The term digital library was first popularized by the NSF/DARPA/NASA Digital Libraries Initiative in 1994. With the availability of the computer networks, the information resources are expected to stay distributed and accessed as needed, whereas in Vannevar Bush’s essay As We May Think (1945) they were to be collected and kept within the researcher’s Memex.
The term virtual library was initially used interchangeably with digital library but is now primarily used for libraries that are virtual in other senses (such as libraries that aggregate distributed content). In the early days of digital libraries, there was a discussion of the similarities and differences between the terms digital, virtual, and electronic.
A distinction is often made between content that was created in a digital format, known as born-digital, and information that has been converted from a physical medium, e.g. paper, through digitization. Not all electronic content is in digital data format. The term hybrid library is sometimes used for libraries that have both physical collections and electronic collections. For example, American Memory is a digital library within the Library of Congress.
Some important digital libraries also serve as long term archives, such as arXiv and the Internet Archive. Others, such as the Digital Public Library of India, seek to make digital information from various institutions widely accessible online.
