Oh, The joys of a shelf full of old computer books.
DEC transitioned MUMPS from the 18-bit line onto the PDP-11s. I think that the majority of Mumps systems were on the 11s and then moved to VAX as it came on the scene. I can find no mention in the PDP-8 books. If MUMPS was moved there it was not a standard DEC product. Likewise, the PDP-10 books don't cover MUMPS. I would assume that it was moved to the 36-bit machines, but have no reference. Does anyone out ther have some record of MUMPS on the PDP-10??
The DEC PDP-11 reference manual set had one volume on software systems for the PDP-11s.
I pulled the 1975 and 1980 versions.
DEC PDP-11 Software Handbook, Copyright 1975
Section II: PDP-11 Operating Systems
Chapter 1: Cassette Programming System CAPS-11
Chapter 2: Foreground/Background RT-11
Chapter 3: Resource Sharing Timesharing System RSTS/E
Chapter 4: Multi-user Database Managemetn System MUMPS-11
Chapter 5: RSX-11
Chapter 6: IAS
The intro to MUMPS describes it as: A small to large sized timesharing system that offers a unique fast access data storage and retrieval system for large database processing.
The MUMPS chapter is 26 pages long with a reasonable amount of reference detail for the time. The database aspect was the unique selling point.
By the 1980 version of the same DEC PDP-11 Software Handbook, MUMPS had moved to Chapter 8: Digital Standard MUMPS.
The intro section describes:
DSM-11 Digital Standard MUMPS operating system for PDP-11 processors.
A small to large sized timesharing system that offers a unique fast-access data storage and retrieval system for large data base processing. Originally designed for medical record management and now available for similar data base applications.
Chapter 8 of the 1980 Software Handbook has a more prose-like description than the reference-manual-like 1975 chapter. The new version has a good description of hospital medical record processing and claims over 500 major hospitals using MUMPS.
So it was under active development and use through the 70s on the PDP-11s.
With that base it is not surprising that MUMPS is still in use.