I was in for 8 years, 1 month. I was never convicted. I was just in jail because I didn't have the money to bail out, otherwise I would not have spent a day inside.
It's not like the movies at all. All the races talked to each other and were pretty respectful. If there was a fight it was usually enforced to be only one-on-one. Every now and again someone from a person's gang would back him up in a fight, but it wasn't necessarily race-specific as the gangs have become very multicultural - you'll find Latino gangs with blacks and vice-versa. Often it's because people are so mixed now - is the guy black, mixed, Latino? Who knows?
I would change the prison system by practically abolishing the prison system. I don't think putting people in a box helps them. Almost every single person I met in jail was in there because of a raft of mental health issues that made it so their brain said committing a crime was OK and fuck the possible consequences. We need vastly more mental health support, especially for men who typically are not open about their weaknesses.