As usual, a fascinating read! Maybe interesting in context, this page contains a description of how the DEC PDP-1 (announced the same year as the 1401) did it,

As usual, a fascinating read! Maybe interesting in context, this page contains a description of how the DEC PDP-1 (announced the same year as the 1401) did it, using bootstrap code and a loader format that can be traced back to the TX-0: https://www.masswerk.at/spacewar/inside/insidespacewar-spacewar2bsa5.html https://www.masswerk.at/spacewar/inside/insidespacewar-space...