Columbia University Computing History   

Teletype Machines

The Teletype machines from the Teletype Corporation, Skokie, Illinois, were ubiquitous at non-IBM computing installations in the 1960s and 70s. Notably, they were often supplied with minicomputers such as the Digital Equipment Corporation PDP-11/20, for example (at the lab where I worked at Mt. Sinai Hospital in NYC in the early 1970s). Left: An ASR33 without built-in telephone. Below: The Teletype Corporation ASR 33 Teletype (1967). 110 bps, 8-level ASCII encoding (uppercase only); 4-row Automatic Send Receive, 101C Dataset (modem); Bell System TWX service. Teletypes were nearly 100% mechanical with no electronics to speak of and required regular maintenance and lubrication.

The ASR33 was by far the most common Teletype model in the mid-to-late 1960s, although we did have an ASR37 in the machine room for some time. But as to the model 33... The paper is roll-fed. The paper tape device was be used for sending recorded keystrokes or other data, or to capture incoming material (thus Automatic Send Receive). The KSR models (Keyboard Send Receive) lacked the paper tape reader/punch. Most non-IBM computers of the 1960s until the mid-1970s — such as DEC PDP-xx minicomputers — came with a Teletype console terminal. The 33 and 35 models were uppercase only; the 37 model had upper and lower case. To this day certain characteristics of the Teletype live on in the 110-"baud" 2-stop-bits configuration required to synchronize with the Teletype printing mechanism, still supported by most modems, serial ports, and software.

Pushing the keys was good exercise; the keys traveled a good half inch before making contact, and resistance was considerable. The Answerback reply was programmed by breaking teeth off a plastic gear. Teletypes in one form or another go back to about 1907. They were used originally as automatic Telegraph and Telegram machines. Teletypes reached their familiar mature form in the 1920s and the ASR33 was announced 1962.

In addition to sending and receiving text, Teletypes could also be used to transcribe text from keyboard to paper tape for storage and eventual re-use, and also to create line-printer carriage-control tape loops for printers such as the IBM 1403. In this case heavy-duty Mylar tape was often used instead of paper tape. At Columbia during the mainframe era, users could have operators "mount" custom printer control tapes for their jobs (see a story about this here).

Gallery

• Teleprinter, Wikipedia, accessed 25 March 2021.
• Teletype Model 33, Wikipedia, accessed 25 March 2021.
• Teletype Model 37, Wikipedia, accessed 25 March 2021.
• Carriage Control Tape, Wikipedia, accessed 25 March 2021.
• History of Teletypewriter Development, monograph, R.A. Nelson (K. M. Lovitt, Editor), Teletype Corporation, October 1963.
• A Synopsis of Teletype Corporation History, Don Robert House, 2001.
• The North American Data Communications Museum (NADCOMM)
• The Teletype Story (50th anniversary of the Teletype, 1957, commemoration booklet)
• Teletype Corp (photos and specs of many models).
• Morkum Model GPE Perferator ("Iron Horse")
• Nurturing the Network: Women and the Communications Industry (IEEE), includes a 1946 film clip of Teletype operation.
• Teletypesetter Gallery of Images, circuitousroot.com, accessed 25 March 2021 (PDP-8 with Teletype).
• An amusing Photo, Bell Labs, 1972: Ken Thompson and Dennis Ritchie, PDP-11/20, two ASR33s.
• Birth of an Internet Lo and Behold, Bradley Thornton, linboard.org, accessed 25 March 2021 (ttyasr33b.jpg)
• Teletype ASR 33, Computermuseum der Stuttgarter Informatik, uni-stuttgart.de, accessed 25 March 2021.
• FAQ - Using a Teletype to Interface with a Computer, vintagecomputer.net, accessed 25 March 2021 (print ad).
• The Digital Equipment Corporation PDP-7, soemtron.org, accessed 25 March 2021 (pdp7).
• Benj Edwards, A brief history of computer displays, PC World, accessed 25 March 2021 (pdp7).
• PDP-12 Laboratory Instrument Computer User Handbook, Digital Equipment Corporation (1969), converted to HTML by Carl R. Friend, accessed 25 March 2021 (pdp7).

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