Release Date: April, 1974
Released By: UNIX Support Group
Source Code: None Available
Documentation: UNIX Operating System Generic Program Issue 1 describes the files comprising the first Issue of USG Program Generic, which is a revision of USG Release 2.0. This source structure is further described in another report, and the boot process is also described, all in the USG Library. Finally, a sysgen from prior to the source code reorganization survives, demonstrating the prior structure matched Research.
USG UNIX Release 2.0 is the second official release from the UNIX Support Group. Released in April, 1974, it was largely a standard V4 UNIX system with a few extra commands only found in the “user programs” section VI of the manual. This would be the last release to rely on this numbering scheme, with a later revision of 2.x transitioning to the UNIX Program Generic line. As part of this, the source code was rearranged.
This version appears to be comparable to Fourth Edition Unix, albeit retaining some components from earlier Research versions and incorporating some new features that would show up in later systems of other branches.
See Shamim Sharifuddin Pirzada's A Statistical Examination of The Evolution of the UNIX System for more information about the history of USG UNIX.