Model 33 Teletype

Model 33 Teletype. The Model 33 Teletype was a electromechanical teleprinter manufactured by the Teletype Corporation, a subsidiary of AT&T, and introduced in 1963. It became one of the most influential data terminals of the 20th century by being the first major device to utilize the then-new ASCII character encoding standard. Its rugged design, relatively low cost, and compatibility with emerging minicomputer systems like those from Digital Equipment Corporation and Data General made it a ubiquitous fixture in computing, telecommunications, and news media for nearly two decades.

History and development

The Model 33 was developed by engineers at the Teletype Corporation, which had a long history of supplying teleprinters to the Bell System and the United States Department of Defense. It was designed as a successor to the earlier Model 32 Teletype, with the primary innovation being its native support for the ASCII code, which was standardized in 1963 by the American Standards Association. The development was influenced by the needs of the SAGE air defense system and a growing demand from the nascent computer industry for a standardized, reliable input/output device. Production began at Teletype's main plant in Skokie, Illinois, and the unit quickly found a market beyond traditional Western Union telegraphy into university computer centers and corporate data processing departments.

Technical specifications

The Model 33 was an entirely electromechanical machine with a keyboard, printer, and optional punched tape reader and punch. It operated at a standard speed of 10 characters per second, utilizing a rotating type cylinder and hammer mechanism for printing on fanfold paper. Its keyboard followed a 4-row, shift key layout that directly corresponded to the 7-bit ASCII code set, producing 128 possible characters. Data was transmitted serially via a standard 20 mA current loop interface, and later models offered optional RS-232 electronic interfaces for connection to modems and computers. The machine was famously noisy during operation due to its solenoids, clutches, and printing mechanism, a characteristic sound in many early computer rooms.

Operation and usage

In operation, the Model 33 functioned both as a stand-alone teleprinter for sending messages over leased lines and as a direct computer terminal. In the latter role, it was commonly connected to PDP-8, PDP-11, and Nova minicomputers, serving as the primary user interface for time-sharing systems, program entry, and debugging. The optional ASR-33 (Automatic Send-Receive) model, with its integrated paper tape reader and punch, was particularly vital for storing and loading programs and data. These machines were central to the development of early ARPANET protocols and were used by pioneers at institutions like MIT, Stanford University, and the University of California, Berkeley. They were also widely employed in newsrooms by organizations such as the Associated Press for wire service copy.

Variants and models

The primary variants were defined by their tape capabilities. The KSR-33 (Keyboard Send-Receive) was a basic model with only a keyboard and printer. The ASR-33 included both a reader and punch for eight-level punched tape, making it the most common and versatile version for computing. A receive-only model, the RO-33, was also produced for dedicated printing applications. Later in its production run, some units were offered with a 30 character-per-second printing mechanism. While the basic design remained consistent, incremental improvements were made to components like the tape reader and power supply throughout its manufacturing life, which ended in 1981.

Impact and legacy

The impact of the Model 33 on computing and communications was profound. It established ASCII as the dominant character code for the industry, a standard that remains in use today. Its affordability and availability accelerated the adoption of interactive computing in the 1960s and 1970s, influencing the culture of early programming and hacker communities at places like the MIT Artificial Intelligence Laboratory. The Model 33 was directly responsible for the persistence of the QWERTY-based keyboard layout in computing and the convention of the newline character sequence. It was largely supplanted by quieter, faster, and more capable video display terminals like the VT100 from Digital Equipment Corporation and the IBM 3270, but its legacy is evident in modern terminal emulators and the foundational protocols of the Internet.

Category:Teleprinters Category:Computer terminals Category:American inventions Category:AT&T