[TUHS] Did System V Really Prevent 5BSD?

[Warner Losh via TUHS]

On Sun, Dec 28, 2025, 4:34 PM Clem Cole via TUHS <tuhs at tuhs.org> wrote:

> 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.


I'm pretty sure that 4.1 was going to be 5BSD. I've heard this story from
Kirk several times. He has a listing he labeled 4.5BSD. It was between 4BSD
and 5BSD when he wrote 4.5 on the spine. Whatcwe know today as 4.1BSD was
going to be 5BSD. But when it came time to try to do the paperwork, AT&T
Balked and insisted no 5BSD since it would be confused with the forth
coming System V. I don't know the nuts and bolts of the back and forth to
know if this was a really firm request, or if threats were involved.

I've heard this tale from both Kirk and Eric...

Warner

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.
> >
>