When trn says that I/O is handled by the FNP, he actually means terminal I/O and communications I/O. Actual disk, tape, and other peripheral I/O is performed by the Input Output Multiplexer (IOM) — yet another hardware component in the DPS8 hardware suite. The CPUs. IOMs, SCUs, and FNPs are emulated by the DPS8M simulator. And yes, the DPS8M simulator supports multiple of these components for a single Multics system.

We should also mention that the PDF documentation has some graphics showing how these components are (physically) connected together at https://dps8m.gitlab.io/dps8m-r3.0.1-archive/R3.0.1/omnibus/... (pages 49 through 52).

If you'd prefer not to have to view the PDF, the images are reproduced here: https://imgur.com/a/x3fy4nO

Yes, I was simplifying a bit :) Those who are interested should take a peek at https://dps8m.gitlab.io/dps8m/Overview/#supported-components to see all the various components that make up the DPS mainframe system.

Here's a brochure about the DPS8/M. [PDF]

https://www.1000bit.it/js/web/viewer.html?file=%2Fad%2Fbro%2...

We have quite a few machines running ITS, LISPM, and other OSs on the chaosnet today. See https://chaosnet.net for details.