page_title: Version 6 Unix
section_title: Source code
hierarchical_section_title: Version 6 Unix / Source code
caption_attribution_description: English: Version 6 Unix for the PDP-11, running in the SIMH PDP-11 simulator. Browsing through "/usr/source", where the Unix source code is located.
context_page_description: 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 and, like its direct predecessor, targeted the DEC PDP-11 family of minicomputers. It was superseded by Version 7 Unix in 1978/1979, although V6 systems remained in regular operation until at least 1985.
  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. 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 versions were based on V4 and V5. Whitesmiths produced and marketed a V6 clone under the name Idris.
context_section_description: 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 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 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.
caption: Browsing through /usr/source on Version 6 Unix, running on SIMH
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