ...

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. An enhanced V6 was the basis of the first ever commercially sold Unix version, 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 Idris may refer to: People * Idris (name), a list of people and fictional characters with the given name or surname * Idris (prophet), Islamic prophet in the Qur'an, traditionally identified with Enoch, an ancestor of Noah in the Bible * Idris G ...

Source code

Version 6 Unix SIMH PDP11 Emulation Source

V6 Unix was released as a distribution including the full

source code In computing, source code, or simply code, is any collection of code, with or without comment (computer programming), comments, written using a human-readable programming language, usually as plain text. The source code of a Computer program, p ...

. 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 The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant u ...

Johns Hopkins University Johns Hopkins University (Johns Hopkins, Hopkins, or JHU) is a private research university in Baltimore, Maryland. Founded in 1876, Johns Hopkins is the oldest research university in the United States and in the western hemisphere. It consiste ...

and the

University of New South Wales The University of New South Wales (UNSW), also known as UNSW Sydney, is a public research university based in Sydney, New South Wales, Australia. It is one of the founding members of Group of Eight, a coalition of Australian research-intensiv ...

(UNSW). UC Berkeley distributed a set of add-on programs called the First Berkeley Software Distribution or 1BSD, which later became a complete operating system distribution. UNSW professor John Lions' famous ''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 Samizdat (russian: самиздат, lit=self-publishing, links=no) was a form of dissident activity across the Eastern Bloc in which individuals reproduced censored and underground makeshift publications, often by hand, and passed the document ...

'' photo-copying. The source code for the original V6 Unix was later made available as

free software Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, ...

under a

BSD License BSD licenses are a family of permissive free software licenses, imposing minimal restrictions on the use and distribution of covered software. This is in contrast to copyleft licenses, which have share-alike requirements. The original BSD li ...

from the SCO Group.

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, thus proving the portability of Unix and its new systems 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

compiler In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs that ...

. 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 The Wollongong Group (TWG) was one of the firscompaniesto sell commercial software products based on the Unix operating system. It was founded to market a port of Unix Version 6 developed by researchers at the University of Wollongong, Australia (t ...

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. The resulting Portable C Compiler (PCC) was distributed with V7 and many later versions of Unix, and was used to produce the

UNIX/32V UNIX/32V is an early version of the Unix operating system from Bell Laboratories, released in June 1979. 32V was a direct port of the Seventh Edition Unix to the DEC VAX architecture. Overview Before 32V, Unix had primarily run on DEC P ...

port to the VAX.

IBM VM/370

A third Unix portability project was completed at Princeton, NJ in 1976–1977, where the Unix kernel was adapted to run as a guest operating on IBM's VM/370 virtualization environment. 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 A real-time operating system (RTOS) is an operating system (OS) for real-time applications that processes data and events that have critically defined time constraints. An RTOS is distinct from a time-sharing operating system, such as Unix, which ...

UNIX/RT, which merged V6 Unix and the earlier

MERT Mert may refer to: People Given name * Mert (given name), a Turkish masculine given name. Surname * Bahar Mert (born 1975), Turkish volleyball player born in Bulgaria * Mesut Mert (born 1978), Canadian association football player and coach of ...

hypervisor. 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. The

University of Sydney The University of Sydney (USYD), also known as Sydney University, or informally Sydney Uni, is a public university, public research university located in Sydney, Australia. Founded in 1850, it is the oldest university in Australia and is one o ...

released the Australian Unix Share Accounting Method (AUSAM) in November 1979, a V6 variant with improved security and process accounting. In the

Eastern Bloc The Eastern Bloc, also known as the Communist Bloc and the Soviet Bloc, was the group of socialist states of Central and Eastern Europe, East Asia, Southeast Asia, Africa, and Latin America under the influence of the Soviet Union that existed du ...

, clones of V6 Unix appeared for local-built PDP-11 clones ( 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 MIT in 2002 through 2006, and subsequently replaced by a simpler clone called xv6.

References

External links

V6 source code

Wollongong Interdata UNIX source code

Unix V6 Manuals
– Web interface to the V6 manual pages.
Unix V6 documents, e.g. C Reference, and man pages

The First Unix Port
Richard Miller's account of porting Unix to the Interdata 7/32
Unix v6 for PDP-11 online emulator
{{Unix-like Bell Labs Unices Discontinued operating systems Unix history Unix variants Free software operating systems 1975 software