Operation
In its basic form, a tabulating machine would read one card at a time, print portions (fields) of the card on fan-fold paper, possibly rearranged, and add one or more numbers punched on the card to one or more counters, called accumulators. On early models, the accumulator register dials would be read manually after a card run to get totals. Later models could print totals directly. Cards with a particular punch could be treated as master cards causing different behavior. For example, customer master cards could be merged with sorted cards recording individual items purchased. When read by the tabulating machine to create invoices, the billing address and customer number would be printed from the master card, then individual items purchased and their price would be printed. When the next master card was detected, the total price would be printed from the accumulator and the page ejected to the top of the next page, typically using a carriage control tape.
With successive stages or cycles of punched-card processing, fairly complex calculations could be made if one had a sufficient set of equipment. (In modern data processing terms, one can think of each stage as an SQL clause: SELECT (filter columns), then WHERE (filter cards, or "rows"), then maybe a GROUP BY for totals and counts, then a SORT BY; and then perhaps feed those back to another set of SELECT and WHERE cycles again if needed.) A human operator had to retrieve, load, and store the various card decks at each stage.
Read more about this topic: Tabulating Machine
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