What does VERSION 7 stand for? 

Version 7

The first widely distributed version of Unix, released unsupported by Bell Labs in 1978. The term is used adjectivally to describe Unix features and programs that date from that release, and are thus guaranteed to be present and portable in all Unix versions (this was the standard gauge of portability before the POSIX and IEEE 1003 standards). Note that this usage does not derive from the release being the “seventh version of Unix”; research Unix at Bell Labs has traditionally been numbered according to the edition of the associated documentation. Indeed, only the widely-distributed Sixth and Seventh Editions are widely known as V[67]; the OS that might today be known as ‘V10’ is instead known in full as “Tenth Edition Research Unix” or just “Tenth Edition” for short. For this reason, “V7” is often read by cognoscenti as “Seventh Edition”. See BSD, Unix. Some old-timers impatient with commercialization and kernel bloat still maintain that V7 was the Last True Unix.

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