IPL

IPL is Initial program load, used in operating system. In computing, booting is a bootstrapping method that starts operating systems when the user turns on a computer system. A boot series is the set of operations the computer performs when it is switched on that loads an operating system.

Most computer systems can only complete code found in the memory (ROM or RAM). Modern operating systems are stored on hard disks, or occasionally on Live CDs, USB flash drives, or other non-volatile storage devices. When a computer is first power-driven on, it doesn't have an operating system in memory. The computer's hardware alone cannot perform complex measures such as loading a program from disk, so an apparent paradox exists, to load the operating system into memory, one appears to need to have an operating system already loaded. The System/360 IPL function reads 24 bytes from an operator-specified or pre-configured machine into memory starting at location zero. The second and third groups of eight bytes are treated as Channel Command Words (CCWs) to maintain loading the startup program. When the I/O channel instructions are complete, the first group of eight bytes is then loaded into the Program Status Word (PSW) register and the startup program begins completing at the designated location.