| Berkeley is on the semester system, UCLA is on the quarter. Signing up for classes can be a pain at Berkeley but UCLA can only be worse since
1) It's larger in size
2) It's on the quarter system (signing up for classes occurs more times in 1 yr)
Core academic classes (bio, chem, engineering, etc) can be hard to enroll in. So most usually sign up for those in Phase I. 4 hour long Chem labs can be a pain since they can fill up fast and ruin your planned schedule if you can't enroll in your preferred time. Classes with easier professors can fill up faster too.
Still, I have gotten into all my preferred courses at Berkeley, even with terrible Phase I times (b/c I'm a frosh). However, I did have to rearrange discussion sections and labs to other times. | 
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