The 3B1 was one of the few uses of the 68010, which was basically a 68000 with a few bug fixes and, importantly, support for virtual memory. Combined with a separate MMU, this allowed you to run Unix.
The VM support was the killer feature. The 3B1 has a hardware (discrete logic!) MMU, a custom designed thing completely unlike the Motorola 68451. It's an odd beast and took a lot of work (by several people, not just myself; check the git commit logs and CREDITS) to get it right.
