The most unusual feature of the Univac 1004 was that it was programmed by a plugboard (above) instead of a stored program.
The system was programmed by plugging patch cords into a plugboard to indicate the desired action for each of the 31 program steps.
While earlier electromechanical accounting machines used plugboards, that machine was obsolete by 1963.
The computer's "program" consisted of 31 steps.
The operations for each step were specified by plugging wires into the board.
For instance, a data field could be moved from a punch card to memory, a value could be added or subtracted, or a line of output could be configured for the printer.
The system even supported conditional branches.
The diagram below shows the structure of the plugboard. The highlighted wire shows a subtraction operation, activated by the wire in the "algebraic minus" position.