Initial Program Load (IPL) is a term from the mainframe world that describes the restart of an operating system ofmainframes.
The IPL process is similar to the booting of personal computers. Restarting operating systems was time-consuming in that program codes with a character count of many megabytes had to be loaded into main memory. Configuration changes required shutting down the system and changing the configuration files. With today's systems, reconfigurations take place dynamically during operation.