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A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system. Typical PC hardware A typical Personal computer consists of a case or chassis in a tower shape (desktop and the following parts Motherboard A computer is a Machine that manipulates data according to a list of instructions. Computing is usually defined like the activity of using and developing Computer technology Computer hardware and software. A computer terminal is an instance of a human-machine interface (HMI). The user interface (or Human Computer Interface) is the aggregate of means by which people&mdash the users '&mdash interact with the System

The function of a terminal is confined to display and input of data; a device with significant local programmable data processing capability may be called a "smart terminal" or thin client. A thin client (sometimes also called a lean or slim client) is a client computer or client software in Client-server architecture networks A personal computer can run software that emulates the function of a terminal, sometimes allowing concurrent use of local programs and access to a distant host system.

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Historical

ASR33 teleprinter
ASR33 teleprinter

Early user terminals connected to computers were generally electromechanical teleprinters (TTYs), such as the model 33 Teletype, originally used for telegraphy. Introduced about 1963, Teletype Corporation 's ASR33 was a very popular model of Teleprinter. A teleprinter ( Introduced about 1963, Teletype Corporation 's ASR33 was a very popular model of Teleprinter. Later printing terminals such as the DECwriter were developed. Digital Equipment Corporation was a pioneering American company in the Computer industry 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 punch cards and permit new uses for computers that would be more interactive. This article is about the Decade 1970-1979 For the Year 1970 see 1970. 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. A minicomputer (colloquially mini) is a class of multi-user Computers that lies in the middle range of the computing spectrum in between the largest Multi-user 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. Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside 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. Mostly obsolete a storage tube is a special monochromatic CRT whose screen has a kind of 'memory' (hence the name when a portion of the screen is illuminated by the CRT's Tektronix Inc is a North American company best known for its test and measurement equipment such as Oscilloscopes Logic analyzers, and video and mobile

Early video computer displays were sometimes nicknamed "Glass TTYs" and used individual logic gates, with no CPU. A logic gate performs a logical operation on one or more logic inputs and produces a single logic output One of the motivations for development of the microprocessor was to simplify and reduce the electronics required in a terminal. A microprocessor incorporates most or all of the functions of a Central processing unit (CPU on a single Integrated Most terminals were connected to mainframe computers and often had a green or amber screen. Mainframes (often colloquially referred to as Big Iron) are Computers used mainly by large organizations for critical applications typically bulk data Typically terminals communicate with the computer via a serial port, often using the RS-232 serial interface. In Computing, a serial port is a Serial communication physical interface through which information transfers in or out one Bit at a time (contrast In Telecommunications, RS-232 (Recommended Standard 232 is a standard for serial binary data signals connecting between a DTE ( Data Terminal Equipment IBM systems communicated over a coaxial cable using IBM's SNA protocol. International Business Machines Corporation abbreviated IBM and nicknamed "Big Blue", is a multinational Computer Technology Coaxial cable is a cable consisting of an inner conductor surrounded by a tubular insulating layer typically made from a flexible material with a high Dielectric constant, all Systems Network Architecture ( SNA) is IBM 's proprietary networking architecture created in 1974

A Televideo ASCII character mode terminal, using a microprocessor, circa 1982
A Televideo ASCII character mode terminal, using a microprocessor, circa 1982

Later, so-called "intelligent" terminals were introduced, such as the VT52 and VT100 made by DEC, both of which are still widely emulated in software. American Standard Code for Information Interchange ( ASCII) The VT52 was a CRT -based Computer terminal produced by Digital Equipment Corporation during the late 1970s. VT100 is a video terminal which was made by Digital Equipment Corporation (DEC Digital Equipment Corporation was a pioneering American company in the Computer industry These were called "intelligent" because they had the capability of interpreting escape sequences to position the cursor and control the display. This article refers to codes used as commands for computing devices In computing a cursor is an indicator used to show the position on a Computer monitor or other Display device that will respond to input from a text input or Notable non-VT100 computer terminal types include the IBM 3270, various Wyse models (whose Wyse 60 was a best-seller—many are still in use), and the Tektronix 4014. The IBM 3270 is a class of terminals made by IBM since 1972 (known as "display devices" normally used to communicate with IBM mainframes WYSE (970 AM) is a Radio station located in Canton North Carolina, that simulcasts WISE 's Sports talk format from Asheville The Tektronix 4014 was an early text and graphics Computer terminal based on the company's own Storage tube technology

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. Year 1970 ( MCMLXX) was a Common year starting on Thursday (link shows full calendar of the Gregorian calendar. The 1980s was the decade spanning from January 1 1980 to December 31 1989. Digital Equipment Corporation was a pioneering American company in the Computer industry WYSE (970 AM) is a Radio station located in Canton North Carolina, that simulcasts WISE 's Sports talk format from Asheville This article is about TeleVideo Corporation For information on single-unit TV/VCR devices ('televideos' see TV/VCR combo. International Business Machines Corporation abbreviated IBM and nicknamed "Big Blue", is a multinational Computer Technology The ADM-3A is one of the first Computer terminals manufactured by Lear Siegler. Heathkits were products of the Heath Company Benton Harbor Michigan.

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 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. Today, most PC telnet clients provide emulation of the most common terminal—the DEC VT100. Telnet ( Tel ecommunication net work is a Network protocol used on the Internet or local area network (LAN connections VT100 is a video terminal which was made by Digital Equipment Corporation (DEC

Text terminals

A text terminal, or often just terminal (sometimes text console) is a serial computer interface for text entry and display. Information is presented as an array of pre-selected formed characters. When such devices use a video display such as a cathode-ray tube, they are called a "video display unit" or "visual display unit" (VDU) or "video display terminal" (VDT). Video is the technology of electronically capturing, Recording, processing storing transmitting and reconstructing a sequence of Still images The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or

Original text terminals were electronic computer terminals connected to computers by a serial port, but later computers have built-in system consoles, and terminal emulator programs that work in a graphical desktop environment. In Computing, a serial port is a Serial communication physical interface through which information transfers in or out one Bit at a time (contrast The system console, root console or simply console is the text entry and display device for system administration messages particularly those from the BIOS A terminal emulator, terminal application, term, or tty for short is a program that emulates a "dumb" video terminal within some other In graphical computing a desktop environment ( DE) commonly refers to a style of Graphical user interface (GUI that is based on the Desktop metaphor which Graphical displays have not eradicated the text terminal as it is convenient for computer programmers and appropriate for command-line interfaces and text user interfaces. TUI short for Text User Interface or Textual User Interface (and sometimes Terminal User Interface) is a Retronym that was coined sometime Most programming languages support standard streams for inputting and printing text, and it is simple to connect the streams to a text terminal. In Unix and Unix-like operating systems as well as certain Programming language interfaces the standard streams are preconnected input and output channels

A typical text terminal produces input and displays output and errors
A typical text terminal produces input and displays output and errors

Types of text terminals

The System console is a text terminal used to operate a computer. The system console, root console or simply console is the text entry and display device for system administration messages particularly those from the BIOS Modern computers have a built-in keyboard and display for the console. Some Unix-like operating systems such as Linux and FreeBSD have virtual consoles to provide several text terminals on a single computer. A Unix-like (sometimes shortened to *nix) Operating system is one that behaves in a manner similar to a Unix system while not necessarily conforming Linux (commonly pronounced ˈlɪnəks FreeBSD is a Unix-like free Operating system descended from AT&T UNIX via the Berkeley Software Distribution (BSD branch through In Computing, some Operating systems such as UnixWare, Linux and BSD, feature a virtual console ( VC, sometimes

A terminal emulator is a computer program in a graphical windowing system that lets the user operate a text terminal in a window. A terminal emulator, terminal application, term, or tty for short is a program that emulates a "dumb" video terminal within some other A windowing system (or window system) is a component of a Graphical user interface (GUI and more specifically of a Desktop environment, which supports This lets text terminals coexist with modern graphical user interfaces. Popular terminal emulators include Win32 console and xterm. A terminal emulator, terminal application, term, or tty for short is a program that emulates a "dumb" video terminal within some other Win32 console is a Plain text window for Console applications within the system of Windows API. In Computing, xterm is the standard Terminal emulator for the X Window System.

There are also specialized terminal emulators such as those used with modems. PuTTY is a terminal emulator and ssh client. Putty is a generic term for a plastic material similar in texture to Clay or Dough typically used in domestic construction and repair as a sealant or filler Secure Shell or SSH is a Network protocol that allows data to be exchanged using a Secure channel between two networked devices

Applications running on a text terminal

Nano text editor running in the xterm terminal emulator
Nano text editor running in the xterm terminal emulator

The fundamental type of application running on a text terminal is a command line interpreter or shell, which prompts for commands from the user and executes each command after a press of Enter. In Computing, nano is a curses-based Text editor for Unix and Unix-like systems In Computing, xterm is the standard Terminal emulator for the X Window System. In computing a shell is a piece of software that provides an interface for users This includes Unix shells and some interactive programming environments. A Unix shell, is a command line shell that provides the traditional User interface for the Unix Operating system and for Unix-like Interactive programming is the procedure of writing parts of a program while it is already active In a shell, most of the commands are small applications themselves.

Another important application type is text editor. A text editor is a type of program used for editing plain Text files Text editors are often provided with Operating systems or software development It occupies the whole area of display, shows a text document, and allows the user to edit the document. This has in part been replaced by word processors. The first word processors used text to communicate the structure of the document, but later work outside of the text terminal and simulate the final paper document in a graphical user interface.

Programs such as Telix and Minicom control a modem and the local terminal to let the user interact with remote servers. Telix is a Telecommunications program originally written for DOS by Colin Sampaleanu and released in 1986 Minicom is a Text-based Modem control and Terminal emulation program for Unix-like operating systems originally written by Miquel Modem (from mo dulator- dem odulator is a device that modulates an analog carrier signal to encode Digital information In the Internet, telnet and ssh work similarly. The Internet is a global system of interconnected Computer networks Telnet ( Tel ecommunication net work is a Network protocol used on the Internet or local area network (LAN connections Secure Shell or SSH is a Network protocol that allows data to be exchanged using a Secure channel between two networked devices

Programming interface

In the simplest form, a text terminal is like a file. Writing to the file displays the text and reading from the file produces what the user enters. In unix-like operating systems, there are several character special files that correspond to available text terminals. A Unix-like (sometimes shortened to *nix) Operating system is one that behaves in a manner similar to a Unix system while not necessarily conforming

For other operations, there are special escape sequences, control characters and termios functions that a program can use, most easily via a library such as ncurses. This article refers to codes used as commands for computing devices In Computing and Telecommunication, a control character or non-printing character is a Code point (a Number) in a In Computing, a system call is the mechanism used by an application program to request service from the Kernel. ncurses is a programming library providing an API, allowing the programmer to write Text user interfaces in a terminal-independent manner For more complex operations, the programs can use terminal specific ioctl system calls. In computing an ioctl (aɪˈɒktəl or "i-o-control" is part of the user -to- kernel interface of a conventional operating system

Technical discussion

For an application, the simplest way to use a terminal is to simply write and read text strings to and from it sequentially. The output text is scrolled, so that only the last several lines (typically 24) are visible. Unix systems typically buffer the input text until the Enter key is pressed, so the application receives a ready string of text. Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer In Computing, a buffer is a region of memory used to temporarily hold Data while it is being moved from one place to another Originally carriage return was the term for the control character in Baudot code on a teletypewriter for end of line Return to beginning of line and In this mode, the application need not know much about the terminal.

For many interactive applications this is not sufficient. One of the common enhancements is command line editing (assisted with such libraries as readline); it also may give access to command history. GNU readline is a Software library created and maintained by the GNU Project. This is very helpful for various interactive command line interpreters.

Even more advanced interactivity is provided with full-screen applications. Those applications completely control the screen layout; also they respond to key-pressing immediately. This mode is very useful for text editors, file managers and web browsers. A text editor is a type of program used for editing plain Text files Text editors are often provided with Operating systems or software development A file manager or file browser is a Computer program that provides a User interface to work with File systems The most common operations used A web browser is a software application which enables a user to display and interact with text images videos music games and other information typically located on a In addition, such programs control the color and brightness of text on the screen, and decorate it with underline, blinking and special characters (e. g. box drawing characters). Box drawing characters, also known as line drawing characters, or pseudographics, are widely used in Text user interfaces to draw various frames and boxes

To achieve all this, the application must deal not only with plain text strings, but also with control characters and escape sequences, which allow to move cursor to an arbitrary position, to clear portions of the screen, change colors and display special characters — and also respond to function keys. In Computing and Telecommunication, a control character or non-printing character is a Code point (a Number) in a This article refers to codes used as commands for computing devices In computing a cursor is an indicator used to show the position on a Computer monitor or other Display device that will respond to input from a text input or A function key is a key on a Computer or terminal keyboard which can be programmed so as to cause an operating system command interpreter or application

The great problem here is that there are so many different terminals and terminal emulators, each with its own set of escape sequences. A terminal emulator, terminal application, term, or tty for short is a program that emulates a "dumb" video terminal within some other This article refers to codes used as commands for computing devices In order to overcome this, special libraries (such as curses) have been created, together with terminal description databases, such as Termcap and Terminfo. In Computer science, a library is a collection of Subroutines used to develop Software. curses is a terminal control library for Unix-like systems enabling the construction of text user interface (TUI applications Termcap (terminal capability is a software library and Database used on Unix-like computers Terminfo is a library and Database that enables programs to use display terminals in a device-independent manner

In recent years, the general switching of users to GUI has lessened the attention paid to terminal-handling libraries and to terminal emulation, and almost stalled the debugging efforts.

Dumb terminal

The specific meaning of the term dumb terminal can vary depending on the context in which it is used.

In the context of traditional computer terminals that communicate over a serial RS-232 connection, dumb terminals are those that can interpret a limited number of control codes (CR, LF etc. In Telecommunications, RS-232 (Recommended Standard 232 is a standard for serial binary data signals connecting between a DTE ( Data Terminal Equipment ) but do not have the ability to process special escape sequences that perform functions such as clearing a line, clearing the screen, or controlling cursor position. This article refers to codes used as commands for computing devices In computing a cursor is an indicator used to show the position on a Computer monitor or other Display device that will respond to input from a text input or In this context dumb terminals are sometimes dubbed glass teletypes, for they essentially have the same limited functionality as does a mechanical teletype. A teleprinter ( This type of dumb terminal is still supported on modern Unix-like systems by setting the environment variable TERM to dumb. A Unix-like (sometimes shortened to *nix) Operating system is one that behaves in a manner similar to a Unix system while not necessarily conforming Environment variables are a set of dynamic values that can affect the way running processes will behave on a computer Smart or intelligent terminals are those that also have the ability to process escape sequences, in particular the VT52, VT100 or ANSI escape sequences. The VT52 was a CRT -based Computer terminal produced by Digital Equipment Corporation during the late 1970s. VT100 is a video terminal which was made by Digital Equipment Corporation (DEC ANSI escape codes are used to control text formatting and other output options on Text terminals In this context ANSI refers to the ANSI X3

In the broader context that includes all forms of keyboard/screen computer communication devices, including personal computers, diskless workstations, network computers, thin clients, and X Terminals, the term dumb terminal is sometimes used to refer to any type of traditional computer terminal that communicates serially over a RS-232 connection that does not locally process data or execute user programs. A personal computer ( PC) is any Computer whose original sales price size and capabilities make it useful for individuals and which is intended to be operated A diskless node (or diskless workstation) is a Workstation or Personal computer without Disk drives which employs Network booting Network computer (abbreviated NC) is a trademark of Oracle Corporation. A thin client (sometimes also called a lean or slim client) is a client computer or client software in Client-server architecture networks In Computing, xterm is the standard Terminal emulator for the X Window System. In Telecommunications, RS-232 (Recommended Standard 232 is a standard for serial binary data signals connecting between a DTE ( Data Terminal Equipment

The term dumb terminal sometimes also refers to public computer terminals that are limited to monochrome text-only capabilities, or to terminals that transmit each character as it is typed rather than waiting until it is polled by a host computer.

Graphical terminals

A graphical terminal can display images as well as text. Graphical terminals are divided into vector-mode terminals, and raster mode. Vector graphics is the use of geometrical primitives such as points lines, Curves and shapes or Polygon (s which are all based In Computer graphics, a raster graphics image or bitmap, is a Data structure representing a generally rectangular grid of Pixels

A vector-mode display directly draws lines on the face of a cathode-ray tube under control of the host computer system. The lines are continuously formed, but since the speed of electronics is limited, the number of concurrent lines that can be displayed at one time is limited. Vector-mode displays were historically important but are no longer used.

Practically all modern graphic displays are raster-mode, descended from the picture scanning techniques used for television, in which the visual elements are a rectangular array of pixels. Television ( TV) is a widely used Telecommunication medium for sending ( Broadcasting) and receiving moving Images, either monochromatic In Digital imaging, a pixel ( pict ure el ement is the smallest piece of information in an image Since the raster image is only perceptible to the human eye as a whole for a very short time, the raster must be refreshed many times per second to give the appearance of a persistent display. The electronic demands of refreshing display memory meant that graphic terminals were developed much later than text terminals, and initially cost much more.

Most terminals today are graphical - that is, they can show images on the screen. The modern term for graphical terminal is "thin client". A thin client (sometimes also called a lean or slim client) is a client computer or client software in Client-server architecture networks A thin client typically uses a protocol like RDP for Microsoft Windows, or X11 for Unix-terminals. Remote Desktop Protocol ( RDP) is a multi-channel protocol that allows a user to connect to a computer running Microsoft Terminal Services. Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer 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 fonts (type faces). In typography a font (also fount) is traditionally defined as a complete character set of a single size and style of a particular Typeface.

Further information: Thin client

AlphaWindows

In the early 1990s an industry consortium attempted to define a standard that would allow a single CRT screen to implement multiple windows, each of which was to behave as a distinct terminal. A thin client (sometimes also called a lean or slim client) is a client computer or client software in Client-server architecture networks Unfortunately like I2O this suffered from being run as a closed standard: non-members were unable to obtain even minimal information and there was no realistic way a small company or independent developer could join the consortium, possibly because of this the standard disappeared without trace. Intelligent Input/Output (I2O is a defunct computer input/output (I/O specification

Contemporary

Since the advent and subsequent popularization of the personal computer, few genuine hardware terminals are used to interface with computers today. A personal computer ( PC) is any Computer whose original sales price size and capabilities make it useful for individuals and which is intended to be operated Using the monitor and keyboard, modern operating systems like Linux and the BSD derivatives feature virtual consoles, which are mostly independent from the hardware used. A visual display unit, often called simply a monitor or display, is a piece of Electrical equipment which displays images generated from the Video In Computing, a keyboard is an Input device partially modelled after the typewriter keyboard which uses an arrangement of buttons or keys Linux (commonly pronounced ˈlɪnəks In Computing, some Operating systems such as UnixWare, Linux and BSD, feature a virtual console ( VC, sometimes

When using a graphical user interface (or GUI) like the X Window System, one's display is typically occupied by a collection of windows associated with various applications, rather than a single stream of text associated with a single process. In this case, one may use a terminal emulator application within the windowing environment. A terminal emulator, terminal application, term, or tty for short is a program that emulates a "dumb" video terminal within some other This arrangement permits terminal-like interaction with the computer (for running a command line interpreter, for example) without the need for a physical terminal device.

See also

External links

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