Interlisp was developed at BBN on the PDP-10 under the TENEX operating system. Danny Bobrow had previously been at MIT and worked on MACLISP running on PDP-10s

Interlisp was developed at BBN on the PDP-10 under the TENEX operating system. Danny Bobrow had previously been at MIT and worked on MACLISP running on PDP-10s running the ITS OS. So that mode was and is perfectly normal. When Danny went to PARC they started working on a port of Interlisp to the D machine hardware. The model adopted was that of smalltalk: a hermetic environment running on the bare iron, with everything (drivers, network stack etc) written in lisp. One big difference from the MIT world was that smalltalk and Interlisp were built around working in a world and checkpointing the entire machine state, rather than loading files into a base image. PARC also had a lot of network-only RPC services (mail, filesystem, printing, etc) so each environment had its own implementation of talking to these services, and all its own UX. We’re talking late 70s here, some of it more sophisticated than what you can get today.