Computer terminal: Difference between revisions

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[[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 developmentdevelopments 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.

The function of a terminal is typically confined to transcription and input of data; a device with significant local, programmable data-processing capability may be called a "smart terminal" or [[fat client]]. A terminal that depends on the host computer for its processing power is called a "[[dumb terminal]]"<ref name=DicDumb>{{cite web |website=BusinessDictionary.com |title=What is dumb terminal? definition and meaning |url=http://www.businessdictionary.com/definition/dumb-terminal.html |access-date=March 13, 2019 |archive-date=August 13, 2020 |archive-url=https://web.archive.org/web/20200813062015/http://www.businessdictionary.com/definition/dumb-terminal.html |url-status=dead }}</ref> or a [[thin client]].<ref>Thin clients came later than dumb terminals</ref><ref>the term "thin client" was coined in 1993) {{cite web |url=https://www.ft.com/content/dc70f841-54b7-3ef1-abf0-d6f32b270f76 |archive-url=https://ghostarchive.org/archive/20221210/https://www.ft.com/content/dc70f841-54b7-3ef1-abf0-d6f32b270f76 |archive-date=December 10, 2022 |url-access=subscription |url-status=live |title=Is this, finally, the thin client from Oracle? |date=June 2, 2009 |first=Richard |last=Waters}}</ref> In the era of serial ([[RS-232]]) terminals there was a conflicting usage of the term "smart terminal" as a dumb terminal with no user-accessible local computing power but a particularly rich set of control codes for manipulating the display; this conflict was not resolved before hardware serial terminals became obsolete.

The use of terminals decreased over time as computing shifted from [[command line interface]] (CLI) to [[graphical user interface]] (GUI) and from [[time-sharing]] on large computers to personal computers and [[handheld device]]s. Today, users generally interact with a server over high-speed networks using a [[Web browser]] and other network-enabled GUI applications. Today, a [[terminal emulator]] application provides the capabilities of a physical terminal {{endash}} allowing interaction with the [[operating system]] [[Shell (computing)|shell]] and other CLI applications.

A personal computer can run [[terminal emulator]] software that replicates functions of a real-world terminal, sometimes allowing concurrent use of local programs and access to a distant ''terminal host'' system, either over a direct serial connection or over a network using, e.g., [[SSH]]. Today few if any dedicated computer terminals are being manufactured, as time sharing on large computers has been replaced by personal computers, handheld devices and workstations with graphical user interfaces. User interactions with servers use either software such as [[Web browsers]], or terminal emulators, with connections over high-speed networks.

==History==

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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]]]]

Two early landmarks in the development of the VDU were the [[Univac Uniscope]]<ref>{{cite web|url=https://archive.computerhistory.org/resources/text/Remington_Rand/UNIVAC.UNISCOPE_300.ca1960.102646317.pdf | title=Uniscope brochure|access-date=2021-05-23}}</ref><ref>{{cite manual

| title = Uniscope 100 - Display Terminal - General Description

| id = UP-7701

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*[[Burroughs Corporation]] TD-830

*[[AT&T]] Dataspeed 40 (3270 clone manufactured by [[Teletype Corporation]])

*[[TeleVideo]] 912,/920, /925, /950<ref>{{cite news|title=Already over 80,000 winners out there! (advertisement)|url=https://books.google.com/books?id=rx3ssrOcCTkC&q=%22block+mode+terminal%22&pg=RA1-PA6|access-date=November 27, 2012|newspaper=Computerworld|date=January 18, 1982}}</ref>

*[[Tandem Computers]] VT6530

*[[Hewlett-Packard]] [[HP 2640|VT2640]]<ref>{{cite news|title=HP 3000s, IBM CPUs Get On-Line Link|url=https://books.google.com/books?id=Z62ZAojaNzYC&q=%22block+mode+terminal%22&pg=PA35|access-date=November 27, 2012|newspaper=Computerworld|date=March 24, 1980}}</ref>

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|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}}

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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:

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===Contemporary===

{{Unreferenced section|date=May 2023}}

WhileEven though the early [[IBM Personal Computer|IBM PCsPC]] hadlooked single-colorsomewhat [[Green-screenlike display|greena screens]],terminal these screens were not terminals. The ''screen'' ofwith a PCgreen did not contain any character generation hardware; all video signals and video formatting were generated by the ''video display card'' in the PC, or (in most graphics modes) by the CPU and software. An IBM PC[[monochrome monitor]], whether it wasis thenot greenclassified monochromea displayterminal orsince theit 16-colorprovides display,local wascomputing technicallyinstead muchof moreinteracting similarwith toa anserver analog [[television set|TV set]] (withoutat a tuner)character than to a terminallevel. With suitable [[terminal emulator|software]] software, a PC couldcan, however, emulateprovide athe terminal,function andof ina thatterminal capacityto itinteract could be connected towith a mainframe or minicomputer. The [[Data General/One]] could be booted into terminal emulator mode from its ROM. Eventually microprocessor-based, personal computers greatly reduced the market demand for conventional terminals.

In the 1990s especially, "thin clients" and [[X terminal]]s have combined economical local processing power with central, shared computer facilities to retain some of the advantages of terminals over personal computers:

Today, most PC [[telnet]] clients provide emulation of the most common terminal,{{cn|date=April 2024}} the DEC VT100, using the [[ANSI escape code]] standard X3.64, or could run as X terminals using software such as [[Cygwin/X]] under [[Microsoft Windows]] or [[X.Org Server]] software under Linux.

In and around the 1990s especially, "''thin clients"client'' and [[X terminal]]s havetechnology combined the relatively economical local processing power with central, shared computer facilities to retain some of theleverage advantages of terminals over personal computers:.

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.

When usingIn a [[graphicalGUI userenvironment, interface]] (or GUI)such likeas the [[X Window System]], one'sthe display iscan typicallyshow occupiedmultiple byprograms a{{endash}} collectioneach ofin windowsits associatedown withwindow various applications,{{endash}} rather than a single stream of text associated with a single processprogram. In this case, one may useAs a terminal emulator applicationruns withinin thea windowingGUI environment. Thisto arrangementprovide permits terminal-like interaction with the computer (for running a [[command-line interpreter]]access, for example)it withoutalleviates the need for a physical terminal device;and itallows canfor evenmultiple runwindows multiplerunning terminalseparate emulators on the same device.

== System console ==

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{{Commons category|Data terminals}}

* [http://terminals-wiki.org/ The Terminals Wiki], an encyclopedia of computer terminals.

* [http://tldp.org/HOWTO/Text-Terminal-HOWTO.html Text Terminal HOWTO] from tldp.org

* [http://www.linusakesson.net/programming/tty/index.php The TTY demystified] from linussakesson.net

* {{webarchive |url=https://web.archive.org/web/20100523190056/http://www.cs.utk.edu/~shuford/terminal |date=May 23, 2010 |title=Video Terminal Information }}

* [http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:31999L0005:EN:NOT Directive 1999/5/EC of the European Parliament and of the Council of 9 March 1999 on radio equipment and telecommunications terminal equipment and the mutual recognition of their conformity (R&TTE Directive)]

* [http://www.epocalc.net/php/liste_models.php?texte=&look=All+fields&yearmax=2018&nocomp=pc&cat=Terminal epocalc listList of Computer Terminals] from epocalc.net

* [https://invisible-island.net/vttest/ VTTEST – VT100/VT220/XTerm test utility] {{dash}} A terminal test utility by Thomas E. Dickey

[[Category:Computer terminals| ]]