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In the IBM System/360 and its successors, including the current z/Architecture machines, the boot process is known as Initial Program Load (IPL).

IBM coined this term for the 7030, revived it for the System/360, and continues to use it in those environments today.

The disk, tape or card deck must contain a special program to load the actual operating system or standalone utility into main storage, and for this specific purpose "IPL Text" is placed on the disk by the stand-alone DASDI (Direct Access Storage Device Initialization) program or an equivalent program running under an operating system, e.g., ICKDSF, but IPL-able tapes and card decks are usually distributed with this "IPL Text" already present.

IPL Command

IPL is both the name of the boot process and the actual command that is used to boot a virtual operating system running under VM (usually CMS, or Linux, but could also be z/TPF, z/VSE or z/OS).