Punched tape

Punched tape or perforated paper tape is a form of data storage, consisting of a long strip of paper in which holes are punched to store data. Now effectively obsolete, it was widely used during much of the twentieth century for teleprinter communication, for input to computers of the 1950s and 1960s, and later as a storage medium for minicomputers and CNC machine tools.

Paper tapes constructed from punched cards were widely used throughout the 19th century for controlling looms. Perforated paper tapes were first used by Basile Bouchon in 1725 to control looms. However, the paper tapes were expensive to create, fragile, and difficult to repair. By 1801 Joseph Marie Jacquard had developed machines to create paper tapes by tying punched cards in a sequence. The resulting paper tape, also called a "chain of cards", was stronger and simpler both to create and to repair. (See Jacquard loom).

This led to the concept of communicating data not as a stream of individual cards, but one "continuous card", or a tape. Many professional embroidery operations still refer to those individuals who create the designs and machine patterns as "punchers", even though punched cards and paper tape were eventually phased out, after many years of use, in the 1990s.

In 1846, Alexander Bain used punched tape to send telegrams.

In 1880s, Tolbert Lanston invented a Monotype System, which consisted of a keyboard (typesetting machine) and a composition caster. The tape, punched with the keyboard, was later read by the caster, which produced lead type according to the combinations of holes in 0, one or more of 31 positions. The tape reader used compressed air, which passed through the holes and was directed into certain mechanisms of the caster. The system went into commercial use in 1897 and was in production well into 1970s, undergoing several changes along the way.

Data were represented by the presence or absence of a hole at a particular location. Tapes originally had five rows of holes for data. Later tapes had 6, 7 and 8 rows. An early electro-mechanical calculating machine, the Automatic Sequence Controlled Calculator or Harvard Mark I, used paper tape with 24 rows. A row of smaller sprocket holes that were always punched served to feed the tape, originally using a wheel with radial teeth called a sprocket wheel. Later optical readers used the sprocket holes to generate timing pulses. The sprocket holes are a bit to one side, making it clear which way to orient the tape in the reader. If you think of the sprocket holes as dividing the tape into unequal sides, the bits on the narrower side of the tape are generally the least significant bits, when the code is represented as numbers in a digital system.

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