NROTC pays fully for college but you'll be more involved outside of school-cruises, unit activities, etc. PLC pays a fair amount too. But you won't go on cruises, training, etc. Instead, you just have to stay in shape, maintain a certain GPA, then go to OCS. OCS pays nothing. You sign up to go to OCS sometime during college or after college, and you go.

thanks. is ocs very physically demanding, more so than NROTC

NROTC is a joke in comparison to OCS. However, ALL Marine officers go through OCS, including the NROTC ones. Btwn. jr. sr. year, you will attend OCS in the summer if you are in NROTC. PLC and OCSers get the same deal, just a few weeks longer to catch up on whatever the NROTC guys have that they haven't gotten yet. I think it's drill and basic military knowledge.