Wow, that's a been a while. We had one of these for circuit design hooked up to a cad cam graphics terminal (Tektronix iirc).
A new drive got installed and we had to go and rewire some of the option links to get the DMA to work. That was some fun hardware to work on.
I cut my programming teeth writing apps to run on a network of PDP 11/70s running RSTS/E. Fantastic fun and a remarkably flexible set-up despite the lack of virtual memory.
I still remember machine codes for PDP-11 instructions. I used clone of PDP-11 in my school: cheap school computer with two processors and 192KB of both main and video memory (UKNС). Computer has built-in console debugger, so it was lot of fun to plug computer in and start typing programs in machine code, explore registers, co-processor memory, alter various tables, like font table to draw sprites instead of letters, etc. :-)