Teletype Model 33
The Teletype Corporation introduced the Model 33 as a commercial product in 1963,[1] after it had originally been designed for the United States Navy.
[5] Because of its low price and ASCII compatibility, the Model 33 was widely used with early minicomputers, and the large quantity of the teleprinter sold strongly influenced several de facto standards that developed during the 1960s and 1970s.
[7] Another 100,000 were made in the next 18 months, and Serial Number 600,000, manufactured in the United States Bicentennial year 1976, was painted red-white-and-blue, and shown around the country.
[8] The Model 33 originally cost about $1000[3] (equivalent to $10,000 today), much less than other teleprinters and computer terminals in the mid-1960s, such as the Friden Flexowriter and the IBM 1050.
The machines had good durability and faced little competition in their price class, until the appearance of Digital Equipment Corporation's DECwriter series of teleprinters.
The trigram "tty" became widely used as an informal abbreviation for "Teletype", often used to designate the main text input and output device on many early computer systems.
[15] More-advanced video terminals, such as the Digital Equipment Corporation VT52 (1975), the ADM-3A (1976), and the VT100 (1978), could communicate much faster than electromechanical printers, and could support use of a full-screen text editor program without generating large amounts of paper printouts.
[16] Teletype machines were gradually replaced in new installations by much faster dot-matrix printers and video terminals in the middle-to-late 1970s.
The interface between the paper tape reader and the rest of the terminal is completely mechanical, with power, clock, and eight data bits (which Teletype called "intelligence") all transmitted in parallel through metal levers.
Sensing of punched holes by the paper tape reader is done by using metal pins which mechanically probe for their presence or absence.
[27][28] The Teletype Model 33 contains an answer-back mechanism that is generally used in dial-up networks such as the Teletypewriter Exchange Service (TWX).
The sole electric motor in the machine has to be left running continuously whenever unattended operation is expected, and is designed to withstand many hours of idling.
The communications module in the Model 33 is known as a Call Control Unit (CCU), and occupies the space to the right of the keyboard and printer.
The Model 32 line used the same mechanism and looked identical, except for having a three-row keyboard and, on the ASR version, a five-hole paper tape reader and punch, both appropriate for Baudot code.
[30] The tape reader is mounted separately from the printer-punch mechanism on the left side of the console, and behind it is a tray for storing a manual, sheets of paper, or other miscellanea.
All versions of the Model 35 have a copy holder on the printer cover, making it more convenient for the operator when transcribing written material.
The Model 35 was widely used as terminals for the minicomputers and IMPs to send and receive text messages over the very early ARPANET, which later evolved into the Internet.
A two-color inked ribbon and additional ASCII control codes allowed automatic switching between red and black output while printing.
A wider pin-feed platen and typing mechanism allowed printing 132 columns on fan-fold paper, making its output similar to the 132-column page size of the then industry-standard IBM 1403 model printers.
