- Great Painters
- Accounting
- Fundamentals of Law
- Marketing
- Shorthand
- Concept Cars
- Videogames
- The World of Sports

- Blogs
- Free Software
- Google
- My Computer

- PHP Language and Applications
- Wikipedia
- Windows Vista

- Education
- Masterpieces of English Literature
- American English

- English Dictionaries
- The English Language

- Medical Emergencies
- The Theory of Memory
- The Beatles
- Dances
- Microphones
- Musical Notation
- Music Instruments
- Batteries
- Nanotechnology
- Cosmetics
- Diets
- Vegetarianism and Veganism
- Christmas Traditions
- Animals

- Fruits And Vegetables


  1. Adobe Reader
  2. Adware
  3. Altavista
  4. AOL
  5. Apple Macintosh
  6. Application software
  7. Arrow key
  8. Artificial Intelligence
  9. ASCII
  10. Assembly language
  11. Automatic translation
  12. Avatar
  13. Babylon
  14. Bandwidth
  15. Bit
  16. BitTorrent
  17. Black hat
  18. Blog
  19. Bluetooth
  20. Bulletin board system
  21. Byte
  22. Cache memory
  23. Celeron
  24. Central processing unit
  25. Chat room
  26. Client
  27. Command line interface
  28. Compiler
  29. Computer
  30. Computer bus
  31. Computer card
  32. Computer display
  33. Computer file
  34. Computer games
  35. Computer graphics
  36. Computer hardware
  37. Computer keyboard
  38. Computer networking
  39. Computer printer
  40. Computer program
  41. Computer programmer
  42. Computer science
  43. Computer security
  44. Computer software
  45. Computer storage
  46. Computer system
  47. Computer terminal
  48. Computer virus
  49. Computing
  50. Conference call
  51. Context menu
  52. Creative commons
  53. Creative Commons License
  54. Creative Technology
  55. Cursor
  56. Data
  57. Database
  58. Data storage device
  59. Debuggers
  60. Demo
  61. Desktop computer
  62. Digital divide
  63. Discussion groups
  64. DNS server
  65. Domain name
  66. DOS
  67. Download
  68. Download manager
  69. DVD-ROM
  70. DVD-RW
  71. E-mail
  72. E-mail spam
  73. File Transfer Protocol
  74. Firewall
  75. Firmware
  76. Flash memory
  77. Floppy disk drive
  78. GNU
  79. GNU General Public License
  80. GNU Project
  81. Google
  82. Google AdWords
  83. Google bomb
  84. Graphics
  85. Graphics card
  86. Hacker
  87. Hacker culture
  88. Hard disk
  89. High-level programming language
  90. Home computer
  91. HTML
  92. Hyperlink
  93. IBM
  94. Image processing
  95. Image scanner
  96. Instant messaging
  97. Instruction
  98. Intel
  99. Intel Core 2
  100. Interface
  101. Internet
  102. Internet bot
  103. Internet Explorer
  104. Internet protocols
  105. Internet service provider
  106. Interoperability
  107. IP addresses
  108. IPod
  109. Joystick
  110. JPEG
  111. Keyword
  112. Laptop computer
  113. Linux
  114. Linux kernel
  115. Liquid crystal display
  116. List of file formats
  117. List of Google products
  118. Local area network
  119. Logitech
  120. Machine language
  121. Mac OS X
  122. Macromedia Flash
  123. Mainframe computer
  124. Malware
  125. Media center
  126. Media player
  127. Megabyte
  128. Microsoft
  129. Microsoft Windows
  130. Microsoft Word
  131. Mirror site
  132. Modem
  133. Motherboard
  134. Mouse
  135. Mouse pad
  136. Mozilla Firefox
  137. Mp3
  138. MPEG
  139. MPEG-4
  140. Multimedia
  141. Musical Instrument Digital Interface
  142. Netscape
  143. Network card
  144. News ticker
  145. Office suite
  146. Online auction
  147. Online chat
  148. Open Directory Project
  149. Open source
  150. Open source software
  151. Opera
  152. Operating system
  153. Optical character recognition
  154. Optical disc
  155. output
  156. PageRank
  157. Password
  158. Pay-per-click
  159. PC speaker
  160. Peer-to-peer
  161. Pentium
  162. Peripheral
  163. Personal computer
  164. Personal digital assistant
  165. Phishing
  166. Pirated software
  167. Podcasting
  168. Pointing device
  169. POP3
  170. Programming language
  171. QuickTime
  172. Random access memory
  173. Routers
  174. Safari
  175. Scalability
  176. Scrollbar
  177. Scrolling
  178. Scroll wheel
  179. Search engine
  180. Security cracking
  181. Server
  182. Simple Mail Transfer Protocol
  183. Skype
  184. Social software
  185. Software bug
  186. Software cracker
  187. Software library
  188. Software utility
  189. Solaris Operating Environment
  190. Sound Blaster
  191. Soundcard
  192. Spam
  193. Spamdexing
  194. Spam in blogs
  195. Speech recognition
  196. Spoofing attack
  197. Spreadsheet
  198. Spyware
  199. Streaming media
  200. Supercomputer
  201. Tablet computer
  202. Telecommunications
  203. Text messaging
  204. Trackball
  205. Trojan horse
  206. TV card
  207. Unicode
  208. Uniform Resource Identifier
  209. Unix
  210. URL redirection
  211. USB flash drive
  212. USB port
  213. User interface
  214. Vlog
  215. Voice over IP
  216. Warez
  217. Wearable computer
  218. Web application
  219. Web banner
  220. Web browser
  221. Web crawler
  222. Web directories
  223. Web indexing
  224. Webmail
  225. Web page
  226. Website
  227. Wiki
  228. Wikipedia
  229. WIMP
  230. Windows CE
  231. Windows key
  232. Windows Media Player
  233. Windows Vista
  234. Word processor
  235. World Wide Web
  236. Worm
  237. XML
  238. X Window System
  239. Yahoo
  240. Zombie computer

This article is from:

All text is available under the terms of the GNU Free Documentation License: 

Computer terminal

From Wikipedia, the free encyclopedia


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. Typically it provides a text terminal interface over a serial line.


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.

 A Televideo ASCII character mode terminal made around 1982
A Televideo ASCII character mode terminal made around 1982

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.

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. 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, various Wyse models (whose Wyse 60 was a best-sellerómany are still in use), and the Tektronix 4014, but during the late 1970's there were dozens of manufacturers of terminals, many of which had incompatible command sequences. In the 1970s and early 1980s, the most common manufacturers were DEC, Wyse, Televideo, IBM, Lear-Siegler and Heath.

While early IBM PCs had single color green screens, these were not terminals. 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. Today, most PC telnet clients provide emulation of the most common terminalóthe DEC VT100.

Graphical terminals

A HP T5700 thin client, with flash memory
A HP T5700 thin client, with flash memory

Most terminals today are GUI-based, and can show a picture on the screen. A graphical client typically uses a protocol like RDP for Microsoft Windows, or X11 for Unix-terminals. The bandwidth needed depends on the protocol used, the resolution, and the colour depth.

The graphical terminals has taken over for the text based terminals most places, and in fact led to renewed interest in thin clients.

The X11 display system for Unix is built around a server/client architecture, and was one of the first possibilities for transporting graphical applications over a network, or later, the Internet.


Further information: Text terminal

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, 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. 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.

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 n last lines are visible. The input text is buffered until the Enter key is pressed, so the application receives a ready string of text. In this mode, the application needs not to 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 shells.

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. 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).

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 ó 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. Unfortunately, the libraries, the databases and the terminal emulators themselves are too often buggy, so it is not unusual to see the display imperfect or garbled, or functional keys not working. Often it is necessary to hand-edit the terminfo definition to make a terminal emulator to work well. Perhaps things are the best with xterm, because it is the most used.

All this has led to little usability of many text-mode applications except when on console or in xterm.

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.

See also

  • Terminal server
  • IBM 3270 Classic corporate terminal for forms
  • HP 2640 microprocessor based terminal which combined serial ASCII with block mode forms and labeled function keys
  • Tektronix 4014 storage tube for vector graphics
  • VT100 for a classic ASCII ANSI-standard video terminal
  • Dumb terminal for a computer terminal that has limited functionality
  • Text terminal for the general concept of serial computer interface
  • Terminal emulator for an application program replacing a computer terminal
  • Virtual console for a concept that permits multiple terminals on one hardware
  • Computer console for a text output device for system administration messages

External links

  • Terminal virus simulator - A tech demo that recreates the look of a corrupted dumb terminal; eye candy for veterans of older computer technology. Compatible with IBM-PC; it's clones, or GP2X via DOSBox.
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