Punched tape

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Five- and eight-hole punched paper tape PaperTapes-5and8Hole.jpg
Five- and eight-hole punched paper tape
Paper tape reader on an early computer with a small piece of five-hole tape connected in a circle - creating a physical program loop Harwell-dekatron-witch-10.jpg
Paper tape reader on an early 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 in which holes are punched. Now effectively obsolete, it was widely used during much of the 20th 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.



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. Jacquard.loom.cards.jpg
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.

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 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). 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.

In 1846, Alexander Bain used punched tape to send telegrams. This technology was adopted by Charles Wheatstone in 1857 for the preparation, storage and transmission of data in telegraphy. [1]

In 1880s, Tolbert Lanston invented the 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, 1, 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 the 1970s, undergoing several changes along the way.

Tape formats

A 24-channel program tape for the Harvard Mark I Harvard Mark I program tape.agr.jpg
A 24-channel program tape for the Harvard Mark I

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 six, seven and eight rows. An early electro-mechanical programmable calculating machine, the Automatic Sequence Controlled Calculator or Harvard Mark I, used paper tape with 24 rows. [2] 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 slightly to one side, making it clear which way to orient the tape in the reader and 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.[ citation needed ]

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 never used in teleprinters. Instead, modifications such as the Murray code (which added carriage return and line feed), Western Union code, International Telegraph Alphabet No. 2 (ITA 2), and American Teletypewriter code (USTTY), were used. [3] Other standards, such as Teletypesetter (TTS), FIELDATA and Flexowriter, had six holes. In the early 1960s, the American Standards Association led a project to develop a universal code for data processing, which became known as ASCII. This seven-level code was adopted by some teleprinter users, including AT&T (Teletype). Others, such as Telex, stayed with the earlier codes.


Tape for punching was 0.00394 inches (0.1 mm) thick. The two most common widths were 11/16 inch (17.46 mm) for five bit codes, and 1 inch (25.4 mm) for tapes with six or more bits. Hole spacing was 0.1 inch (2.54 mm) in both directions. Data holes were 0.072 inches (1.83 mm) in diameter; feed holes were 0.046 inches (1.17 mm).

Chadless tape

Most tape-punching equipment used solid 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 and interfere with the other electromechanical parts of the teleprinter equipment.

Chadless 5-level Baudot paper tape circa ~1975-1980 punched at Teletype Corp. 1980-Paper Tape fromTeletype (chadless, 5-level Baudot)-02.jpg
Chadless 5-level Baudot paper tape circa ~1975–1980 punched at Teletype Corp.

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

The word "Wikipedia", and a CR/LF as 7-bit ASCII, without a parity bit, least significant bit on the right - e.g. "W" is 1010111 Papertape-Wikipedia-example-dark1.svg
The word "Wikipedia", and a CR/LF as 7-bit ASCII, without a parity bit, least significant bit on the right - e.g. "W" is 1010111



Paper tape relay operation at US FAA's Honolulu flight service station in 1964 Honolulu IFSS Teletype1964.faa.jpg
Paper tape relay operation at US FAA's Honolulu flight service station in 1964

Punched tape was used as a way of storing messages for teletypewriters. Operators typed in the message to the paper tape, and then sent the message at the maximum line speed from the tape. This permitted the operator to prepare the message "off-line" at the operator's best typing speed, and permitted the operator to correct any error prior to transmission. An experienced operator could prepare a message at 135 words per minute (WPM) or more for short periods.

The line typically operated at 75WPM, but it operated continuously. By preparing the tape "off-line" and then sending the message with a tape reader, the line could operate continuously rather than depending on continuous "on-line" typing by a single operator. Typically, a single 75WPM line supported three or more teletype operators working offline. Tapes punched at the receiving end could be used to relay messages to another station. Large store and forward networks were developed using these techniques.

Paper tape could be read into computers at up to 1,000 characters per second. [4] In 1963, a Danish company called Regnecentralen introduced a paper tape reader called RC 2000 that could read 2,000 characters per second; later they increased the speed further, up to 2,500 cps. As early as World War II, the Heath Robinson tape reader, used by Allied codebreakers, was capable of 2,000 cps while Colossus could run at 5,000 cps using an optical tape reader designed by Arnold Lynch.


Software on fanfold paper tape for the Data General Nova minicomputer Dg-papertapes.jpg
Software on fanfold paper tape for the Data General Nova minicomputer

When the first minicomputers were being released, most manufacturers turned to the existing mass-produced ASCII teleprinters (primarily the Teletype Model 33, capable of ten ASCII characters per second throughput) as a low-cost solution for keyboard input and printer output. The commonly specified Model 33 ASR included a paper tape punch/reader, where ASR stands for "Automatic Send/Receive" as opposed to the punchless/readerless KSR – Keyboard Send/Receive and RO – Receive Only models. As a side effect, punched tape became a popular medium for low-cost minicomputer data and program storage, and it was common to find a selection of tapes containing useful programs in most minicomputer installations. Faster optical readers were also common.

Binary data transfer to or from these minicomputers was often accomplished using a doubly encoded technique to compensate for the relatively high error rate of punches and readers. The low-level encoding was typically ASCII, further encoded and framed in various schemes such as Intel Hex, in which a binary value of "01011010" would be represented by the ASCII characters "5A". Framing, addressing and checksum (primarily in ASCII hex characters) information helped with error detection. Efficiencies of such an encoding scheme are on the order of 35–40% (e.g., 36% from 44 8-bit ASCII characters being needed to represent sixteen bytes of binary data per frame).

Data transfer for ROM and EPROM programming

In the 1970s through the early 1980s, paper tape was commonly used to transfer binary data for incorporation in either mask-programmable read-only memory (ROM) chips or their erasable counterparts – EPROMs. A significant variety of encoding formats were developed for use in computer and ROM/EPROM data transfer. [5] Encoding formats commonly used were primarily driven by those formats that EPROM programming devices supported and included various ASCII hex variants as well as a number of proprietary formats.

A much more primitive as well as a much longer high-level encoding scheme was also used – BNPF (Begin-Negative-Positive-Finish). In BNPF encoding, a single byte (8 bits) would be represented by a highly redundant character framing sequence starting with a single ASCII "B", eight ASCII characters where a "0" would be represented by a "N" and a "1" would be represented by a "P", followed by an ending ASCII "F". These ten-character ASCII sequences were separated by one or more whitespace characters, therefore using at least eleven ASCII characters for each byte stored (9% efficiency). The ASCII "N" and "P" characters differ in four bit positions, providing excellent protection from single punch errors. Alternative schemes were also available where "L" and "H" or "0" and "1" were also available to represent data bits, but in both of these encoding schemes, the two data-bearing ASCII characters differ in only one bit position, providing very poor single punch error detection.

Cash registers

NCR of Dayton, Ohio, made cash registers around 1970 that would punch paper tape. Sweda made similar cash registers around the same time. The tape could then be read into a computer and not only could sales information be summarized, billings could be done on charge transactions. The tape was also used for inventory tracking, recording department and class numbers of items sold.

Newspaper industry

Punched paper tape was used by the newspaper industry until the mid-1970s or later. Newspapers were typically set in hot lead by devices like linotype machines. With the wire services coming into a device that would punch paper tape, rather than the linotype operator having to retype all the incoming stories, the paper tape could be put into a paper tape reader on the linotype and it would create the lead slugs without the operator re-typing the stories. This also allowed newspapers to use devices, such as the Friden Flexowriter, to convert typing to lead type via tape. Even after the demise of the Linotype/hot lead, many early "offset" devices had paper tape readers on them to produce the news-story copy.

If an error was found at one position on the six-level tape, that character could be turned into a null character to be skipped by punching out the remaining non-punched positions with what was known as a “chicken plucker". It looked like a strawberry stem remover that, pressed with thumb and forefinger, could punch out the remaining positions, one hole at a time.

Automated machinery

Paper tape reader on a computer numerical control (CNC) machine Paper tape reader on a CNC control 001.jpg
Paper tape reader on a computer numerical control (CNC) machine

In the 1970s, computer-aided manufacturing equipment often used paper tape. Paper tape was an important storage medium for computer-controlled wire-wrap machines, for example. A paper tape reader was smaller and less expensive than hollerith card or magnetic tape readers. Premium black waxed and lubricated long-fiber papers, and Mylar film tape were invented so that production tapes for these machines would last longer.


Vernam ciphers were invented in 1917 to encrypt teleprinter communications using a key stored on paper tape. During the last third of the 20th century, the National Security Agency (NSA) used punched paper tape to distribute cryptographic keys. The eight-level paper tapes were distributed under strict accounting controls and read by a fill device, such as the hand held KOI-18, that was temporarily connected to each security device that needed new keys. NSA has been trying to replace this method with a more secure electronic key management system (EKMS), but as of 2016, paper tape is apparently still being employed. [6] The paper tape canister is a tamper-resistant container that contains features to prevent undetected alteration of the contents.

Fanfold paper tape Papertape2.jpg
Fanfold paper tape


The three biggest problems with paper tape were:

  • Reliability. It was common practice to follow each mechanical copying of a tape with a manual hole-by-hole comparison.
  • Rewinding the tape was difficult and prone to problems. Great care was needed to avoid tearing the tape[ citation needed ]. Some systems used fanfold paper tape rather than rolled paper tape. In these systems, no rewinding was necessary nor were any fancy supply reel, takeup reel, or tension arm mechanisms required; the tape merely fed from the supply tank through the reader to the takeup tank, refolding itself back into exactly the same form as when it was fed into the reader.
  • Low information density. Datasets much larger than a few dozen kilobytes are impractical to handle in paper tape format.


Punched tape does have some useful properties:

Punched tape in art

A computing or telecommunications professional depicted in the Monument to the Conquerors of Space in Moscow (1964) holds what appears to be a punched tape with three rows of rectangular holes.

Current use

Nowadays punched tape use is very rare. It may still be used in older military systems[ citation needed ] and by some hobbyists. In computer numerical control (CNC) machining applications, very few people still use tape. However, some modern CNC systems still measure the size of stored CNC programs in feet or meters, corresponding to the equivalent length if punched on paper tape. [8]

See also

Related Research Articles

ASCII American computer character encoding

ASCII, abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Most modern character-encoding schemes are based on ASCII, although they support many additional characters.

Baudot code Pioneering five-bit character encodings

The Baudot code[bodo] is an early character encoding for telegraphy invented by Émile Baudot in the 1870s, It was the predecessor to the International Telegraph Alphabet No. 2 (ITA2), the most common teleprinter code in use until the advent of ASCII. Each character in the alphabet is represented by a series of five bits, sent over a communication channel such as a telegraph wire or a radio signal. The symbol rate measurement is known as baud, and is derived from the same name.

In computing and telecommunication, a control character or non-printing character (NPC) is a code point in a character set, that does not represent a written symbol. They are used as in-band signaling to cause effects other than the addition of a symbol to the text. All other characters are mainly printing, printable, or graphic characters, except perhaps for the "space" character.


The PDP-1 is the first computer in Digital Equipment Corporation's PDP series and was first produced in 1959. It is famous for being the computer most important in the creation of hacker culture at MIT, BBN and elsewhere. The PDP-1 is the original hardware for playing history's first game on a minicomputer, Steve Russell's Spacewar!

PDP-8 First commercially successful minicomputer

The PDP-8 is a 12-bit minicomputer that was produced by Digital Equipment Corporation (DEC). It was the first commercially successful minicomputer, with over 50,000 units being sold over the model's lifetime. Its basic design follows the pioneering LINC but has a smaller instruction set, which is an expanded version of the PDP-5 instruction set. Similar machines from DEC are the PDP-12 which is a modernized version of the PDP-8 and LINC concepts, and the PDP-14 industrial controller system.

Punched card paper-based recording medium

A punched card or punch card is a piece of stiff paper that can be used to contain digital data represented by the presence or absence of holes in predefined positions. Digital data can be used for data processing applications or, in earlier examples, used to directly control automated machinery.

Teleprinter device for transmitting messages in written form by electrical signals

A teleprinter is an electromechanical device that can be used to send and receive typed messages through various communications channels, in both point-to-point and point-to-multipoint configurations. Initially they were used in telegraphy, which developed in the late 1830s and 1840s as the first use of electrical engineering. The machines were adapted to provide a user interface to early mainframe computers and minicomputers, sending typed data to the computer and printing the response. Some models could also be used to create punched tape for data storage and to read back such tape for local printing or transmission.

The Cyclone, was a vacuum tube computer, built by Iowa State College at Ames, Iowa. The machine was placed into operation in July 1959. It was based on the IAS architecture developed by John von Neumann. The prototype of this machine is ILLIAC, the University of Illinois Digital Computer. The Cyclone used 40-bit words, used two 20-bit instructions per word, and each instruction had an eight-bit op-code and a 12-bit operand or address field. In general IAS-based computers were not code compatible with each other, although originally math routines which ran on the ILLIAC would also run on the Cyclone.

A telegraph code is one of the character encodings used to transmit information by telegraphy. Morse code is the most well known such code. Telegraphy usually refers to the electrical telegraph, but telegraph systems using the optical telegraph were in use before that. A code consists of a number of code points, each corresponding to a letter of the alphabet, a numeral, or some other character. In codes intended for machines rather than humans, code points for control characters, such as carriage return, are required to control the operation of the mechanism. Each code point is made up of a number of elements arranged in a unique way for that character. There are usually two types of element, but more element types were employed in some codes not intended for machines. For instance, American Morse code had about five elements, rather than the two of International Morse Code.

Friden Flexowriter

The Friden Flexowriter was a teleprinter, a heavy-duty electric typewriter capable of being driven not only by a human typing, but also automatically by several methods, including direct attachment to a computer and by use of paper tape.


A keypunch is a device for precisely punching holes into stiff paper cards at specific locations as determined by keys struck by a human operator. Other devices included here for that same function include the gang punch, the pantograph punch, and the stamp.

Teletype Model 33 1963—1981 ASCII communications / computer terminal device (keyboard printer paper tape)

The Teletype Model 33 is an electromechanical teleprinter designed for light-duty office use. It is less rugged and less expensive than earlier Teletype machines. The Teletype Corporation introduced the Model 33 as a commercial product in 1963 after being originally designed for the US Navy. There are three versions of the Model 33:

KDF8 was an early British computer built by English Electric as a version of the RCA 501. By producing a software-compatible system, the intention was to reduce time and cost to develop software. However, the lengthy process of developing manufacturing capability meant that the system was soon outpaced by systems from other vendors. Only a few systems were sold during its 5 years of production. Due to the consolidation of the British computer industry, English Electric's computer division became one of the components of what would become ICL.

Teletype Corporation

The Teletype Corporation, a part of American Telephone and Telegraph Company's Western Electric manufacturing arm since 1930, came into being in 1928 when the Morkrum-Kleinschmidt Company changed its name to the name of its trademark equipment. Teletype Corporation, of Skokie, Illinois, was responsible for the research, development and manufacture of data and record communications equipment, but it is primarily remembered for the manufacture of electromechanical teleprinters.

Computer programming in the punched card era

From the invention of computer programming languages up to the mid-1970s, most computer programmers created, edited and stored their programs line by line on punch cards.

Enquiry character transmission-control character that requests a response from the receiving station to see if it is still present; in ASCII, 0x05; in Unicode, U+0005

In computer communications, enquiry is a transmission-control character that requests a response from the receiving station with which a connection has been set up. It represents a signal intended to trigger a response at the receiving end, to see if it is still present. The response, an answer-back code to the terminal that transmitted the WRU signal, may include station identification, the type of equipment in service, and the status of the remote station.

The GEC 2050 was an 8-bit minicomputer produced during the 1970s, initially by Marconi Elliott Computer Systems of the UK, before the company renamed itself GEC Computers Limited. The first models were labeled MECS 2050, before being renamed GEC 2050.

Punched card input/output

A computer punched card reader or just computer card reader is a computer input device used to read computer programs in either source or executable form and data from punched cards. A computer card punch is a computer output device that punches holes in cards. Sometimes computer punch card readers were combined with computer card punches and, later, other devices to form multifunction machines. It is a input device and also an output device. Most early computers, such as the ENIAC, and the IBM NORC, provided for punched card input/output. Card readers and punches, either connected to computers or in off-line card to/from magnetic tape configurations, were ubiquitous through the mid-1970s.

Telex switched network of teleprinters

The telex network was a customer-to-customer switched network of teleprinters similar to a telephone network, using telegraph-grade connecting circuits for two-way text-based messages. Telex was a major method of sending written messages electronically between businesses in the post-World War II period. Its usage went into decline as the fax machine grew in popularity in the 1980s.

The Teletype Model 28 is a product line of page printers, typing and non-typing tape perforator and tape reperforators, fixed head single contact and pivoted head multi-contact transmitter-distributors, and receiving selector equipment. Regarded as the most rugged machines Teletype Corporation built, this line of teleprinters used an exchangeable type box for printing and sequential selector "Stunt Box" to mechanically initiate non-printing functions within the typing unit of the page printer, electrically control functions within the page printer and electrically control external equipment.


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  2. Dalakov, Georgi, History of computers: The MARK computers of Howard Aiken , retrieved 2011-01-12
  3. Proesch, Roland (2009). Technical Handbook for Radio Monitoring HF: Edition 2009. Books on Demand. ISBN   3837045730.
  4. Hult, Ture (1963), "Presentation of a new high speed paper tape reader", BIT Numerical Mathematics, 3 (2): 93–96, doi:10.1007/BF01935575
  5. "Translation File Formats" (PDF). Data I/O Corporation. Retrieved 2010-08-30.
  6. Tale of the Tape, NSA/CSS, May 3, 2016, Accessed June 16, 2014
  7. Sinha, N.K. (30 June 1986). Microprocessor-Based Control Systems. Springer. p. 264. ISBN   978-90-277-2287-4. Paper tape is well suited to a machine shop environment whereas magnetic tape may be accidentally erased or contaminated by foreign substances. ... Other disadvantages of paper tape are as follows ...
  8. Smid, Peter (2010). CNC Control Setup for Milling and Turning: Mastering CNC Control Systems. Industrial Press. p. 20. ISBN   978-0-8311-3350-4.