Document Medium refers to the material upon which the original document was recorded.
Paper is a medium traditionally used for printed books and other documents that are the most frequent target of preservation efforts. Paper is defined to be sheets usually made of vegetable fibers laid down on a fine screen from a water suspension. Marks are imprinted on the paper using any of a number of techniques including handwriting or drawing using a variety of media such as pencil, pen and ink, or pastel; various forms of printing using inks (numerous technologies are used to accomplish this); photographic printing, where paper coated with light-sensitive emulsion is exposed to various intensities of light); xerographic printing, where an electrically charged photoconductive insulating surface is selectively exposed to light and the latent image is developed with a resinous powder; thermographic printing, where the paper is exposed to a directed heat source that selectively modifies parts of the surface that may have been pre-treated with a heat-sensitive powder; and chemical transfer printing, where the surface of the paper is chemically coated and selectively modified by pressure or other means.
Parchment and vellum are not paper since they are made from the skins of sheep, goats, or calfskin. [7] We note them here for completeness.
Hard Copy is a term often used to denote any document produced on paper.
Microform refers to a document medium for producing or reproducing printed matter. It records microimages, that is, images too small to be read without some form of magnification. In a general sense, microforms may be on film (1.1.4) or paper (1.1.1), but for purposes of this Glossary the definition is restricted to film. Reading a microform requires the assistance of a microform reader (3.6.2.2). Microform comes in different styles including microfilm (a film roll that contains microimages arranged sequentially) and microfiche (sheets of film in which many microimages are arranged in a grid pattern). Both usually contain a header that can be read without magnification).
Microforms are an economic and compact form of document representation for archival storage, but are inconvenient to read when compared with a printed book. Microform technology is used as a preservation medium (3.1.4), as a means of saving space (such as for the convenient storage of newspapers), or as a means of duplicating scarce or unique documents, that is, microreproductions of other original documents. However, microform is sometimes used for original documents, for example, those created on a computer and directly printed out onto a computer-output-on-microfiche (COM) device; and for microreproductions of material assembled for the purposes of releasing an original edition in microform.
Video is normally an analog (see definition under 1.1.6) electronic technology for recording still or moving images, usually combined with sound (cf. 1.1.5). Following standards (which vary across the world) defined for television playback and broadcasting, the images are normally recorded on magnetic tape (3.3.1.6.2), when it is known as videotape, but also on other physical media such as optical disk (3.3.1.6.3) (videodisk).
Playback is usually achieved through a television set or video projector (3.6.2.3), although it is now possible and becoming common to play video recordings back through a computer (3.6.2.6) or multimedia workstation (3.6.2.7).
Film is a recording medium consisting of thin sheets or strips of transparent or translucent material, such as polyester or acetate, coated with a light-sensitive emulsion. Recording occurs by exposing the film to the light emitted or reflected by the entity being recorded. Film is also the medium used for microfilm recording (1.1.2). A photograph (1.2.9.3) is produced using essentially the same technology, except that normally the light- sensitive emulsion is adhered to paper or some other opaque medium.
Audio documents are recordings made on a variety of (usually) magnetic media (see 3.3.1.6) of sounds only (as contrasted with video recordings (1.1.3) that also combine images). The evolution of such audio recordings has traversed a large number of different formats and physical media, including phonograph disks (records) of varying size (78 rpm's. 45 rpm's, 33 rpm's) and tape cassettes (of different formats), both of which are analog (see 1.1.6) recording technologies; and, more recently, compact disks and digital acoustic tapes (DATs), which are digitally (1.1.6) encoded.
Digital Electronic Technologies [8] are technologies used to capture (3.2.3), store (3.3.1.6), transform (3.3.2, 3.3.4, 3.3.2, 3.3.4), distribute (3.5.1.6) or present (3.6.1.6, 3.6.2.6, 3.6.2.7) information in quantized electronic form (normally as a sequence of O's and l's known as bits). Digital, in which information is quantized discretely, is to be contrasted with Analog, in which information is not quantized but maintained in a continuous format. [9] A video recording (1.1.3), is an example of an electronic technology that is analog [10].
For a variety of reasons, digital technologies are gradually replacing analog technologies. Reasons of importance to this Glossary are the convertibility of digital technologies among each other and into and from other technologies (such as paper and voice), so that digital technologies become a kind of lingua franca of communication and storage; and the ease of transmission of information by digital technologies across networks (3.5.5) to facilitate communication at a distance.
Original documents that are of concern for library preservation purposes are not normally encoded in a digital electronic medium. [11] Since this may become a subject of future concern, the category is included for completeness. Definitions, however, are more appropriately included under Storage Technology Medium (3.3.1.6).
Multi-Media is a term used to denote documents created using a number of different media simultaneously, usually those with an electronic technological basis: for example, a digital electronic recording (1.1.6) that also combines video (1.1.3) and audio (1.1.5), and that may, as part of the document, intrinsically produce paper (1.1.1) outputs.
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