In its traditional sense, a 'library\' is a collection of books.
However, with the collection or invention of media other than books for storing information, many libraries are now repositories and/or access points for maps, printss or other artwork, microfilm, microfiche, audio tapes, CDss, LPss, video tapes and DVDs, and have facilities to use CD-ROM databases and the Internet.
Thus, modern libraries have been redefined as places to get access to information in any format, whether it is stored inside the building or not.
The modern library arose very directly from the historical fact that books were valuable, were therefore likely to be stolen, and were far too expensive to be owned by most people, and its architecture derived from the need to chain these books, first to lecterns and later to armaria and shelves, in areas that were illuminated by sunlight. Early libraries were based in cloisters associated with scriptoria and were collections of lecterns with books chained to them. Shelves built above and between back-to-back lecterns were the beginning of bookpresses. The chains were attached at the fore-edges of the books rather than their spines. Book presses came to be arranged in carrels (perpendicular to the walls and therefore to the windows) in order to maximize lighting, with low bookcases in front of the windows. This stall system (fixed bookcases perpendicular to exterior walls pierced by closely spaced windows) was characteristic of English institutional libraries. In Continental libraries, bookcases were arranged parallel to and against the walls. This wall system was first introduced on a large scale in Spain's El Escorial.
As books became cheaper, the need for chaining them lessened, but as the numbers of books in libraries increased, so did the need for compact storage and access with adequate lighting, giving birth to the stack system, which involved keeping a library's collection of books in a space separate from the reading room, an arrangement which arose in the 19th century. Bookstacks quickly evolved into a fairly standard form in which cast-iron and steel frameworks which supported the bookshelves also supported the floors, which were translucent to permit the passage of light (but not transparent, for purposes of modesty). With the introduction of electrical lighting, this use of glass floors was largely discontinued.
Ultimately even more space was needed, and the principles of moving shelves were devised to cut down on otherwise wasted aisle space.
Librarians need to let the public know what materials are present in their library, and the public needs to know how to access that information. Traditionally, this was accomplished by card catalogs, but the emergence of the Internet has led to the adoption of digital catalogs, which allow users to search the library's holdings from any location with Internet access. This style of catalog maintenance is compatible with new types of libraries, such as digital libraries and distributed libraries.
Though books are nowadays produced using a digital version of the content, for most books such a version is not available to the public (i.e. neither in the library nor on internet).
Basic tasks in library management include the planning of acquisition (which materials should be acquired), library classification, preservation of materials (especially rare and fragile materials such as manuscripts), borrowing, and developing and administering library computer systems. More long-term issues include the planning of the construction of new libraries or extensions to existing ones.