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Revision as of 10:41, 27 February 2007
Initial program load or IPL (sometimes pronounced as /ɪpl̩/) is a term for the start-up phase of a computer's operation. It is used mainly in connection with IBM and IBM mainframe and AS/400 computer systems. Bootstrapping, booting, and bootstrap loading are common synonyms for IPL.
IBM uses the term in preference to the more informal and less descriptive terms booting or bootstrapping. The term was invented by IBM for the design of the System/360, with the intent of replacing “bootstrapping,” and continues to be used in IBM technical documents today, such as the z/Architecture Principles of Operation (see Chapter 17).
In IBM mainframe systems that share the System/360 heritage—and in some other mainframes from other vendors that have been inspired by it—IPL is a hardware function in which a predefined I/O channel command is initiated to a selected device directly, causing a startup program to be loaded without the assistance of a “bootstrap routine.” The exact same procedure is used to boot from any device, including disk drives, tape drives, or even card readers, in a non-device-specific manner.