THE BIG HOUSE is, to my limited knowledge, the earliest prison film of the Sound Era and it's pretty damn good. It opens with a drunk driver getting booked into the prison on a manslaughter wrap. Right off the bat you can see this punk has a yellow streak a mile wide. Due to overcrowding he's thrown into a small cell with two hardened criminals. Time goes by and the new kid never toughens up. One of his cellmates escapes and goes to get his revenge on the kid (he hid a knife in his bunk and the screws found it) by killing(?) his sister, but instead he ends up falling in love with her and her with him. More stuff goes on, but you'll just have to see for yourself.
Modern audiences will probably find it way too dated, but if you give it a chance I think you'll enjoy it. Wallace Beery is tough as nails as a shit-talkin' murderer and was even nominated for an Oscar for his performance. He didn't win, but female screenwriter Frances Marion did win and ended up being the first female to win an Academy Award for writing.
Not the greatest prison film ever, but most definitely one of the most influential on the young genre. Check it out.