Plugboard
The program as a physical object: a board full of holes where the wires were the code.
The punch-card machines that grew out of Hollerith's technology were controlled by a removable panel — a board on which the operator ran wires from inputs to outputs to decide which columns got summed, compared and printed. Changing the job meant changing the board. Companies stored them on shelves like binders, labelled along the spine, and a fluent panel wirer was a valuable hire.
ENIAC inherited the idea at scale. Until 1948 the machine was set up with switches and cables strung between its twenty accumulators, which could take days for each new problem. When it was rebuilt that year to fetch instructions from its function tables it became roughly six times slower — and considerably more useful, because setup shrank from days to hours. Enigma's Steckerbrett was the same idea in miniature: a patch of cables that changed what the machine did.