Stanford and Northwestern are both in quarter system but at Stanford, classes typically worth between 3 and 5 units. Northwestern is weird in that virtually all classes count as 1 unit even some can be quite a bit more demanding than others. For STEM classes, each class in the intro year-long series is about 2/3 of the semester course but I think the first 2 quarters of organic chemistry cover more than 2/3 of the two semester course. The upper level science/engineering courses cover the same materials as those in semester system (so they are accelerated).