There are several formats for smaller format movie film. The first was 16mm, which is 16mm wide and has perforations on both sides of the film. It was made this width deliberately because they didn't want people slicing 35mm film in half. 16mm was made only on safety base film. Later they made regular old 8mm, now called double-8. This had twice as many perforations, and was run through the camera twice, forward and backwards. It was slit after processing and spliced in the middle. The reels are normally 25 ft long (to make 50 feet of slit film) but some cameras accepted 100 foot loads. Now someone (kodak) realized that the perforations were needlessly large. By shrinking the perforation dramatically they formed Super-8, with a much larger image and room for soundtrack. Fuji released a competing system called Single-8 which is the same size film but on a different base and a cartridge allowing full reverse movement of the film. A format called double super-8 was released as well which runs the same as double 8 but has smaller perforations.