When I first started working as a computer operator, in what was then called Data Processing, in the late 1970s the smaller IBM S/370 mainframes (the 115 and 125 models only, I think) had their IPL microcode on 12" floppy disks. You always needed to have a spare in case the one you usually IPLed from had a read error. There was a small cupboard thing under the CPU console printer where the floppy drive was located.
