Yes, some prisons have some violence. We had a riot once where two people got shot. But it was very limited in scope and most of my time was very peaceful. Yes, there were occasions of one-on-one violence but, like I said, very rare.
In my (well over) 10 years, I had my walkman stolen (cellmate left our door open), had a tag-team knockdown and my pocket calculator stolen (and returned and a very convoluted retaliation followed), and had to throw a fellow inmate to the floor once. Not really that bad for the time I was there, eh?