computer terminal the dec vt100 a widely emulated computer terminal ibm 2741 terminalkeyboardprinter a computer terminal is an electronic or electromechanical hardware device that is used for entering data into and displaying or printing data from a computer or a computing system early terminals were inexpensive devices but very slow compared to punched cards or paper tape for input but as the technology improved and video displays were introduced terminals pushed these older forms of interaction from the industry a related development was timesharing systems which evolved in parallel and made up for any inefficiencies of the users typing ability with the ability to support multiple users on the same machine each at their own terminal 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 fat client a terminal that depends on the host computer for its processing power is called a dumb terminal or thin client a personal computer can run terminal emulator software that replicates the function of a terminal sometimes allowing concurrent use of local programs and access to a distant terminal host system history a teletype model 33 asr teleprinter usable as a terminal the terminal of the first working programmable fully automatic digital hardcopy terminals early user terminals connected to computers were electromechanical teleprintersteletypewriters teletypewriter tty such as the teletype model 33 asr originally used for telegraphy or the friden flexowriter later printing terminals such as the decwriter la30 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 closeup of an ibm 2741 printing terminal which used a changeable selectric golfball typing element and was faster than the earlier day teletype machines by the early 1970s 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 standalone displaybased terminals it solved the memory space issue mentioned above by using a digital shiftregister design and using only 72 columns rather than the later more common choice of 80 early vdus early video computer displays were sometimes nicknamed glass ttys glass teletypes or visual display units vdus and used no cpu instead relying on individual logic gates or very primitive lsi chips nevertheless they quickly became extremely popular inputoutput devices on many different types of computer system once several suppliers gravitated to a set of common standards ascii character set rather than say ebcdic or anything specific to one company but earlyeconomy models often supported only capital letters such as the original adm3 the data general model 6052 which could be upgraded to a 6053 with a lowercase character rom and the heathkit h9 rs232 serial ports 25pin ready to connect to a modem yet some manufacturerspecific pin usage extended the standard eg for use with 20ma current loops 24 lines or possibly 25 sometimes a special status line of 80 characters of text the same as ibm punched cards later models sometimes had two characterwidth settings some type of blinking cursor that can be positioned with arrow keys or home and other direct cursor address setting codes implementation of at least 3 control codes carriage return ctrlm linefeed ctrlj and bell ctrlg but usually many more such as escape sequences to provide underlining dim or reversevideo character highlighting and especially to clear the display and position the cursor starting with the datapoint 3300 in 1969 by the late 1970s and early 1980s there were dozens of manufacturers of terminals including learsiegler adds data general dec hazeltine corporation heathzenith hewlett packard ibm televideo volkercraig and wyse many of which had incompatible command sequences although many used the early adm3 as a starting point the great variations in the control codes between makers gave rise to software that identified and grouped terminal types so the system software would correctly display input forms using the appropriate control codes in unixlike systems the termcap or terminfo files the stty utility and the term environment variable would be used in data generals business basic software for example at logintime a sequence of codes were sent to the terminal to try to read the cursors position or the 25th lines contents using a sequence of different manufacturers control code sequences and the terminalgenerated response would determine a singledigit number such as 6 for data general dasher terminals 4 for adm 3a51112 terminals 0 or 2 for ttys with no special features that would be available to programs to say which set of codes to use the great majority of terminals were monochrome manufacturers variously offering green white or amber and sometimes blue screen phosphors amber was claimed to reduce eye strain terminals with modest color capability were also available but not widely used for example a color version of the popular wyse wy50 the wy350 offered 64 shades on each character cell intelligent terminals an intelligent terminal does its own processing usually implying a microprocessor is built in but not all terminals with microprocessors did any real processing of input the main computer to which it was attached would have to respond quickly to each keystroke the term intelligent in this context dates from 1969 notable examples include the ibm 2250 and ibm 2260 predecessors to the ibm 3270 and introduced with system360 in 1964 from the introduction of the ibm 3270 and the dec vt100 1978 the user and programmer could notice significant advantages in vdu technology improvements yet not all programmers used the features of the new terminals backward compatibility in the vt100 and later televideo terminals for example with dumb terminals allowed programmers to continue to use older software some dumb terminals had been able to respond to a few escape sequences without needing microprocessors they used multiple printed circuit boards with many integrated circuits the single factor that classed a terminal as intelligent was its ability to process userinput 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 adm3a 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 blocksend capability common early uses of local processing power included features that had little to do with offloading data processing from the 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 competitors 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 screenfull of characters to be resent 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 userfriendly local editing of data and send the completed form to the main computer providing even more processing possibilities workstations like the televideo ts800 could run cpm86 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 qvt102 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 lear siegler adm3a and later models televideo 910 to 950 these models copied adm3 codes and added several of their own eventually being copied by qume and others digital equipment corporation vt52 and vt100 data general d1 to d3 and especially d200 and d210 hazeltine corporation h1500 tektronix 4014 wyse w50 w60 and w99 the ansi x364 escape code standard produced uniformity to some extent but significant differences remained for example the vt100 heathkit h19 in ansi mode televideo 970 data general d460 and qume qvt108 terminals all followed the ansi standard yet differences might exist in codes from function keys what character attributes were available blocksending of fields within forms foreign character facilities and handling of printers connected to the back of the screen most terminals were connected to minicomputers or mainframe computers and often had a green or amber screen typically terminals communicate with the computer via a serial port via a null modem cable often using an eia rs232 or rs422 or rs423 or a current loop serial interface ibm systems communicated over a coaxial cable using ibms sna protocol but for many dec data general and ncr and so on computers there were many visual display suppliers competing against the computer manufacturer for terminals to expand the systems in fact the instruction design for the intel 8008 was originally conceived at computer terminal corporation as the processor for the datapoint 2200 a televideo ascii character mode terminal using a microprocessor manufactured around 1982 contemporary 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 or in most graphics modes by the cpu and software an ibm pc monitor whether it was the green monochrome display or the 16color display was technically much more similar to an analog tv set without a tuner than to a terminal with suitable software a pc could however emulate a terminal and in that capacity it could be connected to a mainframe or minicomputer the data general one could be booted into terminal emulator mode from its rom eventually microprocessorbased personal computers greatly reduced the market demand for conventional terminals in the 1990s especially thin clients and x terminals 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 the dec vt100 using the ansi escape code standard x364 or could run as x terminals using software such as cygwinx under microsoft windows or xorg server software under linux since the advent and subsequent popularization of the personal computer few genuine hardware terminals are used to interface with computers today 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 when using a graphical user interface or gui like the x window system ones 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 this arrangement permits terminallike interaction with the computer for running a command line interpreter for example without the need for a physical terminal device it can even allow the running of multiple terminal emulators on the same device capabilities text terminals a typical text terminal produces input and displays output and errors nano text editor running in the xterm terminal emulator see also characteroriented terminal 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 preselected formed characters when such devices use a video display such as a cathoderay tube they are called a video display unit or visual display unit vdu or video display terminal vdt the system console is a text terminal used to operate a computer modern computers have a builtin keyboard and display for the console some unixlike operating systems such as linux and freebsd have virtual consoles to provide several text terminals on a single computer 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 this includes unix shells and some interactive programming environments in a shell most of the commands are small applications themselves another important application type is that of the text editor a text editor occupies the full area of display displays one or more text documents and allows the user to edit the documents the text editor has for many uses been replaced by the word processor which usually provides rich formatting features that the text editor lacks the first word processors used text to communicate the structure of the document but later word processors operate in a graphical environment and provide a wysiwyg simulation of the formatted output programs such as telix and minicom control a modem and the local terminal to let the user interact with remote servers on the internet telnet and ssh work similarly 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 unixlike operating systems there are several character special files that correspond to available text terminals 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 for more complex operations the programs can use terminal specific ioctl system calls 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 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 this is very helpful for various interactive command line interpreters even more advanced interactivity is provided with fullscreen applications those applications completely control the screen layout also they respond to keypressing immediately this mode is very useful for text editors file managers and web browsers in addition such programs control the color and brightness of text on the screen and decorate it with underline blinking and special characters eg box drawing characters 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 the great problem here is that there are so many different terminals and terminal emulators each with its own set of escape sequences in order to overcome this special libraries such as curses have been created together with terminal description databases such as termcap and terminfo dumb terminals dumb terminals are those that can interpret a limited number of control codes cr lf etc 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 in this context dumb terminals are sometimes dubbed glass teletypes for they essentially have the same limited functionality as does a mechanical teletype this type of dumb terminal is still supported on modern unixlike systems by setting the environment variable term to dumb smart or intelligent terminals are those that also have the ability to process escape sequences in particular the vt52 vt100 or ansi escape sequences graphical terminals a graphical terminal can display images as well as text graphical terminals are divided into vectormode terminals and raster mode a vectormode display directly draws lines on the face of a cathoderay 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 vectormode displays were historically important but are no longer used practically all modern graphic displays are rastermode descended from the picture scanning techniques used for television in which the visual elements are a rectangular array of pixels 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 typically uses a protocol like x11 for unixterminals or 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 fonts type faces in the early 1990s an industry consortium attempted to define a standard alphawindows that would allow a single crt screen to implement multiple windows each of which was to behave as a distinct terminal unfortunately like i2o this suffered from being run as a closed standard nonmembers 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 emulation a terminal emulator is a piece of software that emulates a text terminal in the past before the widespread use of local area networking and broadband internet access many computers would use a serial access program to communicate with other computers via telephone line or serial device when the first macintosh was released a program called macterminal was used to communicate with many computers including the ibm pc dec terminal was one of the first terminal programs for the popular altair the win32 console on windows does not emulate a physical terminal that supports escape sequences so ssh and telnet programs for logging in textually to remote computers for windows including the telnet program bundled with some versions of windows often incorporate their own code to process escape sequences the terminal emulators on most unixlike systems such as for example gnometerminal qterminal xterm terminalapp do emulate physical terminals including support for escape sequences eg xterm can emulate the vt220 and tektronix 4010 hardware terminals modes terminals can operate in various modes relating to when they send input typed by the user on the keyboard to the receiving system whatever that may be character mode aka characteratatime mode in this mode typed input is sent immediately to the receiving system line mode aka lineatatime mode in this mode the terminal provides a local line editing function and sends an entire input line after it has been locally edited when the user presses a return key block mode aka screenatatime mode in this mode the terminal provides a local fullscreen data function the user can enter input into multiple fields in a form on the screen defined to the terminal by the receiving system moving the cursor around the screen using keys such as tab and the arrow keys and performing editing functions locally using insert delete backspace and so forth the terminal sends only the completed form consisting of all the data entered on the screen to the receiving system when the user presses an enter key there is a distinction between the return and the enter keys in some multiplemode terminals that can switch between modes pressing the enter key when not in block mode does not do the same thing as pressing the return key whilst the return key will cause an input line to be sent to the host in lineatatime mode the enter key will rather cause the terminal to transmit the contents of the character row where the cursor is currently positioned to the host hostissued prompts and all different computer operating systems require different degrees of mode support when terminals are used as computer terminals the posix terminal interface as provided by unix and posixcompliant operating systems does not accommodate blockmode terminals at all and only rarely requires the terminal itself to be in lineatatime mode since the operating system is required to provide canonical input mode where the terminal device driver in the operating system emulates local echo in the terminal and performs line editing functions at the host end most usually and especially so that the host system can support noncanonical input mode terminals for posixcompliant systems are always in characteratatime mode in contrast ibm 3270 terminals connected to mvs systems are always required to be in block mode computing portal terminal server ibm 3270 ibm 5250 hp 2640 tektronix 4014 virtual console pc system console remote job entry ibm 2780 ibm 3780 tv typewriter blit computer terminal green screen display minitel thin client x terminal communication endpoint data terminal equipment end system host network node networking posix terminal interface terminal capabilities notes bangia ramesh 2010 line mode terminal dictionary of information technology laxmi publications ltd isbn9789380298153 bolthouse david 1996 exploring ibm clientserver computing business perspective series maximum press isbn9781885068040 burgess ross 1988 unix systems for microcomputers professional and industrial computing series bsp professional books isbn9780632020362 diercks jon 2002 mpeix system administration handbook hewlettpackard professional books prentice hall ptr isbn9780130305404 gofton peter w 1991 mastering unix serial communications sybex isbn9780895887085 raymond eric s 2004 the art of unix programming addisonwesley professional computing series addisonwesley isbn9780131429017 rodgers ulka 1990 unix database management systems yourdon press computing series yourdon press isbn9780139455933 topham douglas w 1990 a system v guide to unix and xenix springerverlag isbn9780387970219 wikimedia commons has media related to data terminals the terminals wiki an encyclopedia of computer terminals text terminal howto the tty demystified video terminal information at the wayback machine archived 23 may 2010 directive 19995ec 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 rtte directive epocalc list of computer terminals 