A research library is a library which contains an in-depth collection of material on one or several subjects (Young, 1983; p.188). A research library will generally include primary sources as well as secondary sources. Large university libraries are considered research libraries, and often contain many specialized branch research libraries.
Research libraries can be either reference libraries, which do not lend their holdings, or lending libraries, which do lend all or some of their holdings. Some extremely large or traditional research libraries are entirely reference in this sense, lending none of their material; most academic research libraries, at least in the U.S., now lend books, but not periodicals or other material.
Digital libraries are libraries that house digital resources. They are defined as an organization and not a service that provide access to digital works, have a preservation responsibility to provide future access to materials, and provides these items easily and affordably. The definition of a digital library implies that "a digital library uses a variety of software, networking technologies and standards to facilitate access to digital content and data to a designated user community." Access to digital libraries can be influenced by several factors, either individually or together. The most common factors that influence access are: The library's content, the characteristics and information needs of the target users, the library's digital interface, the goals and objectives of the library's organizational structure, and the standards and regulations that govern library use. Access will depend on the users ability to discover and retrieve documents that interest them and that they require, which in turn is a preservation question. Digital objects cannot be preserved passively, they must be curated by digital librarians to ensure the trust and integrity of the digital objects.
One of the biggest considerations for digital librarians is the need to provide long-term access to their resources; to do this, there are two issues requiring watchfulness: Media failure and format obsolescence. With media failure, a particular digital item is unusable because of some sort of error or problem. A scratched CD-Rom, for example, will not display its contents correctly, but another, unscratched disk will not have that problem. Format obsolescence is when a digital format has been superseded by newer technology, and so items in the old format are unreadable and unusable. Dealing with media failure is a reactive process, because something is done only when a problem presents itself. In contrast, format obsolescence is preparatory, because changes are anticipated and solutions are sought before there is a problem.
Future trends in digital preservation include: Transparent enterprise models for digital preservation, launch of self-preserving objects, increased flexibility in digital preservation architectures, clearly-defined metrics for comparing preservation tools, and terminology and standards interoperability in real time.