I did 3 years in Federal Prison camp after Operation Raw Deal in 2007, then halfway house and 3 years of supervised release when I came home. Spent a few weeks in county jail after I was arrested, until I got a private lawyer (as opposed to a terrible public defender) who could get me out until my trial and sentencing.
In county jail everybody was all in gen pop together, no matter what their crime was. I was there for steroid distribution, but I had friends who were there for capital murder, for being coke kingpins, and then the losers who were just there because they beat up their girlfriend or got caught driving drunk. No weights, but we could do pushups, pullups, bodyweight squats and other exercises. The food was absolute crap but guys would give me extra cartons of milk and meat because they could see I was a big bodybuilder and they wanted to stay on my good side LOL. Guys in jail had nothing to do all day, so they would get into fights just out of sheer boredom, for nothing at all other than feeling disrespected by another guy. And everything in jail was very racially segregated: you had the white guy's TV (tuned to CNN or MTV), the black guy's TV (tuned to BET), and the Hispanic guy's TV (tuned to Telemundo), and guys generally socialized within their own racial groups. Jail sucked.
Federal prison camp was mostly just boring. I was lucky to be in a place where they had a great weight pile, and could lift as much as I wanted. The food still sucked, but you could pay other inmates to smuggle chicken or eggs or milk cartons out of the kitchen for extra protein. There were still fights, but most guys who were smart didn't want to fight because they didn't want to get sent to another prison with higher security (a low or medium or max, as opposed to a minimum security camp.) Things were still racially segregated to a certain extent, but not nearly as much as county jail. I was there doing a short bit (3 years), but I had plenty of friends who were finishing up long sentences...17 years, 23 years, 28 years...and that helped keep everything in perspective.
In a way, being in prison reminded me of my time in the military. It helped teach me a lot about myself, how I could get along with others who were different from me, and how to make do with very little. There were positive things that I learned there, although I never want to go back there again. But I could go back if I had to; it's nothing to be afraid of. I made friends there that I still keep in contact with today, there are good people in prison just like anywhere else in life.