The Teletype Model 33 is an electromechanical teleprinter designed for light-duty office It is less rugged and less expensive than earlier Teletype machines. The Teletype Corporation introduced the Model 33 as a commercial product in 1963^[1] after being originally designed for the US Navy.^[2] There are three versions of the Model 33:

• the Model 33 ASR, (Automatic Send and Receive), which has a built in 8-level paper tape reader and tape punch;
• the Model 33 KSR (Keyboard Send and Receive), which lacks the paper tape reader and punch;
• the Model 33 RO (Receive Only) which has neither a keyboard nor a reader/punch.

The Model 33 was one of the first products to employ the then new ASCII code. A companion Model 32 used the more established five-level Baudot code. Because of its low price and ASCII-compatibility, the Model 33 was widely used with early minicomputers.

History[link]

Teletype Corporation's Model 33 terminal, introduced in 1963, is one of the most popular terminal in the data-communications industry. Over a half-million Model 32's and 33's were made by 1975, and the 500,000th was plated with gold and placed on special exhibit^[3]. Another 100,000 were made in the next 18 months, so that No. 600,000 was painted red-white-and-blue and shown around the country during the last part of, and the year after, the Bi-Centennial year.^[4]

A Model 33 ASR in use in 1978

A Model 33 cost about $700, much less than other teleprinters and computer terminals at the time, such as the Frieden Flexowriter and the IBM 1050. Early video terminals such as the Tektronix 4010 did not become available until 1970 and cost around $10 000. However the introduction of integrated circuits and semiconductor memory later that decade allowed the price of CRT-based terminals to fall below the price of a Teletype. Teletype machines were gradually replaced in new installations by dot-matrix printers and CRT-based terminals in the mid to late 1970s. Basic CRT-based terminals which could only print lines and scroll them are often called glass teletypes to distinguish them from more sophisticated devices.

Teletype Corporation discontinued Model 33 production in 1981.^[5]

Model 33 ASR vs. ASR-33[link]

While the manufacturer called the Model 33 teleprinter with a tape punch and tape reader a Model 33 ASR, many users, specifically computer users, called this equipment an ASR-33. The earliest known source for this Teletype Corporation equipment naming discrepancy comes from Digital Equipment Corporation documentation^[6] where the September 1963 PDP-4 Brochure calls the Teletype Model 28 KSR a "KSR-28" in the paragraph titled "Printer-Keyboard and Control Type 65". This naming discrepancy continued from the Teletype Model 28 to other Teletype equipment in later DEC documentation. For example, Digital Equipment Corporation's PDP-15 Price List from April 1970 lists a number of Teletype Corporation teletypewriters using this alternate naming convention.^[7]

This alternate naming convention was continued as other computer manufacturers published their documentation. For example, Micro Instrumentation and Telemetry Systems sold the Teletype Model 33 ASR as "Teletype ASR-33".

Technical information[link]

The design objective for the Model 33 was a machine that would fit into a small office space, match with other office equipment of the time and operate up to two hours per day on average. Since this machine was designed for light duty use, adjustments that Teletype made in previous teleprinters by turning screws were made by bending metal bars and levers. Many Model 33 parts were not heat treated and hardened. However, the base was die cast but self-tapping screws were used along with parts that snapped together without bolting. In another cost saving measure, the paper tape equipment was dependent on the keyboard and page printer mechanisms. Earlier Teletype machine designs, such as the Model 28 ASR, allowed the user to operate the keyboard to punch tape while transmitting a previously punched tape and to punch a tape while printing something else. Independent use of the paper tape punch and reader is not possible with the Model 33 ASR.^[8]

The Model 33 used the seven-bit upper-case only ASCII code, also known as CCITT International Telegraphic Alphabet No. 5, with one (even) parity bit and 2 stop bits. The Model 33 is usually geared to run at maximum speed ten characters per minute speed, i.e. 100 words per minute (wpm), but other speeds are available: 60 wpm, 66 wpm, 68.2 wpm, and 75 wpm^[9] There were also many typewheel options. The Teletype Parts Bulletin^[10] lists sixty-nine available Model 33 typewheel options.

The Teletype Model 33 contained an answer-back mechanism that was generally used in dial-up networks such as the TWX network. At the beginning of the message, the sending machine could transmit an enquiry character or WRU (Who aRe yoU) code, and the recipient machine would automatically initiate a response which was encoded in a rotating drum that could be programmed by breaking off tabs.^[11] The answer-back drum in the recipient machine would rotate and send an unambiguous identifying code to the sender, so the sender could verify connection to the correct recipient. The WRU code could also be sent at the end of the message. A correct response would confirm that the connection had remained unbroken during the message transmission. Finally the sending machine operator would press the disconnect button. Note that the receiving machine did not need operator intervention. Since messages were often sent across multiple time zones to their destination, it was common to send a message to a location where the receiving machine was operating in an office that was closed and unmanned.

The Teletype Model 33, including the stand, is 34 inches high, 22 inches wide and 18.5 inches deep not including the paper holder. The Teletype Model 33 weighs 75 pounds on the stand, including paper. This machine requires less than 4 amps at 115VAC 60Hz. The recommended operating environment is a temperature of 40 to 110 Fahrenheit, a relative humidity of 2 to 95 percent and an altitude of 0 to 10,000 feet. The printing paper is a 8.44 inch by 4.5 inch diameter roll and the paper tape is a one inch by 1000 foot roll. Ribbons are 0.5 inch wide by 60 yards long with plastic spools and eyelets for proper ribbon reverse operation.

• 

  Model 33 ASR with cover removed

• 

  Rear of unit, with bell and answer back drum to left of motor

• 

  Fully disssembled

Interface[link]

The Model 33 could accommodate an internal modem with an optional acoustic coupler to the right of the keyboard. This was replaced by a blank panel on units operating on a current loop. There were different kinds of Model 33 Call Control Units (CCUs) that included Rotary Dial, Touch-Tone, Card Dialing and Computer Control Private Line variations. In the 1960s and early 1970s minicomputers typically had a 20mA current loop interface for connection to a Teletype machine used as a console terminal and paper tape program loader. As the price of electronic terminals dropped in the late 1970s, the current loop was gradually replaced by an RS-232 interface.

Related machines[link]

A Model 32 used for Telex service. Note the three row keyboard and narrower, 5-level paper tape.

The Model 32 line used the same mechanism and looked identical except for having a three row keyboard and, on the ASR model, a 5 level paper tape reader and punch, both appropriate for Baudot code.

Teletype also introduced a more expensive ASCII Model 35 for heavy duty use. It featured a color scheme that matched the Model 33, but was based on the rugged Model 28 mechanism.

More expensive Teletype systems used photo readers that used light sensors to detect the presence or absence of punched holes in the tape. These could work at much higher speeds (hundreds of characters per second). More sophisticated punches were also available that could run at somewhat higher speeds; Teletype's DRPE punch could operate at speeds up to 240 characters per second.

Historical impact[link]

• ASCII was first used commercially during 1963 as a seven-bit teleprinter code for American Telephone & Telegraph's Teletypewriter eXchange TWX network using Teletype Model 33 teleprinters.
• The Teletype Model 33 series was influential in the development and interpretation of ASCII code characters. In particular, the Teletype Model 33 machine assignments for codes 17 (Control-Q, DC1, also known as XON) and 19 (Control-S, DC3, also known as XOFF) became de facto standards.^[12]
• The programming language BASIC was designed to be written and edited on a low speed Teletype Model 33. The slow speed of the Teletype Model 33 influenced the user interface of minicomputer operating systems, including UNIX.
• A Teletype Model 33 provided Bill Gates' first computing experience.^[13]
• In 1971 Ray Tomlinson chose the @ symbol on his Teletype Model 33 ASR keyboard for use in network email.^[14]
• An Teletype Model 33 ASR had a cameo appearance in the 1994 Coen brothers comedy film, the Hudsucker Proxy Although the film was set in 1958, this teleprinter was not commercially available until 1963.
• The television program Wall Street Week featured a distinctive theme composed by Donald Swartz entitled "TWX in 12 Bars", which featured percussion supplied by a Teletype Model 33 machine.^[15]

References[link]

1. ^ "Auerbach Guide to Alphanumeric Display Terminals", Auerbach Publishers, 1975
2. ^ "A Synopsis of Teletype Corporation History". http://www.baudot.net/docs/house--teletype-corp-synopsis.pdf. 
3. ^ Telephone Engineer & Management, Volume 79, Harcourt Brace Jovanovich Publications, 1975
4. ^ "History of Telegraphy from the Teletype Museum". http://www.baudot.net/docs/slayton--tty-museum.pdf. Retrieved 2012-03-18. 
5. ^ Byte 5: 214. May 1980. 
6. ^ "F-41D PDP-4 Brochure September 1963". p. 5. http://www.bitsavers.org/pdf/dec/pdp4/F-41D_PDP4brochure_Sep63.pdf. 
7. ^ "Digital Equipment Corporation pdp15 Price List". p. 2. http://www.bitsavers.org/pdf/dec/pdp15/1970_PDP15PriceList.pdf. 
8. ^ Jim Haynes. "Some Notes on Teletype Corporation". http://www.baudot.net/docs/haynes--notes.pdf. 
9. ^ Teletype Parts Bulletin 1184B page 35 figure 38
10. ^ Teletype Parts Bulletin 1184B pages 27 - 29 figure 29 - 31
11. ^ "Teletype Rear View of Main Assembly". http://www.pdp8.net/asr33/pics/main_back.shtml. 
12. ^ Tomasi, Wayne. "Electronic Communications Systems: fundamentals through advanced", Prentice Hall, 2001, p. 531.
13. ^ (Manes 1994, p. 27)
14. ^ The @-symbol, part 1 of 2, Shady Characters, July 2011
15. ^ "TWX in 12 Bars". http://www.youtube.com/watch?v=LHc4Ge_HZLc&fmt=18. 

External links[link]

• Photo of a Model 33 ASR
• Keyboard layout for Windows that simulates the ASR33 keyboard
• ASR 33 Teletype Information with movies and sound

Wikimedia Commons has media related to: ASR-33

Look up model in Wiktionary, the free dictionary.

Model may refer to:

Physical[link]

• Physical model, a physical representation of an object
• Scale model, a replica or prototype of an object
• 3D modelling, a 3D polygonal representation of an object, usually displayed with a computer
• Model aircraft
• Car model
• Model building, a hobby centred around construction of material replicas
• Solid modelling, study of unambiguous representations of the solid parts of an object, also called in vitro models
• Model organism, a simple organism used as model in biology
• Model (product), an identifier of a product given by its manufacturer (also called model number).

Human models[link]

• Model (art), a person who poses to be depicted in art, for example in art school
• Model (person), a person employed to display his or her looks or something such as a commercial product
• Fetish model, a model who wears the clothing and/or devices of sexual fetishes
• Promotional model, a person who interacts with consumers to draw attention to and often inform them about a product
• Pseudo-model, (lang mo(u)) a term coined in Hong Kong for young would-be models
• Role model, a person who serves as a behavioural or moral example to others

Nonphysical[link]

Abstract[link]

• Conceptual model, a nonphysical model
• Interpretation (logic), a model is (part of) an interpretation of facts in logic, a mapping of truth values to sentences.
• Mathematical model, an abstract model that uses mathematical language
• Structure (mathematical logic), in model theory often called just a model or semantic model

Applied[link]

• Business model, a framework of the business logic of a firm
• Causal model, an abstract model that uses cause and effect logic
• Computer model, a computer program which attempts to simulate an abstract model of a particular system
• Molecular model, a physicochemical or mathematical description that models the behaviour of molecules
• Data model, a description of database structure
• Economic model, a theoretical construct representing economic processes
• Ecosystem model, a representation of components and flows through an ecosystem
• Graphical model, a probabilistic model for which a graph denotes the conditional independence structure between random variables
• Internal model, a neural process that simulates the response of the motor system in order to estimate the outcome of a motor command
• Macroeconomic model, an economic model representing a national or regional economy
• Mental model, a person's cognitive representation of an idea or thought process
• Modelling (psychology), learning by imitating or observing a person's behavior
• Model-view-controller, an architectural pattern in software engineering
• Pre-clinical development model of a biological process, used in biological or medical research
• Standard Model, the theory in particle physics which describes certain fundamental forces and particles
• Statistical model, in applied statistics, a parameterized set of probability distributions
• Mechanistic model, a description of a system in terms of its constituent parts and mechanisms
• System model (disambiguation), any of several conceptual models that describes and represents a system
• Toy model, a simplified system that illustrates or exhibits the same behaviour as the more complex, general system

Related studies[link]

• Business process modelling, the activity of representing processes of an enterprise
• Enterprise modelling
• Geologic modelling, the applied science of creating computerized models of geologic features
• NLP Modelling, a method in neuro-linguistic programming for acquiring expertise through imitation
• Model theory, study of the representation of mathematical concepts
• Morphological analysis (problem-solving), or morphological modelling, a problem-solving technique used for problems with which causal modelling does not function well
• Process modelling, a core concept in process engineering
• Scientific modelling, the process of generating abstract models for the iterative development of hypotheses as part of the scientific method
• Similitude (model), in engineering, used in the scientific testing of physical models
• Value-added modelling, a technique for measuring teacher performance based on the changes in student scores from year to year on standardized tests

Titles and names[link]

People[link]

• Rick Martel, professional wrestler known as "The Model"
• Walther Model (1891–1945), German Field Marshal of World War II
• Eddie Taubensee, baseball player who was known as "The Model" during his playing days

Groups[link]

• Models (band), an alternative rock group from Australia
• Model (band), a teenage rock group from Turkey
• Movement for Democracy in Liberia, MODEL
• The Models, an English punk band

Artistic works[link]

• "Model," a song by Avail from their 1994 album Dixie (album)
• Models, a 1999 film by Ulrich Seidl
• "Das Model" (spelling on album: "Das Modell"; English version title: "The Model"), a song by the German band Kraftwerk. Later covered by German band Rammstein
• The Model, novel by Norwegian writer Lars Saabye Christensen
• Model (manhwa), a manhwa series by Lee So Young

Geography[link]

• Model, Colorado, an unincorporated town in the United States
• Model, Masovian Voivodeship, east-central Poland

Places[link]

• The Model (Sligo), an arts centre in Sligo, Republic of Ireland

Products[link]

• Working Model, engineering software

See also[link]

• All pages beginning with "Model"
• All pages with titles containing "Model"
• Modell (disambiguation)
• Mode (disambiguation)

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