A digital library is a collection of information that is stored and accessed electronically. The information stored in the library should have a topic common to all the data. For example, a digital library can be designed for computer graphics, operating systems, or networks. These separate libraries can be combined under one common interface that deals with computers, but it is essential that the information contained within each library remain separate. The purpose of a digital library is to provide a central location for accessing information on a particular topic. The last thing a user wants to happen when he searches for information about computer graphics is to get information on operating systems. A digital library must keep topics separate, otherwise it would be totally useless. A digital library should also have a user interface that is easy to use.

A digital library is a library in which collections are stored in digital formats (as opposed to print, microform, or other media) and accessible by computers.[1] The digital content may be stored locally, or accessed remotely via computer networks. A digital library is a type of information retrieval system.

As there are many definitions of a “digital library,” terms such as “electronic library” and “virtual library” are often used synonymously. A digital library is nothing but a large database for the people who are working on hypertext environment.

However an Electronic Library (E-library) is a library consisting of electronic materials and services. Thus the term “Electronic Library” encompasses all the material that can be held by a “digital library” and therefore more inclusive.

A Digital Library is a library consisting digital materials and services. Digital materials are items that are stored, processed and transform via digital devices and networks. Digital services are services (such as reference assistances) that are delivered digitally over computer networks. A good example is US Library of Congress American Memory Collection.

Virtual Library is the library that only exists virtually- that is the library does not exist “in a real life”. A virtual library can consist of material from a variety of separate libraries that are organized in a virtual space using computers and computer networks. A virtual library is a library for all practical purposes, but a library without walls-or books. A typical example is Nigerian Virtual Library by NUC. Both digital and electronic libraries can be virtual libraries.

Hybrid library is the library, which are working both in electronic or digital and print environment. However, the term hybrid library is sometimes used for libraries that have both physical collections and digital collections. It is estimated that in near future libraries will be of hybrid nature.

Digital libraries are full-text databases that replicate, in digital media, many of the functions of traditional libraries. They tend to contain a purposefully selected collection of texts plus various means of access to these texts. However, the limited buying power of libraries, complex nature of recent document, storage problems etc are some of the common factors which are influencing to change to digital mode, some other factors are-

1. Information explosion: The sudden increase in the number of people that request for the same information at the same time.

2. Searching problem in traditional libraries: The problem of looking for a text book on shelve or a “phrase” in a particular text book.

3. Low cost of technology: When we consider the storage capacity of digital document and its maintained then it can be easily realize that the cost of technologies is much more less than that of traditional libraries.

4. Environmental factor: The use of digital libraries is the cleanest technologies in today’s computing.

5. Technology Advancement: The need to follow the trend in Information Technology (IT)

The Internet and World Wide Web provide the impetus and technological environment for the development and operation of a digital library. The Internet provides the TCP/IP and or its associated protocol for accessing the information and web provide tools and technique for publishing the information over Internet using HTTP. Some of the other requirements for digital libraries are:

1. Audio and Visual: VGA monitor, DVD, Sound box, Telephone line etc.

2. Computer: Server, P.C. with multimedia, UPS, etc

3. Network: LAN, MAN, WAN or the Internet etc.

4. Printer: Laser printer or any other printer.

5. Scanner: H.P. Scan jet or other, Digital camera, etc.

6. Storage Devices: Optical storage device, CD-ROM, Flash Drive, etc.

7. Software: Any suitable software, which is interconnected and suitable for LAN and WAN connection.

The benefits of digital libraries as a means of easily and rapidly accessing books, archives and images of various types are now widely recognized by commercial interests and public bodies alike. The following are some of the benefits of digital library;

i. Reachable Library: With the presence of the Internet, people can have access to previously unreachable local, regional and international libraries. The user of a digital library need not to go to the library physically, but can access the library any where there is Internet connectivity.

ii. Availability: A major advantage of digital libraries is that people can gain access to the information round the clock. Users can have access to digital library any time of the day once they are connected to the Internet.

iii. Multiple Accesses: Different users at different locations can have access to the same resources simultaneously at the same time without disturbing one another.

iv. Easy Information Retrieval: Users are able to use any search term (word, phrase, title, name, or subject) to search the entire collection of the library easily. Digital libraries can provide very user-friendly interfaces, giving clickable access to its resources.

v. Long time Preservation. Digitization is a long-term preservation solution for physical collections, and also provides access to copies of materials without degradation from repeated use.

vi. Requires no Space: Digital libraries have the potential to store much more information, simply because digital information requires very little physical space to contain them and media storage technologies are more affordable than ever before.

vii. Low Cost of Maintenance: The cost of maintaining a digital library is much lower than that of a traditional library. A traditional library must spend large sums of money paying for staff, book maintains, rent, and additional books. Digital libraries do away with these fees.

viii. Value Added Services. Certain characteristics of objects, primarily the quality of images, may be improved. Digitization can enhance legibility and remove visible flaws such as stains and discoloration.

ix. Downloading: Text books can be downloaded from the library website by the users, either freely or to be purchased depending on their policy. In addition, anti-virus will scan through the materials before downloading so that users will not download virus to their computers.