Hunter's Cub Scout group toured our movie theater. We were shown how they thread the film.
It is threaded through the brain and then over to the projector. The light bulb they use is a 2000 watt bulb. After turning the projector off you can't open it up for 15-20 minutes or it will bust and sound like a shot gun.
The film plays from one of the platter and reloads on another.