Back in the day, there was only one movie showing, but you had the choice to see it at 7:00 or 9:00 (or during weekend matinees in the afternoon if you were so inclined). You could smoke in the balcony or the last 15 rows of the main auditorium floor and you usually got to see a cartoon or two before the main feature started.
There were two projectors in the booth and the movies were divided up on multiple reels. The projectionist would switch between the two projectors at a point in time that was noted by small marks that they made on the top right-hand corner of the film. When the first mark showed up on screen, the projectionist would start the second projector and let it run in tandem with the first one. The second mark would tell him when to switch over to the second projector and the new reel would be shown on the screen.
by ScurvyBagel