[TUHS] Did System V Really Prevent 5BSD?

[Clem Cole via TUHS]

Right idea, wrong release.  4.1BSD was the “fastvax” update from 4.0BSD and
really was an increment from the previous release. 4.1 was triggered by the
Stanford push to use VMS for performance reasons as the official ARPA
supported OS for the VAX. It was CSRG’s naming of 4.2BSD were things got
strange.  When you look at functionality the changes from 4.1 to 4.2 were
huge [Henry Spencer’s famous line:  “4.2 is just like Unix, only
different.”].

As for why CSRG chose to call it 4.2 over 5.0BSD is a bit lost to time. I
don’t think ATT was in any position to “demand” anything. Being at UCB and
my memory of the time was that the folks at CSRG chose to stay away from
the number 5 because they wanted to be sure their work was clearly
distinguished from ATTs — and while the short lived 3.0BSD release was for
the Vax, most people by then associated the numbering 2xBSD to be PDP-11
and 4xBSD to be Vax.  Only later did CSRG start to add a suffix
(Reno/Tahoe) to distinguish other processors as they branched out.  But
when 4.2BSD was released, CRSG had a DARPA contract to support UNIX on the
VAX [BTW, they did not have the contract for IP/TCP, BBN had that contract
and the stories of the issues this caused had been documented/discussed
here in the past].

Sent from a handheld expect more typos than usual


On Sun, Dec 28, 2025 at 6:08 PM segaloco via TUHS <tuhs at tuhs.org> wrote:

> So the prevailing narrative I've heard is that 4.1BSD was so-named at
> AT&T's demand to avoid confusion with System V.  However, the timeline
> leads me to question this.  4.1BSD is given as having been issued first
> June 1981.  Of the Bell lineage, my 4.1 manual also gives June 1981 as a
> publication date.  5.0 wouldn't release inside AT&T for another year, and
> System V manuals give 1983 (i.e. post-divestiture) publication dates
> (although they went to print before, many have Bell logos on the cover
> still.)
>
> In any case, if System V as a product didn't exist until sometime 1983,
> how did the fear of confusion with this name prevent the naming of 5BSD in
> 1981, two years prior?  Was System V as a future trademark already well
> accepted as a given in 1981?
>
> - Matt G.
>