Computer terminal

A computer terminal is an electronic or electromechanical hardware device used for entering data into, and displaying data from, a computer or a computing system.

Historical

Early user terminals connected to computers were generally electromechanical teleprinters (TTYs), such as the model 33 Teletype. However these were too slow for most production uses. By the early 1970s, many in the computer industry realized that an affordable video data entry terminal could supplant the then ubiquitous punch 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.

Related Topics:
Teleprinter - Model 33 Teletype - 1970s - Punch card - Minicomputer - Integrated circuit - Storage tube - Tektronix

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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 line, often using the RS-232 serial interface. IBM systems communicated over a coaxial cable using IBM's SNA protocol.

Related Topics:
Logic gates - CPU - Microprocessor - Mainframe computer - RS-232 - IBM - Coaxial cable - SNA

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Later, so called intelligent terminals were introduced, such as the VT52 and VT100, both 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. Notable non-VT100 computer terminal types include the IBM 3270, Wyse and Tektronix 4014, but during the late 1970's there were dozens of manufacturers of terminals, many of which had incompatible command sequences.

Related Topics:
VT52 - VT100 - Escape sequences - Cursor - IBM 3270 - Wyse - Tektronix 4014 - 1970

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While early IBM PCs had single color green screens, these would not have been considered terminals. Note that the screen of a PC did not contain any character generation hardware; all video signals and video formatting was generated by the video display card in the PC. With suitable terminal 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.

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