Computer terminal: Difference between revisions

Revision as of 13:56, 26 January 2025

Revision as of 02:18, 6 July 2025

(11 intermediate revisions by 7 users not shown)

Line 6:

[[File:IBM_2741_(I197205).png|thumb|right|[[IBM 2741]], a widely emulated computer terminal in the 1960s and 1970s<br>(keyboard/printer)]]

A '''computer terminal''' is an electronic or [[electromechanical]] [[computer hardware|hardware]] device that can be used for entering data into, and transcribing<ref>E.g., displaying, printing, punching.</ref> data from, a [[computer]] or a [[computing]] system.<ref>similar to a paraphrase of an [[Oxford English Dictionary]] definition. {{cite web |url=https://english.stackexchange.com/questions/131511/what-is-the-etymology-of-computer-terminal |title=What is the etymology of "[computer] terminal"?}} Based on OED, B.2.d. (terminal), the paraphrase says that a terminal is a device for feeding data into a computer or receiving its output, especially one that can be used by a person for two-way communication with a computer.</ref> Most early computers only had a [[front panel]] to input or display bits and had to be connected to a terminal to print or input text through a keyboard. [[Teleprinter]]s were used as early-day hard-copy terminals<ref name=":0">{{cite web |url=http://www.samhallas.co.uk/repository/telegraph/teletype_story.pdf |title=The Teletype Story}}</ref><ref name="flexowriter-whirlwind">{{cite web|url=https://www.computerhistory.org/timeline/1956/|title=Direct keyboard input to computers|access-date=2024-01-11|archive-date=2017-07-17|archive-url=https://web.archive.org/web/20170717231119/http://www.computerhistory.org/timeline/1956/#169ebbe2ad45559efbc6eb35720ba5f3|url-status=live}}</ref> and predated the use of a computer<ref name=":0" /> screen by decades. The computer would typically transmit a line of data which would be printed on paper, and accept a line of data from a keyboard over a [[Serial communication|serial]] or other interface. Starting in the mid-1970s with [[microcomputers]] such as the [[Sphere 1]], [[Sol-20]], and [[Apple I]], display circuitry and keyboards began to be integrated into [[personal computer|personal]] and [[workstation]] computer systems, with the computer handling character generation and outputting to a [[Cathode-ray_tube|CRT display]] such as a [[computer monitor]] or, sometimes, a consumer TV, but most larger computers continued to require terminals.

Early terminals were inexpensive devices but very slow compared to [[punched card]]s or [[punched tape|paper tape]] for input; with the advent of [[time-sharing]] systems, terminals slowly pushed these older forms of interaction from the industry. Related developments were the improvement of terminal technology and the introduction of inexpensive [[video display]]s. Early Teletypes only printed out with a communications speed of only 75 baud or 10 5-bit characters per second, and by the 1970s speeds of video terminals had improved to 2400 or 9600 {{units|2400|u=bps}}. Similarly, the speed of remote batch terminals had improved to {{units|4800|u=bps}} at the beginning of the decade and {{units|19.6|u=kbps}} by the end of the decade, with higher speeds possible on more expensive terminals.

Line 41:

The DECwriter was the last major printing-terminal product. It faded away after 1980 under pressure from video display units (VDUs), with the last revision (the DECwriter IV of 1982) abandoning the classic teletypewriter form for one more resembling a desktop printer.

Printing terminals required that the print mechanism be away from the paper after a pause in the print flow, to allow an interactively typing user to see what they had just typed and make corrections, or to read a prompt string. As a dot-matrix printer, the DECwriter family would move the print head sideways after each pause, returning to the last print position when the next character came from the remote computer (or local echo).

===Video display unit{{anchor|Video display unit|VDU|VDUs|Video display units (VDUs)}}===

A '''video display unit''' (VDU) displays information on a screen rather than printing text to paper and typically uses a [[cathode-ray tube]] (CRT). VDUs in the 1950s were typically designed for displaying graphical data rather than text and were used in, e.g., experimental computers at institutions likesuch as [[MIT]]; computers used in academia, government and business, sold under brand names likesuch as [[Digital Equipment Corporation|DEC]], [[Engineering Research Associates|ERA]], [[IBM]] and [[UNIVAC]]; military computers supporting specific defence applications such as [[Ballistic Missile Early Warning System|ballistic missile warning systems]] and radar/air defence coordination systems likesuch as [[Back-Up Interceptor Control|BUIC]] and [[Semi-Automatic Ground Environment|SAGE]].

[[File:IBM 2260.jpg|thumb|180px|[[IBM 2260]]]]

Line 199 ⟶ 201:

|journal=[[IEEE Transactions on Computers]] |s2cid=27102280 |date=1971 |volume=C-20 |issue=8 |pages=878–881 |doi=10.1109/T-C.1971.223364 |quote=Terminal cost is currently about $10,000}}</ref>

Most terminals today{{when|date=June 2022}} are graphical; that is, they can show images on the screen. The modern term for graphical terminal is "[[thin client]]".{{Citation needed|date=June 2019}} A thin client typically uses a protocol likesuch as X11 for Unix terminals, or [[Remote Desktop Protocol|RDP]] for Microsoft Windows. The bandwidth needed depends on the protocol used, the resolution, and the [[color depth]].

Modern graphic terminals allow display of images in color, and of text in varying sizes, colors, and [[font]]s (type faces).{{clarify|date=June 2022}}

Line 215 ⟶ 217:

Some dumb terminals had been able to respond to a few escape sequences without needing microprocessors: they used multiple [[printed circuit board]]s with many [[integrated circuit]]s; the single factor that classed a terminal as "intelligent" was its ability to ''process'' user-input within the terminal—not interrupting the main computer at each keystroke—and send a block of data at a time (for example: when the user has finished a whole field or form). Most terminals in the early 1980s, such as ADM-3A, TVI912, Data General D2, DEC [[VT52]], despite the introduction of ANSI terminals in 1978, were essentially "dumb" terminals, although some of them (such as the later ADM and TVI models) did have a primitive block-send capability. Common early uses of local processing power included features that had little to do with off-loading data processing from the [[host (network)|host computer]] but added useful features such as printing to a local printer, buffered serial data transmission and serial handshaking (to accommodate higher serial transfer speeds), and more sophisticated character attributes for the display, as well as the ability to switch emulation modes to mimic competitor's models, that became increasingly important selling features during the 1980s especially, when buyers could mix and match different suppliers' equipment to a greater extent than before.

The advance in microprocessors and lower memory costs made it possible for the terminal to handle editing operations such as inserting characters within a field that may have previously required a full screen-full of characters to be re-sent from the computer, possibly over a slow modem line. Around the mid-1980s most intelligent terminals, costing less than most dumb terminals would have a few years earlier, could provide enough user-friendly local editing of data and send the completed form to the main computer. Providing even more processing possibilities, workstations likesuch as the TeleVideo TS-800 could run [[CP/M-86]], blurring the distinction between terminal and Personal Computer.

Another of the motivations for development of the [[microprocessor]] was to simplify and reduce the electronics required in a terminal. That also made it practicable to load several "personalities" into a single terminal, so a Qume QVT-102 could emulate many popular terminals of the day, and so be sold into organizations that did not wish to make any software changes. Frequently emulated terminal types included:

Line 237 ⟶ 239:

In and around the 1990s, ''thin client'' and [[X terminal]] technology combined the relatively economical local processing power with central, shared computer facilities to leverage advantages of terminals over personal computers.

In a GUI environment, likesuch as the [[X Window System]], the display can show multiple programs {{endash}} each in its own window {{endash}} rather than a single stream of text associated with a single program. As a terminal emulator runs in a GUI environment to provide command-line access, it alleviates the need for a physical terminal and allows for multiple windows running separate emulators.

Since the advent and subsequent popularization of the [[personal computer]], few genuine hardware terminals are used to interface with computers today. Using the [[Computer monitor|monitor]] and [[Computer keyboard|keyboard]], modern operating systems like [[Linux]] and the [[Berkeley Software Distribution|BSD]] derivatives feature [[Virtual console (computer user-interface)|virtual consoles]], which are mostly independent from the hardware used.

In a GUI environment, like the [[X Window System]], the display can show multiple programs {{endash}} each in its own window {{endash}} rather than a single stream of text associated with a single program. As a terminal emulator runs in a GUI environment to provide command-line access, it alleviates the need for a physical terminal and allows for multiple windows running separate emulators.

== System console ==