The plugboard is more complex than earlier tabulators, where you would connect a wire from, say column 5 of the card input to column 12 of the print line. Or co

The plugboard is more complex than earlier tabulators, where you would connect a wire from, say column 5 of the card input to column 12 of the print line. Or connect a card column to a counter input. Most of the wiring for the older tabulators was pretty straightforward for customers, specifying how the characters moved when a card was read. The Univac 1004 made things more complicated in two ways. First, you had multiple steps; tabulators did one step per card (more or less). Second, the Univac 1004 had core memory, so characters were moving in and out of user-controlled storage locations, instead of directly from the card to the printer. There's a diagram on page 96 of the manual. Take a look and I'll see if I can explain: http://bitsavers.org/pdf/univac/1004/UT2543_1004_Card_Processor_80_Column_Reference.pdf http://bitsavers.org/pdf/univac/1004/UT2543_1004_Card_Proces... There are 31 holes for the "step output" (rows L through P on the panel). These get energized on steps 1 through 31 of the program. The basic idea is that you wire from a step output to everything that should happen during that step. You connect a wire from a step to the action you want to perform on that step. You also connect wires to select the two operands for the operation during this step. The core memory is arranged as a 31 by 31 matrix. (I think it's a coincidence that 31 matches the number of steps.) To write a value to the core memory, you give the memory the two coordinates by connecting two wires (rows j through m on the panel). For a branch, you wire to a Step Sequence Change input (row W), specifying which step should be executed next. There are a bunch of "selectors" which are like relays that select one of two inputs. These let you implement conditional actions based on a signal (without doing a branch). There are a bunch of "address combine" connections, which I think operate like AND gates, producing an output if there are multiple inputs. Because everything is wired electrically, you can't simply wire two outputs to the same input or they will get shorted together. So you have "distributors", which essentially produce multiple copies of the same signal. (Internally, it's just a diode.) The plugboard also has a lot of features that are useful for card-processing applications but may seem random, like suppressing leading zeros on a number. It's really a different model of programming from what you're used to. I haven't looked thoroughly at how the Univac 1004 gets wired up, so my explanation is a bit hand-waving. You can look at the manual if you want to learn more.