[Info-vax] OS Ancestry

[Arne Vajhøj]

On 5/13/2021 8:21 AM, Bill Gunshannon wrote:
> I have become very curious about the ancestry of VMS.  (I am
> going to look into some others, but for VMS I do have this
> outlet for information!)
> 
> Both Primos and Unix came from people recently working on
> Multics.  Primos went in the same direction as Multics while
> Unix appeared to go in a very different direction.
> 
> VMS is more similar to Primos than Unix.  I have seen it said
> that RSX-11 was the immediate parent of VMS.  Was that true?
> Given that, what is the ancestry going back even further?
> Where did VMS actually get its start paradigm-wise?
> 
> Anybody here have any of this information?

The story in Wikipedia is:

https://en.wikipedia.org/wiki/OpenVMS

<quote>
In April 1975, Digital Equipment Corporation embarked on a hardware 
project, code named Star, to design a 32-bit virtual address extension 
to its PDP-11 computer line. A companion software project, code named 
Starlet, was started in June 1975 to develop a totally new operating 
system, based on RSX-11M, for the Star family of processors. These two 
projects were tightly integrated from the beginning. Gordon Bell was the 
VP lead on the VAX hardware and its architecture. Roger Gourd was the 
project lead for the Starlet program, with software engineers Dave 
Cutler (who would later lead development of Microsoft's Windows NT), 
Dick Hustvedt, and Peter Lipman acting as the technical project leaders, 
each having responsibility for a different area of the operating system. 
The Star and Starlet projects culminated in the VAX-11/780 computer and 
the VAX/VMS operating system. The Starlet name survived in VMS as a name 
of several of the main system libraries, including STARLET.OLB and 
STARLET.MLB.
</quote>

https://en.wikipedia.org/wiki/RSX-11

<quote>
RSX-11 is a discontinued family of multi-user real-time operating 
systems for PDP-11 computers created by Digital Equipment Corporation. 
In widespread use through the late 1970s and early 1980s, RSX-11 was 
influential in the development of later operating systems such as VMS 
and Windows NT.
...
RSX-11 began as a port to the PDP-11 architecture of the earlier RSX-15 
operating system for the PDP-15 minicomputer, first released in 1971. 
The main architect for RSX-15 (later renamed XVM/RSX) was Dennis “Dan” 
Brevik.
...
The porting effort first produced small paper tape based real-time 
executives (RSX-11A, RSX-11C) which later gained limited support for 
disks (RSX-11B). RSX-11B then evolved into the fully fledged RSX-11D 
disk-based operating system, which first appeared on the PDP-11/40 and 
PDP-11/45 in early 1973. The project leader for RSX-11D up to version 4 
was Henry Krejci. While RSX-11D was being completed, Digital set out to 
adapt it for a small memory footprint giving birth to RSX-11M, first 
released in 1973. From 1971 to 1976 the RSX-11M project was spearheaded 
by noted operating system designer Dave Cutler, then at his first 
project. Principles first tried in RSX-11M appear also in later designs 
led by Cutler, DEC's VMS and Microsoft's Windows NT.
</quote>

https://en.wikipedia.org/wiki/PDP-15#RSX-15

<quote>
RSX-15 was released by DEC in 1971. The main architect for RSX-15 (later 
renamed XVM/RSX) was Dennis "Dan" Brevik.

Once XVM/RSX was released, DEC facilitated that "a PDP-15 can be 
field-upgraded to XVM" but it required "the addition of the XM15 memory 
processor."

The RSX-11 operating system began as a port of RSX-15 to the PDP-11, 
although it later diverged significantly in terms of design and 
functionality.
</quote>

All before my time.

But I do remember that VAX and VMS VAX had some PDP-11 and RSX-11
compatibility mode features.

Arne