BackgroundDuring the past thirty years digital libraries have gone from a curiosity to mainstream. The 1990s were a particularly formative decade. Before 1990 computing in libraries had concentrated on metadata. MARC cataloguing had reached its zenith, indexing services such as Medline had developed sophisticated search languages, and Science Citation Index was the state-of-art in linked data, but with very few exceptions the actual collections were physical items such as printed documents. About 1990, computing reached a level where it became economically possible to mount large collections online and to access them over networks. The result was a flurry of experiments and prototypes. Many are almost forgotten, yet the libraries of today were formed by the energy and creativity of these efforts. This article describes some of these projects and the impact that they have had on modern libraries.There was nothing inevitable about which prototypes succeeded in the long term. The Internet uses the TCP/IP family of protocols, but for many years the Open Systems Interconnection (OSI) framework was the choice of every major company. The early web was one of several competing ways to mount information online and had many weaknesses. Web searching did not have to be a free service paid for by advertising. Engineers might argue that the successful technology was technically superior, but cultural, economic, and social forces were at least as important in its adoption.The article is not a full history of the period that is covered. Many important projects have been skipped. A more complete article would have additional examples from the commercial sector and would do more to place the American experience in a worldwide context.
Before 1990Before there were computers, libraries were pioneers in using technology such as typewriters and microfilm. Beginning in the 1960s computing was widely used in libraries, but general-purpose computers such as the IBM 360 series were a long way from serving the needs of libraries. As a result, libraries developed specialized software that diverged from the mainstream of software development. Two early examples were the MARC format and Z39.50.