Unit record equipment

Starting at the end of the nineteenth century, well before the advent of electronic computers, data processing was performed using electromechanical machines called unit record equipment, electric accounting machines (EAM) or tabulating machines. Unit record machines came to be as ubiquitous in industry and government in the first two-thirds of the twentieth century as computers became in the last third. They allowed large volume, sophisticated data-processing tasks to be accomplished before electronic computers were invented and while they were still in their infancy. This data processing was accomplished by processing punched cards through various unit record machines in a carefully choreographed progression. This progression, or flow, from machine to machine was often planned and documented with detailed flowcharts that used standardized symbols for documents and the various machine functions. All but the earliest machines had high-speed mechanical feeders to process cards at rates from around 100 to 2,000 per minute, sensing punched holes with mechanical, electrical, or, later, optical sensors. The operation of many machines was directed by the use of a removable plugboard or control panel. Initially all machines were manual or electromechanical. The first use of an electronic component was in 1940 when a gas triode vacuum tube replaced a relay in an IBM card sorter. Electronic components were used on other machines beginning in the late 1940s.

IBM was the largest supplier of unit record equipment and this article largely reflects IBM practice and terminology.

In the 1880s Herman Hollerith invented the recording of data on a medium that could then be read by a machine. Prior uses of machine readable media had been for lists of instructions (not data) to drive programmed machines such as Jacquard looms and mechanized musical instruments. "After some initial trials with paper tape, he settled on punched cards [...]". To process these punched cards, sometimes referred to as "Hollerith cards", he invented the keypunch, sorter, and tabulator unit record machines. These inventions were the foundation of the data processing industry. The tabulator used electromechanical relays to increment mechanical counters. Hollerith's method was used in the 1890 census. The company he founded in 1896, the Tabulating Machine Company (TMC), was one of four companies that were consolidated to form the Computing-Tabulating-Recording Company (CTR), later renamed "International Business Machines" (IBM).

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