Microforms are analogue storage mediums for texts and images, often used for stable archiving. In air-conditioned environments, the type used has an estimated lifetime of 200 years; the type required for tropical climates has a shorter lifetime of 20 years. They require far smaller storage than paper documents. A microfilm version of a year of a periodical takes 10% of the space and 3% of the weight of the paper version. A microfiche version of the same version fits on one fiche and takes 0.05% of the space and weight of the paper version.
Each page or single sheet document is photographed as a single frame. The most standard form is black and white 35mm photographic film. Viewing is either by handheld magnifying glass or a magnification special reader.
Microfiche is more compact than microfilm. Each microfiche card holds about 100 - 130 pages depending on the size of the original. The most standard form is a clear plastic card, about 4ins by 6ins. The title of the work is usually in visible lettering along one edge. The most common reduction ratio is x24. As the image is too small to read, special readers are required to project full-size images on a ground-glass screen.
These are a specialised form of punch card for storing 'blueprints', such as engineering drawings. A drawing is photographed onto 35mm film and the image is mounted in a window on the right half of the punch card. Information about the drawing, e.g. the drawing number is punched on the left half.