How does it work?

This is the machine which projects film onto the screen. Big, isn't it. It weighs 300kg.
Film has holes on each side and is drawn down into the machine by toothed sprockets driven by a powerful electric motor.
The sprockets pull the film into position and stop it. The shutter opens to shine light through the stationary film frame. The image is magnified about 300,000 times by the lens and projected onto the screen.
The stationary film frame is then pulled out of the way, and the next film frame held steady, to be projected on screen.
This process happens 24 times per second. This is fast enough for your brain to fill in the gaps and experience the film not as a series of still images, but a constantly flowing scene.
One second of on-screen action needs nearly half a metre of film! An entire feature film would stretch from here to the Astoria Cinema in Ayr, and a bit beyond.