A microfiche is a single sheet of plastic that contains several images of pages of text, whereas microfilm is a long spool of plastic film that winds and rewinds to view images of text. In both instances, these microforms require a projection system whereby images of microfiche and microfilm appear on a backlit screen to be viewed.
Microfiche is usually 6 inches by 4 inches per sheet. Users place microfiche under a plate of glass. Once under the glass, light shines behind or beneath the plastic microfiche while a lens increases the image size. The image from the lens is then projected onto a small screen so individuals can read the text.
Microfilm is viewed in much the same way, only spools move microfilm back and forth under the plate of glass similar to a spool of movie celluloid. Microfilm holds many more document images than a single sheet of microfiche. Technology has improved to allow microfilm and microfiche images to be viewed on digital computer screens using special programs.
One of the largest microform collections in the world is housed at the Library of Congress. More than 7 million pieces can be viewed by researchers in the Microform Reading Room. The collection includes ancient manuscripts, posters, photographs, archives, rare publications and artifacts.