thumb|Five- and eight-hole wide punched paper tape

thumb|Creed model 6S/2 5-hole paper tape reader

thumb|Paper tape reader on the [[Harwell computer with a small piece of five-hole tape connected in a circle – creating a physical program loop]]

Punched tape or perforated paper tape is a form of data storage that consists of a long strip of paper through which small holes are punched. It was developed from and was subsequently used alongside punched cards, the difference being that the tape is continuous.

Punched cards, and chains of punched cards, were used for control of looms in the 18th century. Use for telegraphy systems started in 1842. Punched tapes were used throughout the 19th and for much of the 20th centuries for programmable looms, teleprinter communication, for input to computers of the 1950s and 1960s, and later as a storage medium for minicomputers and CNC machine tools. During the Second World War, high-speed punched tape systems using optical readout methods were used in code breaking systems. Punched tape was used to transmit data for manufacture of read-only memory chips.

History

thumb|upright|A paper tape, constructed from [[punched cards, in use in a Jacquard loom. The large holes on each edge are sprocket holes, used to pull the paper tape through the loom.]]

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 for Jacquard looms. The resulting paper tape, also called a "chain of cards", was stronger and simpler both to create and to repair. This led to the concept of communicating data not as a stream of individual cards, but as one "continuous card" (or tape). Paper tapes constructed from punched cards were widely used throughout the 19th century for controlling looms. 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 in the 1990s.

In 1842, a French patent by Claude Seytre described a piano playing device that read data from perforated paper rolls. By 1900, wide perforated music rolls for player pianos were used to distribute popular music to mass markets.

thumb|left|Wheatstone slip with a dot, space and a dash punched, and perforator punch plate

In 1846, Alexander Bain used punched tape to send telegrams. This technology was adopted by Charles Wheatstone in 1857 for the Wheatstone system used for the automated preparation, storage and transmission of data in telegraphy. Australia's 1951 electronic computer, CSIRAC, used wide paper tape with twelve rows.

Materials

Many early machines used oiled paper tape, which was pre-impregnated with a light machine oil, to lubricate the reader and punch mechanisms. The oil impregnation usually made the paper somewhat translucent and slippery, and excess oil could transfer to clothing or any surfaces it contacted. Later optical tape readers often specified non-oiled opaque paper tape, which was less prone to depositing oily debris on the optical sensors and causing read errors. Another innovation was fanfold paper tape, which was easier to store compactly and less prone to tangling, as compared to rolled paper tape.

For heavy-duty or repetitive use, polyester Mylar tape was often used. This tough, durable plastic film was usually thinner than paper tapes, but could still be used in many devices originally designed for paper media. The plastic tape was sometimes transparent, but usually was aluminized to make it opaque enough for use in high-speed optical readers.

Dimensions

Tape for punching was usually thick. The two most common widths were for five bit codes, and for tapes with six or more bits. Hole spacing was in both directions. Data holes were in diameter; sprocket feed holes were .

Chadless tape

thumb|left|Chadless 5-level Baudot paper tape punched at Teletype Corp

Most tape-punching equipment used solid circular punches to create holes in the tape. This process created "chad", or small circular pieces of paper. Managing the disposal of chad was an annoying and complex problem, as the tiny paper pieces had a tendency to escape containment and to interfere with the other electromechanical parts of the teleprinter equipment. Chad from oiled paper tape was particularly problematic, as it tended to clump and build up, rather than flowing freely into a collection container.

A variation on the tape punch was a device called a Chadless Printing Reperforator. This machine would punch a received teleprinter signal into tape and print the message on it at the same time, using a printing mechanism similar to that of an ordinary page printer. The tape punch, rather than punching out the usual round holes, would instead punch little U-shaped cuts in the paper, so that no chad would be produced; the "hole" was still filled with a little paper trap-door. By not fully punching out the hole, the printing on the paper remained intact and legible. This enabled operators to read the tape without having to decipher the holes, which would facilitate relaying the message on to another station in the network. Also, there was no "chad box" to empty from time to time.

A disadvantage to this technology was that, once punched, chadless tape did not roll up well for storage, because the protruding flaps of paper would catch on the next layer of tape so it could not be coiled up tightly. Another disadvantage that emerged in time was that there was no reliable way to read chadless tape in later high-speed readers which used optical sensing. However, the mechanical tape readers used in most standard-speed equipment had no problem with chadless tape, because they sensed the holes by means of blunt spring-loaded mechanical sensing pins, which easily pushed the paper flaps out of the way.

Encoding

thumb|upright|The word "Wikipedia", and a [[Newline|CR/LF as 7-bit ASCII, without a parity bit, least significant bit on the right—e.g. "W" is 1010111]]

Text was encoded in several ways. The earliest standard character encoding was Baudot, which dates back to the 19th century and had five holes. The Baudot code was superseded by modified five-hole codes such as the Murray code (which added carriage return and line feed) which was developed into the Western Union code which was further developed into the International Telegraph Alphabet No. 2 (ITA 2), and a variant called the American Teletypewriter code (USTTY).

  • A song mentioning paper tape
  • Various punched media
  • Olympia Flexowriter
  • Detailed description of two paper tape code systems, Baudot code and the system used by the ILLIAC computer
  • Working paper tape punch/reader GNT 3601, Musée Bolo, YouTube