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The IBM 557 Alphabetic Interpreter allowed holes in punch cards to be interpreted and the Hollerith punch card characters printed on any row or column, programmed by the means of a wiring plug board. The machine was a synchronous system where brushes would glide over a hole in a punch card and contact a brass roller thereby setting up part of a character code.
The IBM 557 was an immensely complex electro-mechanical unit record machine. It contained large arrays of vacuum tubes (valves), wire-contact relays, cams, interlocks and gears. It hosted complex mechanisms called the rack and wheel unit, and the print unit. Engineers maintaining these machines were specially trained to repair them. In Australia, the last two engineers ever to be trained on these these were IBM engineers David Byrne and Winston Chin-Lenn in late 1979.
There are no 557's operating commercially in the world today.
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