Sixth Edition Unix

Sixth Edition Unix, also called Version 6 Unix or just V6, was the first version of the Unix operating system to see wide release outside Bell Labs. It was released in May 1975. 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 and the University of New South Wales (UNSW).

V6 was notable for Lions' Commentary on UNIX 6th Edition, also known as the Lions Book after its author, UNSW professor John Lions. This book 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.

The code has been made available under a BSD License under agreement from the SCO Group; see Ancient UNIX Systems.


Apart from the first BSD (1BSD), several other Unixes were derived from the V6 code base.

IS/1 was INTERACTIVE's enhanced V6, the first ever commercially sold Unix version.

A port of V6 to the Interdata 7/32 was completed by Richard Miller and Ross Nealon at Wollongong University, Australia, during 1976-1977. This project was supervised by professor Juris Reinfelds. The resulting system was called Wollongong Interdata UNIX, Level 6. This distribution also included utilities developed at Wollongong, and later releases had features of V7, notably its 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.

A port of V6 to the Interdata 8/32 was completed within Bell Labs, but this version was never released.

A version of V6 for lower-end PDP-11 systems, such as the 11/10, was available as MINI-UNIX.

PWB/UNIX 1.0 was based on V6 (earlier, internal use-only versions were based on V4 and V5).

UNIX/RT was a real-time operating system, based on V6 and the earlier MERT (Multi-Environment Real-Time Operating System) hypervisor.

LSI-UNIX or LSX was a minimal Unix for the LSI-11 microprocessor variant of the PDP-11. It ran in 40kB of memory, with the kernel occupying only 16kB

AUSAM (Australian Unix Share Accounting Method), released in November 1979, was a V6 variant from the University of Sydney, Australia. Its main improvements were better security and process accounting.

MNOS was V6-based version of Unix, popular on various Soviet and Eastern Bloc PDP-11 clones; over the years it was heavily augmented for partial compatibility with BSD Unix.

BKUNIX, based on LSX is the only version of UNIX, working on Elektronika BK Soviet personal computer.

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