Editing Teleprinter

{{Short description|Device for transmitting messages in written form by electrical signals}}
{{Redirect|Teletype}}
{{For|the telecommunications system consisting of teleprinters connected by radio|Radioteletype}}
{{Use mdy dates|date=May 2012}}
[[File:WACsOperateTeletype.jpg|thumb|[[Teletype Corporation|Teletype]] teleprinters in use in England during [[World War II]]|alt=|250x250px]]
[[File:Dag Hammarskjöld - ASCII - teleprinter art -1962.jpg|thumb|Example of [[teleprinter art]]: a portrait of [[Dag Hammarskjöld]], 1962|alt=]]

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 (telecommunications)|point-to-point]] and [[point-to-multipoint communication|point-to-multipoint]] configurations. 

Initially, from 1887 at the earliest, teleprinters were used in [[telegraphy]].<ref>{{Citation |last=Nelson |first=R.A. |title=History Of Teletype Development |url=https://www.thocp.net/hardware/history_of_teletype_development_.htm |archive-url=https://web.archive.org/web/20201105231651/http://www.thocp.net/hardware/history_of_teletype_development_.htm |archive-date=2020-11-05 |url-status=dead}}</ref> [[Electrical telegraphy]] had been developed decades earlier in the late 1830s and 1840s,<ref>{{Citation |last=Roberts |first=Steven |author-link=Stephen Roberts (historian) |title=Distant Writing |url=http://distantwriting.co.uk/index.htm}}</ref> then using simpler [[Morse key]] equipment and [[telegraph operator]]s. The introduction of teleprinters automated much of this work and eventually largely replaced [[skilled labour|skilled]] operators versed in [[Morse code]] with [[Data entry clerk|typist]]s and machines communicating faster via [[Baudot code]].

With the development of early [[computers]] in the 1950s,<ref>{{better source|date=January 2024}} {{cite web |url=https://history-computer.com/keyboard-history-of-the-modern-computer-keyboard/ |title=History of the Modern Computer Keyboard |date=January 4, 2021 |access-date=2021-05-23 |archive-url=https://web.archive.org/web/20210302191307/https://history-computer.com/keyboard-history-of-the-modern-computer-keyboard/ |archive-date=2021-03-02 |quote="In 1954 at MIT, researchers [began] experimenting with direct keyboard input to computers. Until then, computer users fed their programs into a computer using punched cards or paper tape. Douglas Ross… believed… a [[Flexowriter]] [teletypewriter]… could function as a keyboard input device… Thus in 1955 MIT’s [[Whirlwind I|Whirlwind]] [became] the first computer in the world to allow its users to enter commands through a keyboard…"}}</ref> teleprinters were adapted to allow typed data to be sent to a computer, and responses printed. Some teleprinter models could also be used to create [[punched tape]] for [[Computer data storage|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. A teleprinter attached to a [[modem]] could also communicate through [[telephone line]]s. 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 terminal]]s which typically have a [[computer monitor]] 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 [[Aeronautical Fixed Telecommunication Network|AFTN]] and [[airline teletype system]]),<ref name=":0">{{Cite journal |last=Latifiyan |first=Pouya |date=Winter 2021 |title=Aeronautical Fixed Telecommunication network and surrounding technologies |journal=Take off |publisher=[[Civil Aviation Technology College]] |volume=2}}</ref> and variants called [[Telecommunications device for the deaf|Telecommunications Devices for the Deaf]] (TDDs) are used by the [[hearing loss|hearing impaired]] for typed communications over ordinary telephone lines.

==History==
{{Organize section|date=March 2024|reason=it could be more easily read if subdivided by principle of operation}}
The teleprinter evolved through a series of inventions by a number of engineers, including [[Samuel Morse]], [[Alexander Bain (inventor)|Alexander Bain]], [[Royal Earl House]], [[David Edward Hughes]], [[Emile Baudot]], [[Donald Murray (inventor)|Donald Murray]], [[Charles L. Krum]], [[Edward Kleinschmidt]] and [[Frederick G. Creed]]. 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.<ref name="query.nytimes.com">{{Citation |title=Typewriter May Soon Be Transmitter of Telegrams |newspaper=[[The New York Times]] |date=January 25, 1914 |url=https://timesmachine.nytimes.com/timesmachine/1914/01/25/100081424.pdf}}</ref>

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]] was born.<ref>{{Cite web |url=http://collection.sciencemuseum.org.uk/objects/co32957/type-used-for-original-morse-telegraph-1835-movable-type |title=Type used for original morse telegraph, 1835 |website=[[Science Museum, London|Science Museum]] |access-date=2017-12-05 |quote=Samuel Morse was one of the pioneers of electric telegraphy. Prompted by receiving news of his wife's death too late to attend her funeral, Morse was determined to improve the speed of long distance communications (which at that point relied on horse messengers).}}</ref> 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.<ref>{{cite web |url=https://distantwriting.co.uk/cookewheatstone.html |title=3. Cooke and Wheatstone |last=Roberts |first=Steven |website=Distant Writing: A History of the Telegraph Companies in Britain between 1838 and 1868}}</ref> In 1841 [[Alexander Bain (inventor)|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]]s to closely regulate the speed of the clockwork. It was patented, along with other devices, on April 21, 1841.<ref>{{cite web |url=http://distantwriting.co.uk/bain.html |title=Distant Writing – Bain |author=Steven Roberts}}</ref>

By 1846, the [[Samuel Morse|Morse]] telegraph service was operational between Washington, D.C., and New York. [[Royal Earl House]] 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]]. 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.<ref>{{cite journal |journal=RTTY Journal |volume=25 |issue=9 |date=October 1977 |page=2 |url=https://archive.org/details/VO25NO8/page/n1/mode/2up |title=Silent Key – Edward Kleinschmidt}}</ref>

[[File:Printing Telegraph.jpg|thumb|[[David Edward Hughes|Hughes]] telegraph, an early (1855) teleprinter built by Siemens and Halske. The [[centrifugal governor]] to achieve synchronicity with the other end can be seen.|alt=]]
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.<ref name="Clarkson">{{cite web |url=http://people.clarkson.edu/~ekatz/scientists/hughes.html |title=David Edward Hughes |access-date=September 29, 2010 |date=April 14, 2007 |publisher=Clarkson University |archive-url=https://web.archive.org/web/20080422072443/http://people.clarkson.edu/~ekatz/scientists/hughes.html |archive-date=April 22, 2008}}</ref>

In France, [[Émile Baudot]] 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.<ref>{{cite web |last=Hobbs |first=Alan G. |title=Five-unit codes |url=http://www.nadcomm.com/fiveunit/fiveunits.htm |access-date=May 1, 2012}}</ref>

During 1901, Baudot's code was modified by [[Donald Murray (inventor)|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]], 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.<ref>{{cite magazine |last=Foster |first=Maximilian |date=August 1901 |title=A Successful Printing Telegraph |magazine=[[World's Work|The World's Work: A History of Our Time]] |volume=II |pages=1195–1199 |url=https://books.google.com/books?id=IF6tNZnhO7wC&pg=PA1195 |access-date=July 9, 2009}}</ref> 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 [[letter frequencies|frequently used characters]]. The Murray code also introduced what became known as "format effectors" or "[[control character]]s" – the [[Carriage return|CR]] (Carriage Return) and [[Newline|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.<ref name="query.nytimes.com"/>

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]], 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'.<ref>{{cite patent |country=US |status=Patent |number=888335 |gdate=May 1908}}</ref> In 1904, Krum filed a patent for a 'type wheel printing telegraph machine'<ref>{{cite patent |country=US |status=Patent |number=862402}}</ref> 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.<ref>{{cite patent |country=US |status=Patent |number=1286351 |fdate=May 1910 |gdate=December 1918}}</ref>

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.<ref name="Colin Hempstead, William E. Worthington 2005 605">{{cite book |author=Colin Hempstead, William E. Worthington |url=https://books.google.com/books?id=0wkIlnNjDWcC&pg=PA605 |title=Encyclopedia of 20th Century Technology |year=2005 |page=605 |publisher=Routledge |isbn=9781579584641}}</ref><ref>{{cite web |url=http://www.baudot.net/teletype/MPT.htm |title=Morkum Printing Telegraph Page Printer |access-date=2011-08-15}}</ref>

In 1916, [[Edward Kleinschmidt]] filed a patent application for a typebar page printer.<ref>{{cite patent |inventor-last=KLEINSCHMIDT |inventor-first=E. |title=TELEGRAPH PRINTER |gdate=Apr 14, 1916 |country=US |number=1448750 |status=Patent}}</ref> In 1919, shortly after the [[Morkrum]] 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"<ref>{{cite patent |inventor-last=KLEINSCHMIDT |inventor-first=E. |title=METHOD OF AND APPARATUS FOR OPERATING PRINTING TELEGRAPHS |gdate=May 1, 1919 |number=1463136 |country=US |status=Patent}}</ref> which included an improved start-stop method.<ref name=historytelcom>{{cite book |last=Huurdeman |first=Anton A. |title=The Worldwide History of Telecommunications |publisher=Wiley-IEEE |year=2003 |pages=302 |isbn=0-471-20505-2}}</ref> The basic start-stop procedure, however, is much older than the Kleinschmidt and Morkrum inventions. It was already proposed by D'Arlincourt in 1870.<ref>{{cite book |last1=Deckert |first1=Jürgen |last2=Kösling |first2=Heinz |date=1987 |title=Fernschreibtechnik |trans-title=Teletype Technology |language=de |location=Berlin |publisher=Militärverlag der [[East Germany|Deutschen Demokratischen Republik]] ([[Volkseigener Betrieb|VEB]]) |isbn=3-327-00307-6}}</ref>

[[File:Siemens t37h without cover.jpg|thumb|Siemens t37h (1933) without cover]]
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]] 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.<ref name=historytelcom/>

In 1924 Britain's [[Creed & Company]], founded by [[Frederick G. Creed]], 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.{{Citation needed|date=November 2017}}

A teleprinter system was installed in the [[Bureau of Lighthouses]], Airways Division, Flight Service Station Airway Radio Stations system in 1928, carrying administrative messages, flight information and weather reports.<ref>{{cite web |last=Schamel |first=John |title=Flight Service History 1920-1998 |website=Air Traffic Control History |date=2016-10-19 |url=http://www.atchistory.org/flight-service-history-1920-1998/}}</ref> By 1938, the teleprinter network, handling weather traffic, extended over 20,000 miles, covering all 48 states except Maine, New Hampshire, and South Dakota.<ref>{{Cite web |url=https://www.faa.gov/about/media/b-chron.pdf |title=FAA HISTORICAL CHRONOLOGY, 1926-1996 |website=faa.gov |date=2005-12-17 |archive-url=https://web.archive.org/web/20131105165930/http://www.faa.gov:80/about/media/b-chron.pdf |archive-date=2013-11-05 |url-status=dead}}</ref>

==Ways in which teleprinters were used==
Teleprinters could use a variety of different communication channels. These included a simple pair of wires, [[public switched telephone network]]s, dedicated non-switched telephone circuits (leased lines), [[switched communication network|switched networks]] that operated similarly to the public telephone network ([[telex]]), and radio and [[microwave]] links (telex-on-radio, or TOR). 

There were at least five major types of teleprinter networks:
* Exchange systems such as [[Telex]] and [[Telex#Teletypewriter eXchange|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]] 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 [[Punched tape|paper tape]] and transmit them without pauses for typing.
* [[Leased line]] and [[radioteletype]] networks arranged in point-to-point and / or multipoint configurations supported [[data processing]] 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]], [[Western Union]], [[Plan 55-A]]. 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".<ref>{{Cite web |title=AP teletype machine |url=https://history.capitolbroadcasting.com/media-assets/ap-teletype-machine/ |access-date=2022-03-05 |website=CBC History |language=en-US}}</ref> Examples were operated by [[Associated Press]], [[National Weather Service]], [[Reuters]], and United Press (later [[UPI]]). 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.<ref>{{cite patent |title=Signaling system |status=Patent |country=US |number=2364357 |gdate=29 March 1944}}</ref>

Before the [[computer revolution]] (and [[data processing|information processing]] performance improvements thanks to [[Moore's law]]) made it possible to securely encrypt voice and [[video call]]s, teleprinters were long used in combination with electromechanical or electronic [[cryptographic]] devices to provide secure [[communication channel]]s. Being limited to text only was an acceptable trade-off for security.

==Teleprinter operation==
[[Image:Baudotkeyboard.png|right|thumb|upright=1.85|[[Alphanumeric keyboard|Keyboard]] of a [[Baudot code|Baudot teleprinter]], with 32 keys, counting the space bar (only partially visible in this picture; the key left blank in this layout is not the space bar<ref>cf. page C-8 / Fig. C-3; PDF page 75; "[https://books.google.com/books?id=AuIOu97MduQC Principles of Telegraphy (Teletypewriter)]"</ref>)]]
[[File:International Telegraph Alphabet 2 brightened.jpg|thumb|upright=1.85|[[International Telegraph Alphabet No. 2]] development of the Baudot–Murray code]]

Most teleprinters used the 5-[[bit]] [[International Telegraph Alphabet No. 2]] (ITA2). This was limited to 32 codes (2<sup>5</sup> = 32), which was insufficient to encode all the alphabet as well as numbers and other characters. Therefore, the keyboard used the "FIGS" (for "figures") and "LTRS" (for "letters") keys to allow two encoding [[state (computer science)|state]]s, with a total of 60 codes by sending one of two reserved characters to indicate the state of the following encoded stream (the letters were single case only). Special versions of teleprinters had FIGS characters for specific applications, such as weather symbols for weather reports. The ITA2 code was used [[asynchronous start-stop|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]], were introduced but never became as popular as ITA2.

[[Mark and space|''Mark'' and ''space'']] are terms describing [[logic level]]s in teleprinter circuits. The native mode of communication for a teleprinter is a simple series [[direct current circuit|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]]) [[null character]].

Teleprinter circuits were generally leased from a communications [[common carrier]] and consisted of ordinary [[telephone cable]]s that extended from the teleprinter located at the customer location to the common carrier [[telephone exchange|central office]]. These teleprinter circuits were connected to switching equipment at the central office for [[Telex]] and [[Telegraphy#TWX|TWX]] service. [[Private line]] teleprinter circuits were not directly connected to switching equipment. Instead, these private line circuits were connected to [[network hub]]s and [[repeater]]s 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]].

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]], 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 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.<ref>{{cite web |website=Sam's Telecomms Documents Repository |url=http://www.samhallas.co.uk/repository/telegraph/introduction_to_RTTY.pdf |title=Introduction to RTTY}}<!-- http://www.samhallas.co.uk/repository/telegraphy.htm --></ref> This is true especially on [[high frequency]] 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.<ref>{{Cite web |url=http://w7ay.net/site/Technical/RTTY%20Demodulators/index.html |title=RTTY Demodulators}}</ref> 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]] (22.0 [[millisecond|ms]] per bit), a "66 speed" machine is geared at 50.0 [[baud]] (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]] [[radioteletype|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]] 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.

The teleprinter circuit was often linked to a 5-bit [[punched tape|paper tape]] 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]].

Communication by radio, known as ''[[radioteletype]]'' 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]] 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===
{{Main|Control character}}
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]]), advance to the same column of the next line ([[line feed]]), 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 [[Enquiry character|ENQ]] (control E) signal, if enabled.<ref name="Hereis">{{Cite web |url=http://www.pdp8online.com/asr33/pics/main_back.shtml |title=ASR 33 Teletype Rear View of Main Assembly |website=www.pdp8online.com}}</ref><ref name="AnotherHereis">{{Cite web |url=http://www.k7tty.com/development/teletype/model-32/index.html |title=TELETYPE MODEL 32ASR. |website=www.k7tty.com}}</ref> 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===
[[File:Bundesarchiv Bild 183-2008-0516-500, Fernschreibmaschine mit Telefonanschluss.jpg|thumb|A [[Creed & Company]] Teleprinter No. 7 in 1930]]
British [[Creed & Company]] built teleprinters for the [[General Post Office|GPO]]'s teleprinter service.<ref>{{Citation |title=Baudot.net: Creed & Company, Ltd. |url=http://www.baudot.net/creed.htm}}</ref>
* 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]] in 1947 uses a 14-bit [[start-stop transmission]] 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]], 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.<ref>{{cite web |title=Gretag ETK-47 14-bit teleprinter system |website=Crypto Museum |date=2016-07-04 |url=https://www.cryptomuseum.com/telex/gretag/etk47/}}</ref><ref>{{cite web |url=http://www.jproc.ca/crypto/etk_series.html |title=ETK teletype equipment series}}</ref><ref>{{cite web |author=F. Dörenberg |url=https://www.nonstopsystems.com/radio/hellschreiber-modes-other-mfrs-non-UK.htm#ETK |title=Other manufacturers of teleprinter machines that use the Hellschreiber principle |at=Dr. Edgar Gretener AG (Gretag)}}</ref><ref>{{cite web |url=https://www.nsa.gov/Portals/70/documents/news-features/declassified-documents/friedman-documents/patent-equipment/FOLDER_543/41781009082006.pdf |title=The Hagelin - Gretener Cipher Teleprinter}}</ref>

===Kleinschmidt Labs===
In 1931, American inventor Edward Kleinschmidt formed [[Kleinschmidt Inc|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]], which then merged with the [[Marchant Calculator|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]] made their first commercial installation of a printing telegraph with the Postal Telegraph Company in Boston and New York in 1910.<ref>{{cite book |author=Colin Hempstead, William E. Worthington |url=https://books.google.com/books?id=0wkIlnNjDWcC&pg=PA605 |title=Encyclopedia of 20th-century technology |year=2005 |page=605 |publisher=Routledge |isbn=9781579584641}}</ref> It became popular with railroads, and the [[Associated Press]] adopted it in 1914 for their [[wire service]].<ref name="Colin Hempstead, William E. Worthington 2005 605"/><ref>{{cite web |url=http://www.baudot.net/teletype/MPT.htm |title=Morkum Printing Telegraph Page Printer |access-date=August 22, 2011}}</ref> Morkrum merged with their competitor Kleinschmidt Electric Company to become Morkrum-Kleinschmidt Corporation shortly before being renamed the Teletype Corporation.<ref name="Queensland">{{cite web |url=http://www.telemuseum.org/teleprinters.html |title=Queensland Telecommunications Museum – Teleprinters |publisher=Queensland Telecommunications Museum}}</ref><ref>{{cite book |url=https://archive.org/details/morkrumsystemofp00earl |title=The Morkrum System of Printing Telegraphy |author=Earle, Ralph H. |year=1917 |location=Chicago |publisher=Armour Institute of Technology (thesis)}}</ref>

===Olivetti===
[[File:Telescrivente CEP - Calcolatrice Elettronica Pisana.jpg|thumb|Olivetti Teleprinter]]
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===
[[File:Fernscheiber 01.jpg|thumb|right|[[Siemens]] ''Fernschreiber 100'' teleprinter]]
[[Siemens & Halske]], later [[Siemens]], a German company, founded in 1847.
* Teleprinter Model 100 Ser 1 (end of the 1950s)&nbsp;– Used for Telex service<ref name="Queensland"/>
* Teleprinter Model 100 Ser. 11&nbsp;– 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 [[Floppy disk#3.5-inch floppy disk|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===
{{main|Teletype Corporation}}
[[File:ASR-33 at CHM.agr.jpg|thumb|A [[Teletype Model 33]] ASR teleprinter, with [[punched tape]] reader and punch, usable as a [[computer terminal]]]]
The '''Teletype Corporation''', a part of [[AT&T Corporation|American Telephone and Telegraph Company]]'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]] 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.<ref>{{cite web |url=http://www.kekatos.com/teletype/ |archive-url=https://web.archive.org/web/20080603235022/http://www.kekatos.com/teletype/ |title=History of The Teletype Corporation |access-date=March 3, 2010 |archive-date=June 3, 2008 |date=June 24, 2003 |url-status=dead}}</ref> 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.<ref>{{cite web |url=https://tmsearch.uspto.gov/bin/showfield?f=doc&state=4805:5200jd.2.9 |title=US trademark database |website=uspto.gov}}</ref>

Teletype machines tended to be large, heavy, and extremely robust, capable of running non-stop for months at a time if properly lubricated.<ref>{{cite book |url=http://www.bitsavers.org/pdf/teletype/138_Model15_Adj_Oct41.pdf |archive-url=https://web.archive.org/web/20110111174700/http://www.bitsavers.org/pdf/teletype/138_Model15_Adj_Oct41.pdf |archive-date=January 11, 2011 |url-status=dead |title=Adjustments, Type Bar Page Printer, (Model 15) |year=1941 |publisher=Teletype Corporation |location=Chicago}}</ref> 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
* [[Teletype Model 28|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
* [[Teletype Model 33|Model 33]] = same as Model 32 but for 8 level ASCII-plus-parity-bit, 72 char./line, used as computer terminal; optional tape punch and reader.<ref>{{Cite web |url=https://www.pdp8online.com/asr33/asr33.shtml |title=ASR 33 Teletype Information |website=www.pdp8online.com}}</ref>
* 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), upper and lower case, and red/black printing; 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===
{{main|Silent 700}}
[[Texas Instruments]] developed its own line of teletypes in 1971, the [[Silent 700]]. Their name came from the use of a [[Thermal printing|thermal printer]] head to emit copy, making them substantially quieter than contemporary teletypes using [[Printer (computing)#Impact printers|impact printing]], 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]]s and some had internal storage, initially [[cassette tape]] in the 1973 Models 732/733 ASR and later [[bubble memory]] in the 1977 Models 763/765, the first and one of the few commercial products to use the technology.<ref>{{cite web |url=http://oldvcr.blogspot.com/2022/02/refurb-weekend-texas-instruments-silent.html |title=Old Vintage Computing Research: Refurb weekend: Texas Instruments Silent 700 Model 745 teletype |date=February 17, 2022}}</ref> 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==
[[File:Telex machine ASR-32.jpg|thumb|A Teletype Model 32 ASR used for Telex service]]
{{main|Telex|Telegraphy#Telex}}
<!-- Note: Do not drop the sub-item ==Telex== unless you update the links to it. There is at least one item that points to Telex using Teleprinter#Telex as the link. (probably should be redirected to telegraphy--agr) -->
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 "[[Telegraphy#TWX|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 modem|Bell 103]] 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]] to prevent [[Plain old telephone service|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 character code | 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.<ref name="Sloan">{{cite book |title=American Journalism: History, Principles, Practices |editor=W. David Sloan, Lisa Mullikin Parcell |page=[https://archive.org/details/americanjournali0000unse_r6h5/page/365 365] |publisher=McFarland |date=April 10, 2002 |isbn=978-0-7864-1371-3 |url=https://archive.org/details/americanjournali0000unse_r6h5/page/365}}</ref> 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").<ref>{{Cite book |url=https://archive.org/details/LinotypeHandbookForTeletypesetterOperation1951 |title=The Linotype Handbook for Teletypesetter Operation |last=Mergenthaler Linotype Company |date=1951 |publisher=digital reprint by www.CircuitousRoot.com |others=Dr. David M. MacMillan |language=EN}}</ref>

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 "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.<ref>{{cite web |url=https://www.smecc.org/teletypes_in_typesetting.htm |title=Teletypes in Typesetting |author=Doug Kerr |publisher=Southwest Museum of Engineering, Communications and Computation |location=Glendale, Arizona, USA |access-date=2017-04-25}}</ref>

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 columnist|syndicated columns]], [[News agency|news agency news]], [[classified advertising]], 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]] for storage, editing, and eventual feed to a phototypesetting machine.

==Teleprinters in computing==<!-- This section is linked from [[Line printer]] -->
[[File:ASR-33 Teletype terminal IMG 1658.jpg|thumb|A Teletype Model 33 ASR with paper tape reader and punch, as used for early [[modem]]-based computing]]
Computers used teleprinters for input and output from the early days of computing. [[Punched card]] readers and fast printers replaced teleprinters for most purposes, but teleprinters continued to be used as interactive [[time-sharing]] [[computer terminal|terminals]] until video [[computer display|displays]] became widely available in the late 1970s.

Users typed commands after a [[Command-line interface#Command prompt|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]].

[[Punched tape|Paper tape]] 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]] 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 Equipment Corporation|Digital's]] [[RT-11]], serial communication lines were often connected to teleprinters and were given device names starting with {{mono|tt}}. This and similar conventions were adopted by many other operating systems. [[Unix]] and [[Unix-like]] [[operating system]]s use the [[prefix]] {{mono|tty}}, for example {{mono|/dev/tty13}}, or {{mono|pty}} (for pseudo-tty), such as {{mono|/dev/ptya0}}, 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 [[system console|console]] 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]]-to-RS-232 converter attached to a computer's USB port, or even a [[terminal emulator]] application in the window system using a [[pseudoterminal]] 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]], personal computer, [[inkjet printer]], [[email]], and the Internet.

In the 1980s, [[packet radio]] 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 code|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.

==See also==
* [[Letter-quality printer]]
* [[Plan 55-A]], a [[message switching]] system for telegrams
* [[Radioteletype]]
* [[Siemens and Halske T52]] – the ''Geheimfernschreiber'' (''secrets teleprinter'')
* [[Universal asynchronous receiver-transmitter]], which made it easy to connect teleprinters and terminals emulating teleprinters to computers

== References ==

{{Reflist|30em}}

== Further reading ==
* {{Cite magazine |last=Foster |first=Maximilian |title=A Successful Printing Telegraph |magazine=The World's Work |volume=II |issue=5 |pages=1195–1200 |publisher=Doubleday, Page & Co. |location=New York |date=September 1901 |url=https://books.google.com/books?id=IF6tNZnhO7wC&pg=PA1195 |access-date=April 29, 2012}}
* {{cite book |last=Gannon |first=Paul |year=2006 |title=Colossus: Bletchley Park's Greatest Secret |location=London |publisher=Atlantic Books |isbn=978-1843543312}} On the role of the teleprinter code in WWII
* {{cite book |editor1=A. G. Hobbs |editor2=E. W. Yeomanson |editor3=A.C. Gee |title=Teleprinter Handbook |edition=2nd |publisher=[[Radio Society of Great Britain|RSGB]] |isbn=0-900612-59-2 |year=1983}}
* {{cite magazine |url=https://books.google.com/books?id=g_EDAAAAMBAJ&pg=PA577 |title=Teletype Messages Sent Through Switch Board |magazine=[[Popular Mechanics]] |date=April 1932 |quote=AT&T offering two way service through switchboards |page=577 |publisher=Hearst Magazines |issn=0032-4558}}

== External links ==
{{commons}}
* [http://www.kekatos.com/teletype/History_Of_The_Morkrum_Company_1925.htm A first-hand report of Teletype Corporation's early years] {{Webarchive|url=https://web.archive.org/web/20090312005705/http://www.kekatos.com/teletype/History_Of_The_Morkrum_Company_1925.htm |date=March 12, 2009 }}
* [http://www.circuitousroot.com/artifice/telegraphy/tty/gallery/index.html A Gallery of Teletype Images]
* [http://www.rtty.com/history/nelson.htm History of Teletypewriter Development] by R.A. Nelson
* [http://www.baudot.net/docs/haynes--notes.pdf "Some Notes on Teletype Corporation"]
* [https://web.archive.org/web/20111029062458/http://www.mass.gov/?pageID=eohhs2terminal&L=6&L0=Home&L1=Consumer&L2=Disability+Services&L3=Services+by+Type+of+Disability&L4=Deaf%2c+Late-Deafened%2c+and+Hard+of+Hearing&L5=Assistive+Technology+and+Hearing+Ear+Dogs&sid=Eeohhs2&b=terminalcontent&f=mcdhh_c_at_tty&csid=Eeohhs2 Mass.gov: TTY explanation and government best practices for TTY use]

=== Patents ===
* {{cite patent |country=US |status=Patent |number=1665594 |title=Telegraph printer (Type 12 Teletype) |fdate=June 1924 |gdate=April 1928}}
* {{cite patent |country=US |status=Patent |number=1745633 |title=Telegraph receiver (Type 14 Teletype) |fdate=December 1924 |gdate=February 1930}}
* {{cite patent |country=US |status=Patent |number=1904164 |title=Signalling system and apparatus therefor (Type 15 Teletype) |fdate=July 1930 |gdate=April 1933}}
* {{cite patent |country=US |status=Patent |number=3507997 |title=Frequency-Shift Teletypewriter |fdate=August 1966 |gdate=April 1970}}

{{Telecommunications}}
{{Authority control}}

[[Category:History of telecommunications]]
[[Category:Impact printing]]
[[Category:Printing technology]]
[[Category:Telegraphy]]
[[Category:Typewriters]]