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A teleprinter (teletypewriter, teletype or TTY) 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 In telecommunications, point-to-multipoint communication (P2MP, PTMP or PMP) is communication which is accomplished via a distinct type of one-to-many connection, providing multiple paths from a single location to multiple locations. Point-to ...
configurations. Initially they were used in telegraphy, which developed in the late 1830s and 1840s as the first use of electrical engineering, though teleprinters were not used for telegraphy until 1887 at the earliest. The machines were adapted to provide a
user interface In the industrial design field of human–computer interaction, a user interface (UI) is the space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine fr ...
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 (either from typed input or from data received from a remote source) and to read back such tape for local printing or transmission. Teleprinters could use a variety of different communication media. These included a simple pair of wires; dedicated non-switched telephone circuits (leased lines); switched networks that operated similarly to the
public telephone network The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local teleph ...
( telex); and radio and
microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency rang ...
links (telex-on-radio, or TOR). A teleprinter attached to a modem could also communicate through standard switched public telephone lines. This latter configuration was often used to connect teleprinters to remote computers, particularly in time-sharing environments. Teleprinters have largely been replaced by fully electronic computer terminals which typically have a
computer monitor A computer monitor is an output device that displays information in pictorial or textual form. A discrete monitor comprises a visual display, support electronics, power supply, housing, electrical connectors, and external user controls. The d ...
instead of a printer (though the term "TTY" is still occasionally used to refer to them, such as in Unix systems). Teleprinters are still widely used in the aviation industry (see
AFTN The Aeronautical Fixed Telecommunications Network (AFTN) is a worldwide system of aeronautical fixed circuits provided, as part of the Aeronautical Fixed Service, for the exchange of messages and/or digital data between aeronautical fixed stations ...
and
airline teletype system The airline teletype system uses teleprinters, which are electro-mechanical typewriters that can communicate typed messages from point to point through simple electric communications channels, often just pairs of wires. The most modern form of the ...
), and variations called
Telecommunications Devices for the Deaf A telecommunications device for the deaf (TDD) is a teleprinter, an electronic device for text communication over a telephone line, that is designed for use by persons with hearing or speech difficulties. Other names for the device include tel ...
(TDDs) are used by the
hearing impaired Hearing loss is a partial or total inability to hear. Hearing loss may be present at birth or acquired at any time afterwards. Hearing loss may occur in one or both ears. In children, hearing problems can affect the ability to acquire spoken ...
for typed communications over ordinary telephone lines.


History

The teleprinter evolved through a series of inventions by a number of engineers, including Samuel Morse, Alexander Bain,
Royal Earl House Royal Earl House (9 September 181425 February 1895) was the inventor of the first printing telegraph, which is now kept in the Smithsonian Institution. His nephew Henry Alonzo House is also a noted early American inventor. Royal Earl House spen ...
, David Edward Hughes,
Emile Baudot Emil or Emile may refer to: Literature *''Emile, or On Education'' (1762), a treatise on education by Jean-Jacques Rousseau * ''Émile'' (novel) (1827), an autobiographical novel based on Émile de Girardin's early life *''Emil and the Detective ...
, Donald Murray,
Charles L. Krum Charles L. Krum was a key figure in the development of the teleprinter, a machine which played a key role in the history of telegraphy and computing. In 1902, electrical engineer Mr. Frank Pearne approached Mr. Joy Morton, head of Morton Salt, see ...
,
Edward Kleinschmidt Edward Ernst Kleinschmidt (September 9, 1876 – August 22, 1977) was one of the inventors of the teleprinter, and was a prolific inventor who obtained 118 patents in the course of his 101-year life. Career Born in Bremen, Germany, in 1876, Klein ...
and
Frederick G. Creed Frederick George Creed (6 October 1871 – 11 December 1957) was a Canadian inventor, who spent most of his adult life in Britain. He worked in the field of telecommunications, and is particularly remembered as a key figure in the development of the ...
. Teleprinters were invented in order to send and receive messages without the need for operators trained in the use of Morse code. A system of two teleprinters, with one operator trained to use a keyboard, replaced two trained Morse code operators. The teleprinter system improved message speed and delivery time, making it possible for messages to be flashed across a country with little manual intervention. There were a number of parallel developments on both sides of the Atlantic Ocean. In 1835 Samuel Morse devised a recording telegraph, and
Morse code Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code is named after Samuel Morse, one ...
was born. Morse's instrument used a current to displace the armature of an electromagnet, which moved a marker, therefore recording the breaks in the current. Cooke & Wheatstone received a British patent covering telegraphy in 1837 and a second one in 1840 which described a type-printing telegraph with steel type fixed at the tips of petals of a rotating brass daisy-wheel, struck by an “electric hammer” to print Roman letters through carbon paper onto a moving paper tape. In 1841 Alexander Bain devised an electromagnetic printing telegraph machine. It used pulses of electricity created by rotating a dial over contact points to release and stop a type-wheel turned by weight-driven clockwork; a second clockwork mechanism rotated a drum covered with a sheet of paper and moved it slowly upwards so that the type-wheel printed its signals in a spiral. The critical issue was to have the sending and receiving elements working synchronously. Bain attempted to achieve this using
centrifugal governor A centrifugal governor is a specific type of governor with a feedback system that controls the speed of an engine by regulating the flow of fuel or working fluid, so as to maintain a near-constant speed. It uses the principle of proportional cont ...
s to closely regulate the speed of the clockwork. It was patented, along with other devices, on April 21, 1841. By 1846, the
Morse Morse may refer to: People * Morse (surname) * Morse Goodman (1917-1993), Anglican Bishop of Calgary, Canada * Morse Robb (1902–1992), Canadian inventor and entrepreneur Geography Antarctica * Cape Morse, Wilkes Land * Mount Morse, Churc ...
telegraph service was operational between Washington, D.C., and New York.
Royal Earl House Royal Earl House (9 September 181425 February 1895) was the inventor of the first printing telegraph, which is now kept in the Smithsonian Institution. His nephew Henry Alonzo House is also a noted early American inventor. Royal Earl House spen ...
patented his printing telegraph that same year. He linked two 28-key piano-style keyboards by wire. Each piano key represented a letter of the alphabet and when pressed caused the corresponding letter to print at the receiving end. A "shift" key gave each main key two optional values. A 56-character typewheel at the sending end was synchronised to coincide with a similar wheel at the receiving end. If the key corresponding to a particular character was pressed at the home station, it actuated the typewheel at the distant station just as the same character moved into the printing position, in a way similar to the (much later)
daisy wheel printer Daisy wheel printing is an impact printing technology invented in 1970 by Andrew Gabor at Diablo Data Systems. It uses interchangeable pre-formed type elements, each with typically 96 glyphs, to generate high-quality output comparable to pr ...
. It was thus an example of a synchronous data transmission system. House's equipment could transmit around 40 instantly readable words per minute, but was difficult to manufacture in bulk. The printer could copy and print out up to 2,000 words per hour. This invention was first put in operation and exhibited at the Mechanics Institute in New York in 1844. Landline teleprinter operations began in 1849, when a circuit was put in service between Philadelphia and New York City. In 1855, David Edward Hughes introduced an improved machine built on the work of Royal Earl House. In less than two years, a number of small telegraph companies, including Western Union in early stages of development, united to form one large corporation – Western Union Telegraph Co. – to carry on the business of telegraphy on the Hughes system. In France,
Émile Baudot Jean-Maurice-Émile Baudot (; 11 September 1845 – 28 March 1903), French telegraph engineer and inventor of the first means of digital communication Baudot code, was one of the pioneers of telecommunications. He invented a multiplexed print ...
designed in 1874 a system using a five-unit code, which began to be used extensively in that country from 1877. The British Post Office adopted the Baudot system for use on a simplex circuit between London and Paris in 1897, and subsequently made considerable use of duplex Baudot systems on their Inland Telegraph Services. During 1901, Baudot's code was modified by Donald Murray (1865–1945, originally from New Zealand), prompted by his development of a typewriter-like keyboard. The Murray system employed an intermediate step, a keyboard perforator, which allowed an operator to punch a
paper tape Five- and eight-hole punched paper tape 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 ...
, and a tape transmitter for sending the message from the punched tape. At the receiving end of the line, a printing mechanism would print on a paper tape, and/or a reperforator could be used to make a perforated copy of the message. As there was no longer a direct correlation between the operator's hand movement and the bits transmitted, there was no concern about arranging the code to minimize operator fatigue, and instead Murray designed the code to minimize wear on the machinery, assigning the code combinations with the fewest punched holes to the most frequently used characters. The Murray code also introduced what became known as "format effectors" or "
control character In computing and telecommunication, a control character or non-printing character (NPC) is a code point (a number) in a character set, that does not represent a written symbol. They are used as in-band signaling to cause effects other than t ...
s" – the CR (Carriage Return) and LF (Line Feed) codes. A few of Baudot's codes moved to the positions where they have stayed ever since: the NULL or BLANK and the DEL code. NULL/BLANK was used as an idle code for when no messages were being sent. In the United States in 1902, electrical engineer Frank Pearne approached Joy Morton, head of Morton Salt, seeking a sponsor for research into the practicalities of developing a printing telegraph system. Joy Morton needed to determine whether this was worthwhile and so consulted mechanical engineer
Charles L. Krum Charles L. Krum was a key figure in the development of the teleprinter, a machine which played a key role in the history of telegraphy and computing. In 1902, electrical engineer Mr. Frank Pearne approached Mr. Joy Morton, head of Morton Salt, see ...
, who was vice president of the Western Cold Storage Company. Krum was interested in helping Pearne, so space was set up in a laboratory in the attic of Western Cold Storage. Frank Pearne lost interest in the project after a year and left to get involved in teaching. Krum was prepared to continue Pearne’s work, and in August, 1903 a patent was filed for a 'typebar page printer'. In 1904, Krum filed a patent for a 'type wheel printing telegraph machine' which was issued in August, 1907. In 1906 Charles Krum's son, Howard Krum, joined his father in this work. It was Howard who developed and patented the start-stop synchronizing method for code telegraph systems, which made possible the practical teleprinter. In 1908, a working teleprinter was produced by the Morkrum Company (formed between Joy Morton and Charles Krum), called the Morkrum Printing Telegraph, which was field tested with the Alton Railroad. In 1910, the Morkrum Company designed and installed the first commercial teletypewriter system on Postal Telegraph Company lines between Boston and New York City using the "Blue Code Version" of the Morkrum Printing Telegraph. In 1916,
Edward Kleinschmidt Edward Ernst Kleinschmidt (September 9, 1876 – August 22, 1977) was one of the inventors of the teleprinter, and was a prolific inventor who obtained 118 patents in the course of his 101-year life. Career Born in Bremen, Germany, in 1876, Klein ...
filed a patent application for a typebar page printer. In 1919, shortly after the
Morkrum Joy Sterling Morton (September 27, 1855 – May 10, 1934) was an American businessman and entrepreneur best known for founding Morton Salt and establishing the Morton Arboretum in Lisle, Illinois. Biography He was born on September 27, 1855 in D ...
company obtained their patent for a start-stop synchronizing method for code telegraph systems, which made possible the practical teleprinter, Kleinschmidt filed an application titled "Method of and Apparatus for Operating Printing Telegraphs" which included an improved start-stop method. The basic start-stop procedure, however, is much older than the Kleinschmidt and Morkrum inventions. It was already proposed by D'Arlincourt in 1870. Instead of wasting time and money in patent disputes on the start-stop method, Kleinschmidt and the Morkrum Company decided to merge and form the
Morkrum-Kleinschmidt 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. ...
Company in 1924. The new company combined the best features of both their machines into a new typewheel printer for which Kleinschmidt, Howard Krum, and Sterling Morton jointly obtained a patent. In 1924 Britain's
Creed & Company Creed & Company was a British telecommunications company founded by Frederick George Creed which was an important pioneer in the field of teleprinter machines. It was merged into the International Telephone and Telegraph Corporation (ITT) in ...
, founded by
Frederick G. Creed Frederick George Creed (6 October 1871 – 11 December 1957) was a Canadian inventor, who spent most of his adult life in Britain. He worked in the field of telecommunications, and is particularly remembered as a key figure in the development of the ...
, entered the teleprinter field with their Model 1P, a page printer, which was soon superseded by the improved Model 2P. In 1925 Creed acquired the patents for Donald Murray's Murray code, a rationalised Baudot code. The Model 3 tape printer, Creed’s first combined start-stop machine, was introduced in 1927 for the Post Office telegram service. This machine printed received messages directly on to gummed paper tape at a rate of 65 words per minute. Creed created his first keyboard perforator, which used compressed air to punch the holes. He also created a reperforator (receiving perforator) and a printer. The reperforator punched incoming Morse signals on to paper tape and the printer decoded this tape to produce alphanumeric characters on plain paper. This was the origin of the Creed High Speed Automatic Printing System, which could run at an unprecedented 200 words per minute. His system was adopted by the Daily Mail for daily transmission of the newspaper's contents. The Creed Model 7 page printing teleprinter was introduced in 1931 and was used for the inland Telex service. It worked at a speed of 50 baud, about 66 words a minute, using a code based on the Murray code. A teleprinter system was installed in the
Bureau of Lighthouses The United States Lighthouse Service, also known as the Bureau of Lighthouses, was the agency of the United States Government and the general lighthouse authority for the United States from the time of its creation in 1910 as the successor of the ...
, Airways Division, Flight Service Station Airway Radio Stations system in 1928, carrying administrative messages, flight information and weather reports. By 1938, the teleprinter network, handling weather traffic, extended over 20,000 miles, covering all 48 states except Maine, New Hampshire, and South Dakota.


Ways in which teleprinters were used

There were at least five major types of teleprinter networks: * Exchange systems such as Telex and TWX created a real-time circuit between two machines, so that anything typed on one machine appeared at the other end immediately. US and UK systems had telephone dials, and prior to 1981 five North American Numbering Plan (NANPA)
area codes A telephone numbering plan is a type of numbering scheme used in telecommunication to assign telephone numbers to subscriber telephones or other telephony endpoints. Telephone numbers are the addresses of participants in a telephone network, reac ...
were reserved for teleprinter use. German systems did "dialing" via the keyboard. Typed "chat" was possible, but because billing was by connect time, it was common to prepare messages in advance on
paper tape Five- and eight-hole punched paper tape 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 ...
and transmit them without pauses for typing. *
Leased line A leased line is a private telecommunications circuit between two or more locations provided according to a commercial contract. It is sometimes also known as a private circuit, and as a data line in the UK. Typically, leased lines are used by ...
and
radioteletype Radioteletype (RTTY) is a telecommunications system consisting originally of two or more electromechanical teleprinters in different locations connected by radio rather than a wired link. Radioteletype evolved from earlier landline teleprinter o ...
networks arranged in point-to-point and / or multipoint configurations supported
data processing Data processing is the collection and manipulation of digital data to produce meaningful information. Data processing is a form of ''information processing'', which is the modification (processing) of information in any manner detectable by a ...
applications for government and industry, such as integrating the accounting, billing, management, production, purchasing, sales, shipping and receiving departments within an organization to speed internal communications. * Message switching systems were an early form of E-mail, using electromechanical equipment. See
Telegram Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas p ...
, Western Union,
Plan 55-A Plan 55-A was one in a series of store and forward message switching systems developed by Western Union and used from 1948 to 1976 for processing telegrams. It is an automated successor to Plan 51, which commenced service in 1951 in a nationwide ne ...
. Military organizations had similar but separate systems, such as Autodin. * Broadcast systems such as weather information distribution and "news wires", which were received on "wire machines". Examples were operated by Associated Press,
National Weather Service The National Weather Service (NWS) is an agency of the United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weather-related products to organizations and the public for the ...
, Reuters, and United Press (later
UPI United Press International (UPI) is an American international news agency whose newswires, photo, news film, and audio services provided news material to thousands of newspapers, magazines, radio and television stations for most of the 20th c ...
). Information was printed on receive-only teleprinters, without keyboards or dials. * "Loop" systems, where anything typed on any machine on the loop printed on all the machines. American police departments used such systems to interconnect precincts.


Teleprinter operation

Most teleprinters used the 5-
bit The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represented ...
International Telegraph Alphabet No. 2 (ITA2). This limited the character set to 32 codes (25 = 32). One had to use a "FIGS" (for "figures") shift key to type numbers and special characters. Special versions of teleprinters had FIGS characters for specific applications, such as weather symbols for weather reports. Print quality was poor by modern standards. The ITA2 code was used asynchronously with start and stop bits: the asynchronous code design was intimately linked with the start-stop electro-mechanical design of teleprinters. (Early systems had used synchronous codes, but were hard to synchronize mechanically). Other codes, such as FIELDATA and
Flexowriter The Friden Flexowriter produced by the Friden Calculating Machine Company, 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 atta ...
, were introduced but never became as popular as ITA2. ''Mark'' and ''space'' are terms describing
logic level In digital circuits, a logic level is one of a finite number of states that a digital signal can inhabit. Logic levels are usually represented by the voltage difference between the signal and ground, although other standards exist. The range ...
s in teleprinter circuits. The native mode of communication for a teleprinter is a simple series DC circuit that is interrupted, much as a rotary dial interrupts a telephone signal. The marking condition is when the circuit is closed (current is flowing), the spacing condition is when the circuit is open (no current is flowing). The "idle" condition of the circuit is a continuous marking state, with the start of a character signalled by a "start bit", which is always a space. Following the start bit, the character is represented by a fixed number of bits, such as 5 bits in the ITA2 code, each either a mark or a space to denote the specific character or machine function. After the character's bits, the sending machine sends one or more stop bits. The stop bits are marking, so as to be distinct from the subsequent start bit. If the sender has nothing more to send, the line simply remains in the marking state (as if a continuing series of stop bits) until a later space denotes the start of the next character. The time between characters need not be an integral multiple of a bit time, but it must be at least the minimum number of stop bits required by the receiving machine. When the line is broken, the continuous spacing (open circuit, no current flowing) causes a receiving teleprinter to cycle continuously, even in the absence of stop bits. It prints nothing because the characters received are all zeros, the ITA2 blank (or
ASCII 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. Because of ...
)
null character The null character (also null terminator) is a control character with the value zero. It is present in many character sets, including those defined by the Baudot and ITA2 codes, ISO/IEC 646 (or ASCII), the C0 control code, the Universal Coded Ch ...
. Teleprinter circuits were generally leased from a communications
common carrier A common carrier in common law countries (corresponding to a public carrier in some civil law systems,Encyclopædia Britannica CD 2000 "Civil-law public carrier" from "carriage of goods" usually called simply a ''carrier'') is a person or compan ...
and consisted of ordinary
telephone cable A telephone line or telephone circuit (or just line or circuit industrywide) is a single-user circuit on a telephone communication system. It is designed to reproduce speech of a quality that is understandable. It is the physical wire or ot ...
s that extended from the teleprinter located at the customer location to the common carrier central office. These teleprinter circuits were connected to switching equipment at the central office for Telex and TWX service.
Private line In telecommunication, a private line is typically a telephone company service that uses a dedicated, usually unswitched point-to-point circuit, but it may involve private switching arrangements, or predefined transmission physical or virtual pat ...
teleprinter circuits were not directly connected to switching equipment. Instead, these private line circuits were connected to
network hub In network science, a hub is a node with a number of links that greatly exceeds the average. Emergence of hubs is a consequence of a scale-free property of networks. While hubs cannot be observed in a random network, they are expected to emerge i ...
s and repeaters configured to provide point to point or point to multipoint service. More than two teleprinters could be connected to the same wire circuit by means of a
current loop In electrical signalling an analog current loop is used where a device must be monitored or controlled remotely over a pair of conductors. Only one current level can be present at any time. A major application of current loops is the industry d ...
. Earlier teleprinters had three rows of keys and only supported upper case letters. They used the 5 bit ITA2 code and generally worked at 60 to 100 words per minute. Later teleprinters, specifically the Teletype Model 33, used ASCII code, an innovation that came into widespread use in the 1960s as computers became more widely available. "Speed", intended to be roughly comparable to
words per minute Words per minute, commonly abbreviated wpm (sometimes uppercased WPM), is a measure of words processed in a minute, often used as a measurement of the speed of typing, reading or Morse code sending and receiving. Alphanumeric entry Since words ...
, is the standard term introduced by Western Union for a mechanical teleprinter data transmission rate using the 5-bit ITA2 code that was popular in the 1940s and for several decades thereafter. Such a machine would send 1 start bit, 5 data bits, and 1.42 stop bits. This unusual stop bit time is actually a rest period to allow the mechanical printing mechanism to synchronize in the event that a garbled signal is received. This is true especially on
high frequency High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten ...
radio circuits where selective fading is present. Selective fading causes the mark signal amplitude to be randomly different from the space signal amplitude. Selective fading, or Rayleigh fading can cause two carriers to randomly and independently fade to different depths. Since modern computer equipment cannot easily generate 1.42 bits for the stop period, common practice is to either approximate this with 1.5 bits, or to send 2.0 bits while accepting 1.0 bits receiving. For example, a "60 speed" machine is geared at 45.5
baud In telecommunication and electronics, baud (; symbol: Bd) is a common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel. It is the unit for symbol rate or modulation ...
(22.0 ms per bit), a "66 speed" machine is geared at 50.0
baud In telecommunication and electronics, baud (; symbol: Bd) is a common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel. It is the unit for symbol rate or modulation ...
(20.0 ms per bit), a "75 speed" machine is geared at 56.9 baud (17.5 ms per bit), a "100 speed" machine is geared at 74.2 baud (13.5 ms per bit), and a "133 speed" machine is geared at 100.0 baud (10.0 ms per bit). 60 speed became the ''de facto'' standard for
amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency communica ...
RTTY operation because of the widespread availability of equipment at that speed and the U.S. Federal Communications Commission (FCC) restrictions to only 60 speed from 1953 to 1972. Telex,
news agency A news agency is an organization that gathers news reports and sells them to subscribing news organizations, such as newspapers, magazines and radio and television broadcasters. A news agency may also be referred to as a wire service, newswire ...
wires and similar services commonly used 66 speed services. There was some migration to 75 and 100 speed as more reliable devices were introduced. However, the limitations of HF transmission such as excessive error rates due to multipath distortion and the nature of ionospheric propagation kept many users at 60 and 66 speed. Most audio recordings in existence today are of teleprinters operating at 60 words per minute, and mostly of the Teletype Model 15. Another measure of the speed of a teletypewriter was in total "operations per minute (OPM)". For example, 60 speed was usually 368 OPM, 66 speed was 404 OPM, 75 speed was 460 OPM, and 100 speed was 600 OPM. Western Union Telexes were usually set at 390 OPM, with 7.0 total bits instead of the customary 7.42 bits. Both wire-service and private teleprinters had bells to signal important incoming messages and could ring 24/7 while the power was turned on. For example, ringing 4 bells on UPI wire-service machines meant an "Urgent" message; 5 bells was a "Bulletin"; and 10 bells was a FLASH, used only for very important news, such as the
assassination of John F. Kennedy John F. Kennedy, the 35th president of the United States, was assassinated on Friday, November 22, 1963, at 12:30 p.m. CST in Dallas, Texas, while riding in a presidential motorcade through Dealey Plaza. Kennedy was in the vehicle wi ...
. The teleprinter circuit was often linked to a 5-bit
paper tape Five- and eight-hole punched paper tape 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 ...
punch (or "reperforator") and reader, allowing messages received to be resent on another circuit. Complex military and commercial communications networks were built using this technology. Message centers had rows of teleprinters and large racks for paper tapes awaiting transmission. Skilled operators could read the priority code from the hole pattern and might even feed a "FLASH PRIORITY" tape into a reader while it was still coming out of the punch. Routine traffic often had to wait hours for relay. Many teleprinters had built-in paper tape readers and punches, allowing messages to be saved in machine-readable form and edited
off-line In computer technology and telecommunications, online indicates a state of connectivity and offline indicates a disconnected state. In modern terminology, this usually refers to an Internet connection, but (especially when expressed "on line" or ...
. Communication by radio, known as ''
radioteletype Radioteletype (RTTY) is a telecommunications system consisting originally of two or more electromechanical teleprinters in different locations connected by radio rather than a wired link. Radioteletype evolved from earlier landline teleprinter o ...
'' or ''RTTY'' (pronounced ''ritty''), was also common, especially among military users. Ships, command posts (mobile, stationary, and even airborne) and logistics units took advantage of the ability of operators to send reliable and accurate information with a minimum of training.
Amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency communica ...
operators continue to use this mode of communication today, though most use computer-interface sound generators, rather than legacy hardware teleprinter equipment. Numerous modes are in use within the "ham radio" community, from the original ITA2 format to more modern, faster modes, which include error-checking of characters.


Control characters

A typewriter or electromechanical printer can print characters on paper, and execute operations such as move the carriage back to the left margin of the same line (
carriage return A carriage return, sometimes known as a cartridge return and often shortened to CR, or return, is a control character or mechanism used to reset a device's position to the beginning of a line of text. It is closely associated with the line feed ...
), advance to the same column of the next line (
line feed Newline (frequently called line ending, end of line (EOL), next line (NEL) or line break) is a control character or sequence of control characters in character encoding specifications such as ASCII, EBCDIC, Unicode, etc. This character, or a ...
), and so on. Commands to control non-printing operations were transmitted in exactly the same way as printable characters by sending control characters with defined functions (e.g., the ''line feed'' character forced the carriage to move to the same position on the next line) to teleprinters. In modern computing and communications a few control characters, such as carriage return and line feed, have retained their original functions (although they are often implemented in software rather than activating electromechanical mechanisms to move a physical printer carriage) but many others are no longer required and are used for other purposes.


Answer back mechanism

Some teleprinters had a "Here is" key, which transmitted a fixed sequence of 20 or 22 characters, programmable by breaking tabs off a drum. This sequence could also be transmitted automatically upon receipt of an ENQ (control E) signal, if enabled. This was commonly used to identify a station; the operator could press the key to send the station identifier to the other end, or the remote station could trigger its transmission by sending the ENQ character, essentially asking "who are you?"


Manufacturers


Creed & Company

British
Creed & Company Creed & Company was a British telecommunications company founded by Frederick George Creed which was an important pioneer in the field of teleprinter machines. It was merged into the International Telephone and Telegraph Corporation (ITT) in ...
built teleprinters for the GPO's teleprinter service. * Creed model 7 (page printing teleprinter introduced in 1931) * Creed model 7B (50 baud page printing teleprinter) * Creed model 7E (page printing teleprinter with overlap cam and range finder) * Creed model 7/TR (non-printing teleprinter reperforator) * Creed model 54 (page printing teleprinter introduced in 1954) * Creed model 75 (page printing teleprinter introduced in 1958) * Creed model 85 (printing reperforator introduced in 1948) * Creed model 86 (printing reperforator using 7/8" wide tape) * Creed model 444 (page printing teleprinter introduced in 1966, GPO type 15)


Gretag

The Gretag ETK-47 teleprinter developed in Switzerland by
Edgar Gretener Edgar Gretener (2 March 1902 in Lucerne – 21 October 1958 in Zurich) was a Swiss electrical engineer. Gretener was the twelfth of 14 siblings. He studied electrical engineering at Swiss Federal Institute of Technology (ETH Zurich), where he r ...
in 1947 uses a 14-bit
start-stop transmission Asynchronous serial communication is a form of serial communication in which the communicating endpoints' interfaces are not continuously synchronized by a common clock signal. Instead of a common synchronization signal, the data stream contai ...
method similar to the 5-bit code used by other teleprinters. However, instead of a more-or-less arbitrary mapping between 5-bit codes and letters in the Latin alphabet, all characters (letters, digits, and punctuation) printed by the ETK are built from 14 basic elements on a print head, very similar to the 14 elements on a modern
fourteen-segment display A fourteen-segment display (FSD) (sometimes referred to as a starburst display or Union Jack display) is a type of display based on 14 segments that can be turned on or off to produce letters and numerals. It is an expansion of the more com ...
, each one selected independently by one of the 14 bits during transmission. Because it does not use a fixed character set, but instead builds up characters from smaller elements, the ETK printing element does not require modification to switch between Latin, Cyrillic, and Greek characters.


Kleinschmidt Labs

In 1931, American inventor Edward Kleinschmidt formed Kleinschmidt Labs to pursue a different design of teleprinter. In 1944 Kleinschmidt demonstrated their lightweight unit to the Signal Corps and in 1949 their design was adopted for the Army's portable needs. In 1956, Kleinschmidt Labs merged with
Smith-Corona Smith Corona is an American manufacturer of thermal labels, direct thermal labels, and thermal ribbons used in warehouses for primarily barcode labels. Once a large U.S. typewriter and mechanical calculator manufacturer, it expanded aggressively ...
, which then merged with the Marchant Calculating Machine Co., forming the SCM Corporation. By 1979, the Kleinschmidt division was turning to Electronic Data Interchange and away from mechanical products. Kleinschmidt machines, with the military as their primary customer, used standard military designations for their machines. The teleprinter was identified with designations such as a TT-4/FG, while communication "sets" to which a teleprinter might be a part generally used the standard Army/Navy designation system such as AN/FGC-25. This includes Kleinschmidt teleprinter TT-117/FG and tape reperforator TT-179/FG.


Morkrum

Morkrum Joy Sterling Morton (September 27, 1855 – May 10, 1934) was an American businessman and entrepreneur best known for founding Morton Salt and establishing the Morton Arboretum in Lisle, Illinois. Biography He was born on September 27, 1855 in D ...
made their first commercial installation of a printing telegraph with the Postal Telegraph Company in Boston and New York in 1910. It became popular with railroads, and the Associated Press adopted it in 1914 for their
wire service A news agency is an organization that gathers news reports and sells them to subscribing news organizations, such as newspapers, magazines and radio and television broadcasters. A news agency may also be referred to as a wire service, newswire ...
. Morkrum merged with their competitor Kleinschmidt Electric Company to become Morkrum-Kleinschmidt Corporation shortly before being renamed the Teletype Corporation.


Olivetti

Italian office equipment maker Olivetti (est. 1908) started to manufacture teleprinters in order to provide Italian post offices with modern equipment to send and receive telegrams. The first models typed on a paper ribbon, which was then cut and glued into telegram forms. * Olivetti T1 (1938–1948) * Olivetti T2 (1948–1968) * Olivetti Te300 (1968–1975) * Olivetti Te400 (1975–1991)


Siemens & Halske

Siemens & Halske, later Siemens AG, a German company, founded in 1897. * Teleprinter Model 100 Ser 1 (end of the 1950s) – Used for Telex service * Teleprinter Model 100 Ser. 11 – Later version with minor changes * Teleprinter Model T100 ND (single current) NDL (double current) models * Teleprinter Model T 150 (electromechanical) * Offline tape punch for creating messages * Teleprinter T 1000 electronic teleprinter (processor based) 50-75-100 Bd. Tape punch and reader attachments ND/NDL/SEU V21modem model * Teleprinter T 1000 Receive only units as used by newsrooms for unedited SAPA/Reuters/AP feeds etc. * Teleprinter T 1200 electronic teleprinter (processor based) 50-75-100-200 Bd.Green LED text display, 1.44M 3.5" floppy disk ("stiffy") attachment * PC-Telex Teleprinter with dedicated dot matrix printer Connected to IBM compatible PC (as used by Telkom South Africa) * T4200 Teletex Teleprinter With two floppy disc drives and black and white monitor/daisy wheel typewriter (DOS2)


Teletype Corporation

The Teletype Corporation, a part of
American Telephone and Telegraph Company AT&T Inc. is an American multinational telecommunications holding company headquartered at Whitacre Tower in Downtown Dallas, Texas. It is the world's largest telecommunications company by revenue and the third largest provider of mobile tel ...
's Western Electric manufacturing arm since 1930, was founded in 1906 as the Morkrum Company. In 1925, a merger between Morkrum and Kleinschmidt Electric Company created the Morkrum-Kleinschmidt Company. The name was changed in December 1928 to Teletype Corporation. In 1930, Teletype Corporation was purchased by the
American Telephone and Telegraph Company AT&T Inc. is an American multinational telecommunications holding company headquartered at Whitacre Tower in Downtown Dallas, Texas. It is the world's largest telecommunications company by revenue and the third largest provider of mobile tel ...
and became a subsidiary of Western Electric. In 1984, the divestiture of the Bell System resulted in the Teletype name and logo being replaced by the AT&T name and logo, eventually resulting in the brand being extinguished. The last vestiges of what had been the Teletype Corporation ceased in 1990, bringing to a close the dedicated teleprinter business. Despite its long-lasting trademark status, the word ''Teletype'' went into common generic usage in the news and telecommunications industries. Records of the United States Patent and Trademark Office indicate the trademark has expired and is considered dead. Teletype machines tended to be large, heavy, and extremely robust, capable of running non-stop for months at a time if properly lubricated. The Model 15 stands out as one of a few machines that remained in production for many years. It was introduced in 1930 and remained in production until 1963, a total of 33 years of continuous production. Very few complex machines can match that record. The production run was stretched somewhat by World War II—the Model 28 was scheduled to replace the Model 15 in the mid-1940s, but Teletype built so many factories to produce the Model 15 during World War II, it was more economical to continue mass production of the Model 15. The Model 15, in its receive only, no keyboard, version was the classic "news Teletype" for decades. * Model 15 = Baudot version, 45 Baud, optional tape punch and reader * Model 28 = Baudot version, 45-50-56-75 Baud, optional tape punch and reader * Model 32 = small lightweight machine (cheap production) 45-50-56-75 Baud, optional tape punch and reader * Model 33 = same as Model 32 but for 8 level ASCII-plus-parity-bit, used as computer terminal, optional tape punch and reader * Model 35 = same as Model 28 but for 8 level ASCII-plus-parity-bit, used as heavy-duty computer terminal, optional tape punch and reader * Model 37 = improved version of the Model 35, higher speeds up to 150 Baud, optional tape punch and reader * Model 38 = similar to Model 33, but for 132 char./line paper (14 inches wide), optional tape punch and reader * Model 40 = new system processor based, w/ monitor screen, but mechanical "chain printer" * Model 42 = new cheap production Baudot machine to replace Model 28 and Model 32, paper tape acc. * Model 43 = same but for 8 level ASCII-plus-parity-bit, to replace Model 33 and Model 35, paper tape acc. Several different high-speed printers like the "Ink-tronic" etc.


Texas Instruments

Texas Instruments developed its own line of teletypes in 1971, the Silent 700. Their name came from the use of a
thermal printer Thermal printing (or direct thermal printing) is a digital printing process which produces a printed image by passing paper with a thermochromic coating, commonly known as thermal paper, over a print head consisting of tiny electrically heated ...
head to emit copy, making them substantially quieter than contemporary teletypes using
impact printing In computing, a printer is a peripheral machine which makes a persistent representation of graphics or text, usually on paper. While most output is human-readable, bar code printers are an example of an expanded use for printers. Differ ...
, and some such as the 1975 Model 745 and 1983 Model 707 were even small enough to be sold as portable units. Certain models came with
acoustic coupler In telecommunications, an acoustic coupler is an interface device for coupling electrical signals by acoustical means—usually into and out of a telephone. The link is achieved through converting electric signals from the phone line to sound a ...
s and some had internal storage, initially
cassette tape The Compact Cassette or Musicassette (MC), also commonly called the tape cassette, cassette tape, audio cassette, or simply tape or cassette, is an analog magnetic tape recording format for audio recording and playback. Invented by Lou Otten ...
in the 1973 Models 732/733 ASR and later
bubble memory Bubble memory is a type of non-volatile computer memory that uses a thin film of a magnetic material to hold small magnetized areas, known as ''bubbles'' or ''domains'', each storing one bit of data. The material is arranged to form a series of ...
in the 1977 Models 763/765, the first and one of the few commercial products to use the technology. In these units their storage capability essentially acted as a form of punched tape. The last Silent 700 was the 1987 700/1200 BPS, which was sold into the early 1990s.


Telex

A global teleprinter network called '' Telex'' was developed in the late 1920s, and was used through most of the 20th century for business communications. The main difference from a standard teleprinter is that Telex includes a switched routing network, originally based on pulse-telephone dialing, which in the United States was provided by Western Union. AT&T developed a competing network called " TWX" which initially also used rotary dialing and Baudot code, carried to the customer premises as pulses of DC on a metallic copper pair. TWX later added a second ASCII-based service using
Bell 103 The Bell 103 modem or Bell 103 dataset was the second commercial modem for computers, released by AT&T Corporation in 1962. It allowed digital data to be transmitted over regular unconditioned telephone lines at a speed of 300 bits per second. I ...
type modems served over lines whose physical interface was identical to regular telephone lines. In many cases, the TWX service was provided by the same telephone central office that handled voice calls, using
class of service Class of service (COS or CoS) is a parameter used in data and voice protocols to differentiate the types of payloads contained in the packet being transmitted. The objective of such differentiation is generally associated with assigning prioritie ...
to prevent POTS customers from connecting to TWX customers. Telex is still in use in some countries for certain applications such as shipping, news, weather reporting and military command. Many business applications have moved to the Internet as most countries have discontinued telex/TWX services.


Teletypesetter

In addition to the 5-bit Baudot code and the much later seven-bit ASCII code, there was a six-bit code known as the Teletypesetter code (TTS) used by news wire services. It was first demonstrated in 1928 and began to see widespread use in the 1950s. Through the use of "shift in" and "shift out" codes, this six-bit code could represent a full set of upper and lower case characters, digits, symbols commonly used in newspapers, and typesetting instructions such as "flush left" or "center", and even "auxiliary font", to switch to italics or bold type, and back to roman ("upper rail"). The TTS produces aligned text, taking into consideration character widths and column width, or line length. A Model 20 Teletype machine with a paper tape punch ("reperforator") was installed at subscriber newspaper sites. Originally these machines would simply punch paper tapes and these tapes could be read by a tape reader attached to a "Teletypesetter operating unit" installed on a
Linotype machine The Linotype machine ( ) is a "line casting" machine used in printing; manufactured and sold by the former Mergenthaler Linotype Company and related It was a hot metal typesetting system that cast lines of metal type for individual uses. Lin ...
. The "operating unit" was essentially a tape reader which actuated a mechanical box, which in turn operated the Linotype's keyboard and other controls, in response to the codes read from the tape, thus creating type for printing in newspapers and magazines. This allowed higher production rates for the Linotype, and was used both locally, where the tape was first punched and then fed to the machine, as well as remotely, using tape transmitters and receivers. Remote use played an essential role for distributing identical content, such as Syndicated columns, News agency news,
Classified advertising Classified advertising is a form of advertising, particularly common in newspapers, online and other periodicals, which may be sold or distributed free of charge. Classified advertisements are much cheaper than larger display advertisements used ...
, and more, to different publications across wide geographical areas. In later years the incoming 6-bit current loop signal carrying the TTS code was connected to a minicomputer or
mainframe A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as censuses, industry and consumer statistics, enterprise ...
for storage, editing, and eventual feed to a phototypesetting machine.


Teleprinters in computing

Computers used teleprinters for input and output from the early days of computing.
Punched card A punched card (also punch card or punched-card) is a piece of stiff paper that holds digital data represented by the presence or absence of holes in predefined positions. Punched cards were once common in data processing applications or to di ...
readers and fast printers replaced teleprinters for most purposes, but teleprinters continued to be used as interactive time-sharing terminals until video
displays A display device is an output device for presentation of information in visual or tactile form (the latter used for example in tactile electronic displays for blind people). When the input information that is supplied has an electrical signal ...
became widely available in the late 1970s. Users typed commands after a prompt character was printed. Printing was unidirectional; if the user wanted to delete what had been typed, further characters were printed to indicate that previous text had been cancelled. When video displays first became available the user interface was initially exactly the same as for an electromechanical printer; expensive and scarce video terminals could be used interchangeably with teleprinters. This was the origin of the text terminal and the command-line interface.
Paper tape Five- and eight-hole punched paper tape 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 ...
was sometimes used to prepare input for the computer session off line and to capture computer output. The popular Teletype Model 33 used 7-bit
ASCII 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. Because of ...
code (with an eighth parity bit) instead of Baudot. The common modem communications settings, ''Start/Stop Bits'' and ''Parity,'' stem from the Teletype era. In early operating systems such as Digital's RT-11, serial communication lines were often connected to teleprinters and were given device names starting with . This and similar conventions were adopted by many other operating systems. Unix and Unix-like operating systems use the prefix , for example , or (for pseudo-tty), such as , but some of them (e.g. Solaris & recent Linux) have replaced pty files by a pts folder (where "pt" stands for "pseudoterminal" instead). In many computing contexts, "TTY" has become the name for any text terminal, such as an external
console Console may refer to: Computing and video games * System console, a physical device to operate a computer ** Virtual console, a user interface for multiple computer consoles on one device ** Command-line interface, a method of interacting with ...
device, a user dialing into the system on a modem on a serial port device, a printing or graphical computer terminal on a computer's serial port or the RS-232 port on a
USB Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply ( interfacing) between computers, peripherals and other computers. A broad ...
-to-RS-232 converter attached to a computer's USB port, or even a terminal emulator application in the window system using a
pseudoterminal In some operating systems, including Unix and Linux, a pseudoterminal, pseudotty, or PTY is a pair of pseudo-device endpoints (files) which establish asynchronous, bidirectional communication ( IPC) channel (with two ports) between two or more pr ...
device. Teleprinters were also used to record fault printout and other information in some TXE telephone exchanges.


Obsolescence of teleprinters

Although printing news, messages, and other text at a distance is still universal, the dedicated teleprinter tied to a pair of leased copper wires was made functionally obsolete by the
fax Fax (short for facsimile), sometimes called telecopying or telefax (the latter short for telefacsimile), is the telephonic transmission of scanned printed material (both text and images), normally to a telephone number connected to a printer o ...
, personal computer, inkjet printer, email, and the Internet. In the 1980s,
packet radio In digital radio, packet radio is the application of packet switching techniques to digital radio communications. Packet radio uses a packet switching protocol as opposed to circuit switching or message switching protocols to transmit digital da ...
became the most common form of digital communications used in amateur radio. Soon, advanced multimode electronic interfaces such as the AEA PK-232 were developed, which could send and receive not only packet, but various other modulation types including Baudot. This made it possible for a home or laptop computer to replace teleprinters, saving money, complexity, space and the massive amount of paper which mechanical machines used. As a result, by the mid-1990s, amateur use of actual teleprinters had waned, though a core of "purists" still operate on equipment originally manufactured in the 1940s, 1950s, 1960s and 1970s.


See also

*
Letter-quality printer A letter-quality printer was a form of computer impact printer that was able to print with the quality typically expected from a business typewriter such as an IBM Selectric. A letter-quality printer operates in much the same fashion as a typ ...
*
Plan 55-A Plan 55-A was one in a series of store and forward message switching systems developed by Western Union and used from 1948 to 1976 for processing telegrams. It is an automated successor to Plan 51, which commenced service in 1951 in a nationwide ne ...
, a message switching system for telegrams *
Radioteletype Radioteletype (RTTY) is a telecommunications system consisting originally of two or more electromechanical teleprinters in different locations connected by radio rather than a wired link. Radioteletype evolved from earlier landline teleprinter o ...
*
Siemens and Halske T52 The Siemens & Halske T52, also known as the Geheimschreiber ("secret teleprinter"), or ''Schlüsselfernschreibmaschine'' (SFM), was a World War II German cipher machine and teleprinter produced by the electrical engineering firm Siemens & Halske. T ...
– the ''Geheimfernschreiber'' (''secrets teleprinter'')


References


Further reading


"Teletype Messages Sent Through Switch Board"
'' Popular Mechanics'', April 1932. AT&T offering two way service through switchboards * * * on the role of the teleprinter code in WWII


External links


A first-hand report of Teletype Corporation's early years




by R.A. Nelson
"Some Notes on Teletype Corporation"

Mass.gov: TTY explanation and government best practices for TTY use


Patents

* "Telegraph printer" (Type 12 Teletype), filed June 1924, issued April 1928 * "Telegraph receiver" (Type 14 Teletype), filed December 1924, issued February 1930 * "Signalling system and apparatus therefor" (Type 15 Teletype) – filed July 1930, issued April 1933 * "Frequency-Shift Teletypewriter" – filed August 1966, issued April 1970 {{Authority control History of telecommunications Impact printing Telegraphy Typewriters