I think it was basically since Saab was fairly early to the coil pack game, these "Direct Ignition Cassettes" was in production in 88...

Yeah... no standard knock sensor, which is the normal way to do things, but it's much improved because a regular knock sensor on a 900 can't really tell, what cylinder is knocking (and no cylinder behaves the same, regardless of what you do), so on a distributed 900 with the Bosch systems, it'll hold boost back or (with ezk) retard knocking for a few full cycles.

With ionization it can determine -which- cylinder is knocking and adjust timing and fuel on that one specifically

Here's a good article

https://eeuroparts.com/blog/tech-corner-saab-trionic-and-ion...