I remember reading an old paper on some funky experimentat user-interface that used a pair of PDP-11s (possibly, might have been event older) essentially wired

I remember reading an old paper on some funky experimentat user-interface that used a pair of PDP-11s (possibly, might have been event older) essentially wired together at the busses, with extra instructions added with new logic in TTL silicon, I think it was for doing the maths for the vector graphics. It was amazing the amount of hardware hackery that was necessary to build these experimental systems.