I worked on an old IBM mainframe computer in 1987. It was powered up rarely, to test and maintain one program. Most of the time, it wasn't even turned on. The mainframe was just old, some of the peripherals were truly ancient. In particular, there was this one huge metal box. This box was from the era, when IBM made all of their cabinets so they just barely fit into the smallest common freight elevator.
This box was a disk controller. It was connected to the mainframe via the "channel interface". The disk drives it controlled were the washing machine sized thingies with the cake platter disks. They were newer than the controller, so they were on the order of 80Mbytes.
The controller had a stupid little processor of its own, so it could manage the conversations between the disk drives and the mainframe channel interface. This stupid little processor needed to load its software from somewhere.
The hard disk controller booted from the read only floppy disk drive, hidden in the cabinet. Once the controller finished booting, it turned off the floppy disk drive. It wouldn't access it again until the next boot. It had no need to write stuff to the floppy, because once it was up and running, it could save data to the big disk drives.
We had some spare parts. The data cables were about an inch in diameter. We had some that were the maximum safe length for one person to install. That is to say, the cables were 60 pounds each. If it was any longer, and therefore any heavier, OSHA rules required two people to lift it. The computer was in a machine room with raised floors. The huge cables ran under the floor between the cabinets.
The controller cabinet was mostly empty, but it looked impressive from the outside. When you bought hardware from IBM in the early 1970s, you got your money's worth (edit: or at least it looked that way. The thing cost more than a nice car).
It looked like cardboard to me. This wasn't one of those modern floppies like we had in 1975, that was used for saving and transporting data, this was just used for booting the peripherals. Something that happened once every few months, or less.
[Edit: Since this is now a quality post, I thought I should fix up the low quality grammar.]