Quoted from bobwiley:
Why were the rules different on SS vs. EM? What would be a minor difference and the most significant difference in the rules?
On EM multiplayers it wasn't impossible, in fact it had been done, but by the late 70s they chose to not have any carry over from ball to ball. What that means is the entire bonus would count down and the playful would completely reset after each ball and start over. So basically every ball played started out the same.
And on the EM Joker Poker for example, once the drop targets got knocked down, they stayed down until the ball was over so basically that was it. The solid state version would reset the targets once down so you could continue on.
What solid state really brought to the table, though I'm not sure how many of these utilized it yet, was memory. So as each player took a turn the playfield could be setup as he left it after his last turn, and not completely reset like all late model multiplayer EMs.
This is why in many cases single player EMs are more popular, because they don't reset after each ball and the game is allowed to progress, although there are a very few older multiplayers with some playfield memory. And why they all but disappeared once solid state took over.
The EM multiplayers I know of that had some sort of playfield or holdover memory prior to this were WMS Piccadilly from 1956, WMS Pit Stop, WMS 8-Ball, and GTB Scuba.