A definitive software library (DSL) is a secure location, consisting of physical media or a software repository located on a network file server, in which the definitive authorized versions of all software configuration items (CIs) are stored and protected. The DSL is separate from development, quality assurance or production software storage areas. It contains master copies of all controlled software and includes definitive copies of purchased software, as well as licensing information for software developed on-site or purchased from an external vendor. All related documentation, related to any software stored in the DSL, is also stored in the DSL.
Following the publication of ITIL version 3, the Definitive Software Library was renamed the Definitive Media Library.