| Version 6 Unix | |
|---|---|
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| Developer | AT&T Bell Laboratories |
| Written in | C,assembly |
| OS family | Unix |
| Working state | Historic |
| Source model | Open source |
| Initial release | May 1975; 50 years ago (1975-05) |
| Marketing target | Minicomputers |
| Available in | English |
| Supported platforms | DECPDP-11 |
| Default user interface | Command-line interface (Thompson shell) |
| License | Originallyproprietarycommercial software, nowfree software under aBSD License |
| Preceded by | Version 5 Unix |
| Succeeded by | Version 7 Unix |
Sixth Edition Unix, also calledVersion 6 Unix or justV6 is a version of theUnixoperating system first released in May 1975 and the first version of the Unix operating system to see wide release outsideBell Labs. Like its direct predecessor, the sixth edition targeted theDECPDP-11 family ofminicomputers. It was superseded byVersion 7 Unix in 1978/1979, although V6 systems remained in regular operation until at least 1985.[1]
AT&T Corporation licensedVersion 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.[2] An enhanced V6 was the basis of the first ever commercially sold Unix version,INTERACTIVE's IS/1. Bell's ownPWB/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 nameIdris.
V6 Unix was released as a distribution including the fullsource 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 theUniversity of California, Berkeley,Johns Hopkins University and theUniversity of New South Wales (UNSW).
UC Berkeley distributed a set of add-on programs called theFirst Berkeley Software Distribution or 1BSD, which later became a complete operating system distribution.
UNSW professorJohn Lions' famousCommentary 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 bysamizdat photo-copying.
The source code for the original V6 Unix was later made available asfree software under aBSD License from theSCO Group.[3]
In 1977, Richard Miller and Ross Nealon, working under the supervision of professor Juris Reinfelds atWollongong University, completed a port of V6 Unix to theInterdata 7/32,[4][5] thus proving the portability of Unix and its new systems programming languageC in practice. Their "Wollongong Interdata UNIX, Level 6" also included utilities developed at Wollongong, and later releases had features of V7, notably itsCcompiler. 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 toThe Wollongong Group in Palo Alto that published it as Edition 7.
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.[6] The resultingPortable C Compiler (PCC) was distributed with V7 and many later versions of Unix, and was used to produce theUNIX/32V port to theVAX.[7]
A third Unix portability project was completed atPrinceton, NJ in 1976–1977, where the Unix kernel was adapted to run as a guest operating on IBM'sVM/370 virtualization environment.[6] This version became the nucleus of Amdahl's first internal UNIX offering. (seeAmdahl UTS)
Bell Labs developed several variants of V6, including the stripped-down MINI-UNIX for low-end PDP-11 models, LSI-UNIX or LSX for theLSI-11, and thereal-time operating system UNIX/RT, which merged V6 Unix and the earlierMERT hypervisor.[8]
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 ofUSENIX, who distributed them.[9]
TheUniversity 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 enhancedPDP-11 version for office automation calledIS/1.[10]
In theEastern Bloc, clones of V6 Unix appeared for local-built PDP-11 clones (MNOS, later augmented for partial compatibility with BSD Unix) and for theElektronika BK personal computer (BKUNIX, based on LSX).
V6 was used for teaching atMIT in 2002 through 2006, and subsequently replaced by a simpler clone calledxv6.
There are even some Version 6 systems still in regular operation.
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