Unit Record Equipment
Control panels were introduced in 1906 for a Hollerith tabulator. Earlier machines had been hard wired for specific applications. Removable control panels were introduced with the Hollerith (IBM) type 3-S tabulator in the 1920s. Applications then could be wired on separate control panels, and inserted into tabulators as needed. Tabulator functions were implemented with both mechanical and electrical components. Control panels simplified the changing of electrical connections for different applications, but changing most tabulator's use still required mechanical changes. The IBM 407 was the first IBM tabulator that did not require such mechanical changes; all the 407's functions were electrically controlled and were completely specified by the application's control panel and carriage tape. Removable control panels came to be used in all unit record machines where the machines use for different applications required rewiring. For most machines with control panels, from collators, interpreters, to the IBM 407, IBM manuals describe the control panel as "directing" or "automatic operation was obtained by...". The control panels of calculators, such as the IBM 602 and IBM 604, that specified a sequence of operations, were described as being a program.
IBM removable control panels ranged in size from 6 1/4" by 10 3/4" (for machines such as the IBM 077, IBM 550, IBM 514) to roughly one to two feet (300 to 600 mm) on a side and had a rectangular array of hubs. Plugs at each end of a patch cord were inserted into hubs, making a connection between two contacts on the machine when the control panel was placed in the machine, thereby connecting an emitting hub to an accepting or entry hub. For example, in a card duplicator application a card column reading (emitting) hub might be connected to a punch magnet entry hub. It was a relatively simple matter to copy some fields, perhaps to different columns, and ignore other columns by suitable wiring. Tabulator control panels could require dozens of patch cords for some applications.
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