I got really disappointed at the mainframe booting into PC-DOS with a CGA font on a 3278 terminal. The show made such an impeccable job at rebuilding the 3033 CPU and the 3278 terminal just to make such a horrible job depicting its boot process. A VM/SE banner or an MVS login screen would have been sufficient (if inaccurate, if we are looking at the operator console). Did the research point out mainframes don't run PC operating systems?