The Spagthorpe System/37 was …
Who am I kidding? There wasn’t any such thing. There wasn’t a mainframe that ran on 440 volt five cycle power, it didn’t make double use of its mercury delay lines for cooling, it didn’t use four-state logic in the ALU, the disk drives didn’t also work as washing machines for the system operators. There wasn’t a cot that pulled out from below blinkenlights on the front panel, there were no thudding relays that tripped whenever a program indirected through NULL by accident, divide-by-zero did not telephone the manufacturer and call a customer engineer in to replace the DIV0 fuse, and the main memory cabinet did not have a little seat and a small refrigerator inside so that salesmen could lurk for days on end, observing customers and their computing habits. There was no confettii option for the line printer, no way to make the tape drives spray multi-colored tape over the room or have the vacuum motors play tuba sounds, and you couldn’t re-route the B-supply line through the operator’s chair if you needed a new stack of cards put in the hopper. There was no spindle operation on the card reader, you couldn’t make the PC go backwards with a bit in the PSW, there wasn’t a way to power down the system and then bring it back up a few seconds later, and there was no secret instruction to make the disks spin backwards.
There should have been, but wasn’t.
Somehow, just sitting there and being a computer was sufficient.