Projectors are classified by the size of the film used, i.e. the film format.
Typical film sizes:

8 mm

Long used for home movies before the video camera, this uses double sprocketed 16 mm film, which is run through the camera twice. The 16 mm film is then split lengthwise into two 8 mm pieces that are sliced to make a single projectable film with sprockets on one side. See the 8 mm film article for more information.

Super 8

Developed by Kodak this film stock uses very small sprocket holes close to the edge that allow more of the film stock to be used for the images. This increases the quality of the image. The film is premade in the 8 mm width, not split during processing as is the earlier 8 mm. Magnetic stripes could be added to carry
encoded sound to be added after film development. See the Super 8 mm film article for more information.

16 mm

This was a popular format for audio-visual use in schools and as a high-end home entertainment system before the advent of broadcast television. It is also the smallest format that can carry an optically encoded sound track. See the 16 mm film article for more information.

35 mm

The most common film size for theatrical productions during the first half of the 20th century. In fact, the common 35 mm camera, developed by Leica was designed to use this film stock and was originally intended to be used for test shots by movie directors and cinematographers. See the 35 mm film article for more
information.

70 mm

High end movie productions are often shot using this size and some theaters are capable of projecting it. 70 mm film is also used in both the flat and domed IMAX projection system. In IMAX the film is oriented for even more effective image area than in other formats.

Some high quality productions intended for 35 mm anamorphic release are shot in and the master prints constructed using 70 mm film stock. A 35 mm print made from a 70 mm master print is significantly better in appearance than an all 35 mm process.

This article is licensed under the GNU
Free Documentation License. It uses material from the
Wikipedia article “Movie Projector”

History of 3M Overhead Projectors
(Dates Are Approximate)