Encyclopedia of Computer Science and Technology

476 text editortyping commands into a Teletype or similar device. Such adevice is called a terminal.The simple early terminals did little more than acceptlines of text commands from the user and print responsesor lines of output coming from the computer. However, anewer type of terminal began to replace the Teletype. Itconsisted of a keyboard attached to a televisionlike cathoderay tube (CRT) display. User still typed commands, but thecomputer’s output could now be displayed on the screen.Gradually, CRT terminals gained additional capabilities.The text being entered was now stored in a memory bufferthat corresponded to the screen and the user could usespecial control commands or keys to move the input cursoranywhere on the screen when creating a text file. This madeit much easier for users to revise their input (see text editing).These “smart terminals” had their own small processorand ran software that provided these functions.During the 1970s, the UNIX operating system developeda sophisticated way to support the growing variety ofterminals. It provided a library of cursor-control routines(called curses) and a database of terminal characteristics(called termcap).When the personal computer came along, it had akeyboard, a processor, the ability to run software, and aconnection for a TV or monitor. The PC thus had all theingredients to become a smart terminal. Indeed, a modernPC is a terminal, but users don’t usually have to think inthose terms. The exception is when the user runs a communicationsprogram to connect to a remote computer (perhapsa bulletin board) with a modem. These programs, suchas the Hyperterminal program that comes with Windows,allow the PC to emulate (work like) one of the standard terminaltypes such as VT-100. This ability to emulate a standardterminal means that any software that supports thatphysical terminal should also work remotely with a PC.Today most interaction with remote programs is througha Web browser, although protocols such as telnet are stillused to provide terminallike access to remote programs.Many commands previously entered as text lines in a terminalare now given using the mouse with menus and icons(see user interface).The relationship between a terminal and remote computeris analogous to that between a workstation (or desktop PC)and the network server in that the burden of processing isdivided between the two devices in various ways (see clientservercomputing). A “thin client” PC performs relativelylittle processing with the server doing most of the work.Specialized terminals are still used for many applications.An ATM, for example, is a special-purpose bankingterminal driven by a keypad and touchscreen.Further ReadingArchive of Video Terminal Information. Available online. URL:http://www.cs.utk.edu/~shuford /terminal/index.html.Accessed August 22, 2007.Free Software Foundation. The Termcap Library. Available online.URL: http://www.gnu.org/manual/termcap-1.3/termcap.html.Accessed August 22, 2007.Linux Terminal Server Project. Available online. URL: http://www.ltsp.org/. Accessed August 22, 2007.text editorAs noted in the previous article (see terminal), an alternativeto batch-processing punch card driven computer operationsemerged in the 1960s in the form of text commandstyped at an interactive console or terminal. At first textcould be typed only a line at a time and there was no way tocorrect a mistake in a previous line.Soon, however, programmers began to create text editingprograms. The first editors were still line-oriented, butthey stored the lines for the current file in memory. To displaya previous line, the user might simply type its number.To correct a word in the line the user might type somethinglikec/fot/forto change the typo “fot” to the word “for” in the current line.Starting in the early 1970s, the UNIX system providedboth a line editor (ed or ex) and a “visual editor” (vi). The lattereditor works with terminals that can display full screensof text and allow the cursor to be moved anywhere on thescreen. This type of editor is also called a screen editor.Most ordinary PC users use word processors rather thantext editors to create documents. Unlike a text editor, aword processor’s features are designed to create output thatlooks as much like a printed document as possible. Thisincludes the ability to specify text fonts and styles. However,most systems also include a simpler text editor thatcan be useful for making quick notes (in Windows this programis indeed called Notepad).The primary use of text editors today is to create programsand scripts. These must generally be created usingonly standard ASCII characters (see characters andstrings), without all the embedded formatting commandsand graphics found in word processing documents. Programmer’stext editors can be very sophisticated in theirown right, providing features such as built in syntax checkingand formatting or (as with the Emacs editor) the abilityto program the editor itself. Ultimately, however, programeditors must create a source code file that can be processedby the compiler.Text editors are also useful for writing quick, shortscripts (see scripting languages) and can be handy forwriting HTML code for the Web. However, many Web pagesare now designed using word processor–like programs thatconvert the WYSIWYG (what you see is what you get) formattinginto appropriate HTML codes automatically.Further ReadingCameron, Debra, et al. Learning GNU Emacs. 3rd ed. Sebastapol,Calif.: O’Reilly, 2005.Chassell, Robert J. An Introduction to Programming in Emacs Lisp.2nd ed. Boston, Mass.: GNU Press, 2004.Robbins, Arnold, and Linda Lamb. Learning the vi Editor. 6th ed.Sebastapol, Calif.: O’Reilly, 1998.Shareware Text Editors, Word Processors, etc. Available online.URL: http://www.passtheshareware.com/c-txtwp.htm. AccessedAugust 22, 2007.Smith, Larry L. How to Use the UNIX-LINUX vi Text Editor: Tips,Tricks, and Techniques (And Tutorials Too!) Charleston, S.C.:BookSurge, 2007.