Tty (Unix) - Historical

Historical

Early user terminals connected to computers were electromechanical teleprinters or teletypewriters (TeleTYpewriter, TTY), such as the Teletype Model 33 ASR, originally used for telegraphy or the Friden Flexowriter. Later printing terminals such as the DECwriter were developed. However printing terminals were limited by the speed at which paper could be printed, and for interactive use the paper record was unnecessary.

By the early 1970s, many in the computer industry realized that an affordable video data entry terminal could supplant the ubiquitous punched cards and permit new uses for computers that would be more interactive. The problem was that the amount of memory needed to store the information on a page of text was comparable to the memory in low end minicomputers then in use. Displaying the information at video speeds was also a challenge and the necessary control logic took up a rack worth of pre-integrated circuit electronics. One company announced plans to build a video terminal for $15,000 and attracted a large backlog of orders, but folded when their engineering plans, which included fabricating their own ICs, proved too ambitious. Another approach involved the use of the storage tube, a specialized CRT developed by Tektronix that retained information written on it without the need to refresh.

The Datapoint 3300 from Computer Terminal Corporation was announced in 1967 and shipped in 1969, making it one of the earliest stand-alone display-based terminals. It solved the memory space issue mentioned above by using a digital shift-register design, and using only 72 columns rather than the later more common choice of 80.

Early video computer displays were sometimes nicknamed "Glass TTYs" and used individual logic gates, with no CPU. One of the motivations for development of the microprocessor was to simplify and reduce the electronics required in a terminal. Most terminals were connected to mainframe computers and often had a green or amber screen. Typically terminals communicate with the computer via a serial port, often using the RS-232 serial interface. IBM systems communicated over a coaxial cable using IBM's SNA protocol. In fact, the instruction design for the Intel 8008 was originally conceived at Computer Terminal Corporation as the processor for the Datapoint 2200.

Later, so-called "intelligent" terminals were introduced, such as the IBM 3270, and the VT52 and VT100 made by DEC, all of which are still widely emulated in software. These were called "intelligent" because they had the capability of interpreting escape sequences to position the cursor and control the display. Some other notable computer terminal types are the various Wyse models (whose Wyse 60 was a best-seller—many are still in use), and the Tektronix 4014.

During the late 1970s and early 1980s, there were dozens of manufacturers of terminals including DEC, Wyse, Televideo, Hewlett Packard, IBM, Lear-Siegler and Heath, many of which had incompatible command sequences.

While early IBM PCs had single color green screens, these screens were not terminals. The screen of a PC did not contain any character generation hardware; all video signals and video formatting were generated by the video display card in the PC. With suitable software PCs could, however, emulate a terminal, if connected to a mainframe computer. Eventually microprocessor-based personal computers greatly reduced the market demand for terminals. Today, most PC telnet clients provide emulation of the most common terminal—the DEC VT100, using the ANSI escape code standard X3.64.