I imagine the author's using OpenSIMH (https://opensimh.org) or something similar, so it'd be an emulated CPU running the userlands.
I have a container that runs a 4.3 BSD userland using opensimh; it's not super hard to set up, just takes a bit of patience and willingness to learn how opensimh works.
I have a container that runs a 4.3 BSD userland using opensimh; it's not super hard to set up, just takes a bit of patience and willingness to learn how opensimh works.