The most common type of microform is microfiche—flat strips of microfilm images stored in a clear Mylar sleeve or “jacket.” Jacket fiche comes primarily in two formats, 16mm and 35mm, and each sheet is about 4×6 inches.
COM fiche (Computer Output Microforms) are produced by printing computer-generated data directly onto film, creating the equivalent of hundreds of miniaturized documents arranged in a grid. COM fiche comes in two formats, 24x and 48x, referring to the reduction ratio (1/24th or 1/48th). Each COM fiche, about 105×148 mm, can hold up to 300 images due to its high reduction rate.
Microfilm or roll film is wound onto reels and can hold either 16mm or 35mm film, with 35mm more commonly used for large documents.