Delete comment from: Ken Shirriff's blog
PJ, IPL stands for Initial Program Loader, and when the LOAD button was pressed the program it executed was called the "Bootstrap" program - A bootstrap was the little loop at the back of a boot to pull it on by, so a bootstrap program was a little program that got your program in and started.
Other manufacturers did not have an IPL button like IBM, and I've even had to do an IPL by actually keying the bootstrap program via front panel keys!
Usually the bootstrap program consisted of two instructions - Read 1 record from the boot device into a memory location then branch to that location. Therefore that record had to contain the "real" loader program, which would then load and execute your program.
Nov 9, 2019, 7:02:38 PM
Posted to Iconic consoles of the IBM System/360 mainframes, 55 years old