well i dont really know but the school i went to had a server and all i can say about its case was it was big and heavy lol. It had a lock on it (guess so that that no one can get in and steel things like RAM?) and it was really heavy to lift- wich was werid. other than that, i dont know- never seen inside one.
They fit ATX boards. The major difference is size so that its easier for the it guys to access and fix. Having said that, they do make very nice gaming machines and are great for the builder that likes to frequently get into the nitty gritty of their machine. Check out this link to see a really great server case that is near perfect. http://www.virtual-hideout.net/reviews/yeong_yang_cube_server_case/index.shtml