On my first computer operation job, I met Mainframe. When I entered the computer room, there were tape drives and disk drives. A few 9-track magnetic tapes were placed on top of a trolley; each had a label on it. I looked up some photos from “9-track tape - Wikipedia", and here are what the tape drives and tapes look like.
The disk drive was bigger than nowadays washing machines, but its capacity was only 350MB, even smaller than our flash drive nowadays. A photo of a disk drive is available from “Photos of Computer Hard Drives Show How Much They've Shrunk (businessinsider.com)”.
The mainframe looked like a huge metal container, with several power cables and connection cables connected to it. I recalled that the air-conditioner broke down one time when we were running batch jobs, in which we could not shut down the mainframe. The computer room became as hot as a sauna. Eventually, the mainframe shut down by itself, then it took us nearly a day to restart and rerun all the batch jobs. A photo of a Mainframe is available from "IBM 4300 - Wikipedia".
~ Maniel, The Clallery