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74-455: In typesetting software, TeX Directory Structure (TDS) is a directory hierarchy for macros, fonts, and the other implementation-independent TeX system files. The top-level directories are TDS is used by several TeX distributions, including teTeX , TeX Live and MiKTeX . This free and open-source software article is a stub . You can help Misplaced Pages by expanding it . TeX TeX ( / t ɛ x / , see below ), stylized within

148-440: A DVI file ("DeVice Independent") containing the final locations of all characters. This DVI file can then be printed directly given an appropriate printer driver, or it can be converted to other formats. Nowadays, pdfTeX is often used, which bypasses DVI generation altogether. The base TeX system understands about 300 commands, called primitives . These low-level commands are rarely used directly by users, and most functionality

222-474: A Pascal subset in order to ensure readability and portability. For example, TeX does all of its dynamic allocation itself from fixed-size arrays and uses only fixed-point arithmetic for its internal calculations. As a result, TeX has been ported to almost all operating systems , usually by using the web2c program to convert the source code into C instead of directly compiling the Pascal code. Knuth has kept

296-642: A trademark for TeX. This was rejected because at the time "TEX" (all caps) was registered by Honeywell for the " Text EXecutive " text processing system. It is possible to use TeX for automatic generation of sophisticated layout for XML data. The differences in syntax between the two description languages can be overcome with the help of TeXML . In the context of XML publication, TeX can thus be considered an alternative to XSL-FO . TeX allowed scientific papers in mathematical disciplines to be reduced to relatively small files that could be rendered client-side, allowing fully typeset scientific papers to be exchanged over

370-535: A TeX-compatible engine which can directly produce PDF output (as well as continuing to support the original DVI output); XeTeX , a TeX-compatible engine that supports Unicode and OpenType ; and LuaTeX , a Unicode-aware extension to TeX that includes a Lua runtime with extensive hooks into the underlying TeX routines and algorithms. Most TeX extensions are available for free from CTAN , the Comprehensive TeX Archive Network. There are

444-624: A combined effort between people on the ITS machines at MIT and at Stanford University SAIL . The document described much of the terminology, puns, and culture of the two AI Labs and related research groups, and is the direct predecessor of the Hacker's Dictionary (1983), the first compendium of hacker jargon to be issued by a major publisher ( MIT Press ). Different implementations of ITS supported an odd array of peripherals, including an automatic wire stripper devised by hacker Richard Greenblatt, who needed

518-419: A copy of Indagationes Mathematicae , a Dutch mathematics journal. Knuth looked closely at these printed papers to sort out and look for a set of rules for spacing. While TeX provides some basic rules and the tools needed to specify proper spacing, the exact parameters depend on the font used to typeset the formula. For example, the spacing for Knuth's Computer Modern fonts has been precisely fine-tuned over

592-455: A different text syntax specifically for mathematical formulas. For example, the quadratic formula (which is the solution of the quadratic equation ) appears as: The formula is printed in a way a person would write by hand, or typeset the equation. In a document, entering mathematics mode is done by starting with a $ symbol, then entering a formula in TeX syntax, and closing again with another of

666-421: A fairly standard way to generate the actual characters to be displayed, but Knuth devotes substantial attention to the rasterizing problem on bitmapped displays. Another thesis, by John Hobby , further explores this problem of digitizing "brush trajectories". This term derives from the fact that Metafont describes characters as having been drawn by abstract brushes (and erasers). It is commonly believed that TeX

740-405: A file myfile.tex , as .tex is a common file extension for plain TeX files. By default, everything that follows a percent sign on a line is a comment, ignored by TeX. Running TeX on this file (for example, by typing tex myfile.tex in a command-line interpreter , or by calling it from a graphical user interface ) will create an output file called myfile.dvi , representing the content of

814-431: A hyphenation in the first word of a paragraph, or very overfull lines) lead to an efficient algorithm whose running time is O ( n w ) {\displaystyle O(nw)} , where w {\displaystyle w} is the width of a line. A similar algorithm is used to determine the best way to break paragraphs across two pages, in order to avoid widows or orphans (lines that appear alone on

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888-522: A line, the system will try to hyphenate a word. The original version of TeX used a hyphenation algorithm based on a set of rules for the removal of prefixes and suffixes of words, and for deciding if it should insert a break between the two consonants in a pattern of the form vowel – consonant – consonant – vowel (which is possible most of the time). TeX82 introduced a new hyphenation algorithm, designed by Frank Liang in 1983, to assign priorities to breakpoints in letter groups. A list of hyphenation patterns

962-488: A lot of attention to the spacing rules for mathematical formulae. He took three bodies of work that he considered to be standards of excellence for mathematical typography: the books typeset by the Addison-Wesley Publishing house (the publisher of The Art of Computer Programming ) under the supervision of Hans Wolf; editions of the mathematical journal Acta Mathematica dating from around 1910; and

1036-526: A major influence on the hacker culture , as described in Steven Levy's book Hackers , and were the direct forerunners of the free and open-source software , open-design , and Wiki movements. ITS development was initiated in the late 1960s by those (the majority of the MIT AI Lab staff at that time) who disagreed with the direction taken by Project MAC's Multics project (which had started in

1110-521: A page while the rest of the paragraph is on the following or preceding page). However, in general, a thesis by Michael Plass shows how the page-breaking problem can be NP-complete because of the added complication of placing figures. TeX's line-breaking algorithm has been adopted by several other programs, such as Adobe InDesign (a desktop publishing application ) and the GNU fmt Unix command line utility. If no suitable line break can be found for

1184-483: A single other character are replaced by a control-sequence token. In this sense, this stage is like lexical analysis, although it does not form numbers from digits. In the next stage, expandable control sequences (such as conditionals or defined macros) are replaced by their replacement text. The input for the third stage is then a stream of characters (including the ones with special meaning) and unexpandable control sequences (typically assignments and visual commands). Here,

1258-424: A supply of pre-stripped jumper wires of various lengths for wire-wrapping computer hardware he and others were prototyping. The device used a stepper motor and a formerly hand-held wire stripper tool and cutter, operated by solenoid , all under computer control from ITS software. The device was accessible by any ITS user, but was disappointingly unreliable in actual use. The Xerox Graphics Printer (XGP), one of

1332-467: A system associated with technical typesetting. TeX commands commonly start with a backslash and are grouped with curly braces . Almost all of TeX's syntactic properties can be changed on the fly, which makes TeX input hard to parse by anything but TeX itself. TeX is a macro - and token -based language: many commands, including most user-defined ones, are expanded on the fly until only unexpandable tokens remain, which are then executed. Expansion itself

1406-710: A user to mix texts written in left-to-right and right-to-left writing systems in the same document. In several technical fields such as computer science, mathematics, engineering and physics, TeX has become a de facto standard . Many thousands of books have been published using TeX, including books published by Addison-Wesley , Cambridge University Press , Elsevier , Oxford University Press , and Springer . Numerous journals in these fields are produced using TeX or LaTeX, allowing authors to submit their raw manuscript written in TeX. While many publications in other fields, including dictionaries and legal publications, have been produced using TeX, it has not been as successful as in

1480-465: A variety of editors designed to work with TeX : Donald Knuth has indicated several times that the source code of TeX has been placed into the " public domain ", and he strongly encourages modifications or experimentations with this source code. However, since Knuth highly values the reproducibility of the output of all versions of TeX, any changed version must not be called TeX, or anything confusingly similar. To enforce this rule, any implementation of

1554-426: A very detailed log of all the bugs he has corrected and changes he has made in the program since 1982; as of 2021 , the list contains 440 entries, not including the version modification that should be done after his death as the final change in TeX. Knuth offers monetary awards to people who find and report a bug in TeX. The award per bug started at US$ 2.56 (one "hexadecimal dollar" ) and doubled every year until it

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1628-398: Is a popular means of typesetting complex mathematical formulae ; it has been noted as one of the most sophisticated digital typographical systems. TeX is widely used in academia , especially in mathematics , computer science , economics , political science , engineering , linguistics , physics , statistics , and quantitative psychology . It has long since displaced Unix troff ,

1702-705: Is based on bitmap fonts but, in fact, these programs "know" nothing about the fonts that they are using other than their dimensions. It is the responsibility of the device driver to appropriately handle fonts of other types, including PostScript Type 1 and TrueType. Computer Modern (commonly known as "the TeX font") is freely available in Type 1 format, as are the AMS math fonts. Users of TeX systems that output directly to PDF, such as pdfTeX, XeTeX, or LuaTeX, generally never use Metafont output at all. TeX documents are written and programmed using an unusual macro language. Broadly speaking,

1776-482: Is done, as Knuth mentions in his TeXbook , to distinguish TeX from other system names such as TEX, the Text EXecutive processor (developed by Honeywell Information Systems). Fans like to proliferate names from the word "TeX"—such as TeXnician (user of TeX software), TeXhacker (TeX programmer), TeXmaster (competent TeX programmer), TeXhax , and TeXnique . Notable entities in the TeX community include

1850-478: Is first generated automatically from a corpus of hyphenated words (a list of 50,000 words). If TeX must find the acceptable hyphenation positions in the word encyclopedia , for example, it will consider all the subwords of the extended word .encyclopedia. , where . is a special marker to indicate the beginning or end of the word. The list of subwords includes all the subwords of length 1 ( . , e , n , c , y , etc.), of length 2 ( .e , en , nc , etc.), etc., up to

1924-468: Is now very stable, and only minor updates are anticipated. The current version of TeX is 3.141592653; it was last updated in 2021. The design was frozen after version 3.0, and no new feature or fundamental change will be added, so all newer versions will contain only bug fixes. Even though Donald Knuth himself has suggested a few areas in which TeX could have been improved, he indicated that he firmly believes that having an unchanged system that will produce

1998-489: Is practically free from side effects. Tail recursion of macros takes no memory, and if-then-else constructs are available. This makes TeX a Turing-complete language even at the expansion level. The system can be divided into four levels: in the first, characters are read from the input file and assigned a category code (sometimes called "catcode", for short). Combinations of a backslash (actually, any character of category zero) followed by letters (characters of category 11) or

2072-702: Is produced by the American Mathematical Society and provides many more user-friendly commands, which can be altered by journals to fit with their house style. Most of the features of AMS-TeX can be used in LaTeX by using the "AMS packages" (e.g., amsmath , amssymb ) and the "AMS document classes" (e.g., amsart , amsbook ). This is then referred to as AMS-LaTeX . Other formats include ConTeXt , used primarily for desktop publishing and written mostly by Hans Hagen at Pragma . A sample Hello world program in plain TeX is: This might be in

2146-461: Is provided by format files (predumped memory images of TeX after large macro collections have been loaded). Knuth's original default format, which adds about 600 commands, is Plain TeX. The most widely used format is LaTeX , originally developed by Leslie Lamport , which incorporates document styles for books, letters, slides, etc., and adds support for referencing and automatic numbering of sections and equations. Another widely used format, AMS-TeX ,

2220-786: Is the MiKTeX distribution (enhanced by proTeXt) and the Microsoft Windows version of TeX Live. Several document processing systems are based on TeX, notably jadeTeX , which uses TeX as a backend for printing from James Clark 's DSSSL Engine , the Arbortext publishing system, and Texinfo , the GNU documentation processing system. TeX has been the official typesetting package for the GNU operating system since 1984. Numerous extensions and companion programs for TeX exist, among them BibTeX for bibliographies (distributed with LaTeX); pdfTeX,

2294-408: Is thus the ability to work with 8-bit inputs, allowing 256 different characters in the text input. TeX3.0 was released on March 15, 1990. Since version 3, TeX has used an idiosyncratic version numbering system , where updates have been indicated by adding an extra digit at the end of the decimal, so that the version number asymptotically approaches π . This is a reflection of the fact that TeX

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2368-459: Is usually provided in the form of an easy-to-install bundle of TeX itself along with Metafont and all the necessary fonts, documents formats, and utilities needed to use the typesetting system. On UNIX-compatible systems, including Linux and Apple macOS , TeX is distributed as part of the larger TeX Live distribution. (Prior to TeX Live, the teTeX distribution was the de facto standard on UNIX-compatible systems.) On Microsoft Windows , there

2442-563: The Metafont language for font description and the Computer Modern family of typefaces ). TeX is free software , which made it accessible to a wide range of users. When the first paper volume of Knuth's The Art of Computer Programming was published in 1968, it was typeset using hot metal typesetting on a Monotype machine . This method, dating back to the 19th century, produced a "classic style" appreciated by Knuth. When

2516-563: The United Kingdom ; the user groups jointly maintain a complete list. Incompatible Timesharing System ITS, and the software developed on it, were technically and culturally influential far beyond their core user community. Remote "guest" or "tourist" access was easily available via the early ARPANET , allowing many interested parties to informally try out features of the operating system and application programs. The wide-open ITS philosophy and collaborative online community were

2590-405: The capital Greek letters tau , epsilon , and chi , as TeX is an abbreviation of τέχνη ( ΤΕΧΝΗ technē ), Greek for both "art" and "craft", which is also the root word of technical . English speakers often pronounce it / t ɛ k / , like the first syllable of technical . Knuth instructs that it be typeset with the "E" below the baseline and reduced spacing between the letters. This

2664-400: The total-fit line-breaking algorithm used by TeX and developed by Donald Knuth and Michael Plass considers all the possible breakpoints in a paragraph, and finds the combination of line breaks that will produce the most globally pleasing arrangement. Formally, the algorithm defines a value called badness associated with each possible line break; the badness is increased if the spaces on

2738-579: The TeX Users Group (TUG), which currently publishes TUGboat and formerly published The PracTeX Journal , covering a wide range of topics in digital typography relevant to TeX. The Deutschsprachige Anwendervereinigung TeX (DANTE) is a large user group in Germany. The TeX Users Group was founded in 1980 for educational and scientific purposes, provides an organization for those who have an interest in typography and font design, and are users of

2812-643: The TeX typesetting system invented by Knuth. The TeX Users Group represents the interests of TeX users worldwide. The TeX Users Group publishes the journal TUGboat three times per year; DANTE publishes Die TeXnische Komödie  [ de ] four times per year. Other user groups include DK-TUG in Denmark , GUTenberg  [ fr ] in France , GuIT in Italy , NTG in the Netherlands and UK-TUG in

2886-464: The basis of Infocom 's programming environment), and Scheme . Among other significant and influential software subsystems developed on ITS, the Macsyma symbolic algebra system, started in 1968, was the first widely-known mathematical computing environment. It was a forerunner of Maxima , MATLAB , Wolfram Mathematica , and many other computer algebra systems . Terry Winograd 's SHRDLU program

2960-429: The characters get assembled into a paragraph, and TeX's paragraph breaking algorithm works by optimizing breakpoints over the whole paragraph. The fourth stage breaks the vertical list of lines and other material into pages. The TeX system has precise knowledge of the sizes of all characters and symbols, and using this information, it computes the optimal arrangement of letters per line and lines per page. It then produces

3034-597: The concept of literate programming , a way of producing compilable source code and cross-linked documentation typeset in TeX from the same original file. The language used is called WEB and produces programs in DEC PDP-10 Pascal . TeX82, a new version of TeX rewritten from scratch, was published in 1982. Among other changes, the original hyphenation algorithm was replaced by a new algorithm written by Frank Liang . TeX82 also uses fixed-point arithmetic instead of floating-point , to ensure reproducibility of

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3108-424: The early Internet and emerging World Wide Web, even when sending large files was difficult. This paved the way for the creation of repositories of scientific papers such as arXiv , through which papers could be 'published' without an intermediary publisher. The name TeX is intended by its developer to be pronounced / t ɛ x / , with the final consonant of loch. The letters of the name are meant to represent

3182-475: The first laser printers in the world, was supported by ITS by 1974. The MIT AI Lab had one of these prototype continuous roll-fed printers for experimentation and use by its staff. By 1982, the XGP was supplemented by a Xerox Dover printer, an early sheet-fed laser printer. Although any ITS user could access the laser printers, physical access to pick up printouts was limited to staff and others who obtained access to

3256-507: The hyphens in the original dictionary; more importantly, they do not insert any spurious hyphen. In addition, a list of exceptions (words for which the patterns do not predict the correct hyphenation) are included with the Plain TeX format; additional ones can be specified by the user. Metafont, not strictly part of TeX, is a font description system which allows the designer to describe characters algorithmically. It uses Bézier curves in

3330-417: The line must stretch or shrink too much to make the line the correct width. Penalties are added if a breakpoint is particularly undesirable: for example, if a word must be hyphenated , if two lines in a row are hyphenated, or if a very loose line is immediately followed by a very tight line. The algorithm will then find the breakpoints that will minimize the sum of squares of the badness (including penalties) of

3404-428: The line. The problem is thus to find the set of breakpoints that will give the most visually pleasing result. Many line-breaking algorithms use a first-fit approach , where the breakpoints for each line are determined one after the other, and no breakpoint is changed after it has been chosen. Such a system is not able to define a breakpoint depending on the effect that it will have on the following lines. In comparison,

3478-502: The mid-1960s), particularly such decisions as the inclusion of powerful system security . The name was chosen by Tom Knight as a joke on the name of the earliest MIT time-sharing operating system, the Compatible Time-Sharing System , which dated from the early 1960s. By simplifying their system compared to Multics, ITS's authors were able to quickly produce a functional operating system for their lab. ITS

3552-548: The more technical fields, as TeX was primarily designed to typeset mathematics. When he designed TeX, Donald Knuth did not believe that a single typesetting system would fit everyone's needs; instead, he designed many hooks inside the program so that it would be possible to write extensions, and released the source code, hoping that the publishers would design versions tailoring to their own needs. While such extensions have been created (including some by Knuth himself), most people have extended TeX only using macros and it has remained

3626-422: The output of a high-quality digital typesetting system, and became interested in digital typography. On 13 May 1977, he wrote a memo to himself describing the basic features of TeX. He planned to finish it on his sabbatical in 1978, but as it happened, the language was not " frozen " (ready to use) until 1989, more than ten years later. Guy Steele happened to be at Stanford during the summer of 1978, when Knuth

3700-509: The page in a d e v ice i ndependent format (DVI). A DVI file could then be either viewed on screen or converted to a suitable format for any of the various printers for which a device driver existed (printer support was generally not an operating system feature at the time that TeX was created). Knuth has said that there is nothing inherent in TeX that requires DVI as the output format, and later versions of TeX, notably pdfTeX, XeTeX and LuaTeX, all support output directly to PDF . TeX provides

3774-430: The previously favored formatting system, in most Unix installations. It is also used for many other typesetting tasks, especially in the form of LaTeX , ConTeXt , and other macro packages. TeX was designed with two main goals in mind: to allow anybody to produce high-quality books with minimal effort, and to provide a system that would give exactly the same results on all computers, at any point in time (together with

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3848-415: The rendering of radicals has also been criticized. The OpenType math font specification largely borrows from TeX, but has some new features/enhancements. In comparison with manual typesetting, the problem of justification is easy to solve with a digital system such as TeX, which, provided that good points for line breaking have been defined, can automatically spread the spaces between words to fill in

3922-541: The resulting lines. If the paragraph contains n {\displaystyle n} possible breakpoints, the number of situations that must be evaluated naively is 2 n {\displaystyle 2^{n}} . However, by using the method of dynamic programming , the complexity of the algorithm can be brought down to O ( n 2 ) {\displaystyle O(n^{2})} (see Big O notation ). Further simplifications (for example, not testing extremely unlikely breakpoints such as

3996-424: The results across different computer hardware, and includes a real, Turing-complete programming language, following intense lobbying by Guy Steele. In 1989, Donald Knuth released new versions of TeX and Metafont . Despite his desire to keep the program stable, Knuth realised that 128 different characters for the text input were not enough to accommodate foreign languages; the main change in version 3.0 of TeX

4070-404: The running of this macro language involves expansion and execution stages which do not interact directly. Expansion includes both literal expansion of macro definitions as well as conditional branching, and execution involves such tasks as setting variables/registers and the actual typesetting process of adding glyphs to boxes. The definition of a macro not only includes a list of commands but also

4144-446: The same output now and in the future is more important than introducing new features. For this reason, he has stated that the "absolutely final change (to be made after my death)" will be to change the version number to π , at which point all remaining bugs will become features. Likewise, versions of Metafont after 2.0 asymptotically approach e (currently at 2.7182818), and a similar change will be applied after Knuth's death. Since

4218-645: The same symbol. Knuth explained in jest that he chose the dollar sign to indicate the beginning and end of mathematical mode in plain TeX because typesetting mathematics was traditionally supposed to be expensive. Display mathematics (mathematics presented centered on a new line) is similar but uses $ $ instead of a single $ symbol. For example, the above with the quadratic formula in display math: (The examples here are not actually rendered with TeX; spacing, character sizes, and all else may differ.) The TeX software incorporates several aspects that were not available, or were of lower quality, in other typesetting programs at

4292-464: The second edition was published, in 1976, the whole book had to be typeset again because the Monotype technology had been largely replaced by phototypesetting , and the original fonts were no longer available. When Knuth received the galley proofs of the new book on 30 March 1977, he found them inferior. Disappointed, Knuth set out to design his own typesetting system. Knuth saw for the first time

4366-457: The source code as long as the file is called tex.web . The copyright note at the beginning of tex.web (and mf.web) was changed in 2021 to explicitly state this. This interpretation is confirmed later in the source code when the TRIP test is mentioned ("If this program is changed, the resulting system should not be called 'TeX ' "). The American Mathematical Society tried in the early 1980s to claim

4440-524: The source code of TeX is essentially in the public domain (see below), other programmers are allowed (and explicitly encouraged) to improve the system, but are required to use another name to distribute the modified TeX, meaning that the source code can still evolve. For example, the Omega project was developed after 1991, primarily to enhance TeX's multilingual typesetting abilities. Knuth created "unofficial" modified versions, such as TeX-XeT , which allows

4514-455: The subword of length 14, which is the word itself, including the markers. TeX will then look into its list of hyphenation patterns, and find subwords for which it has calculated the desirability of hyphenation at each position. In the case of our word, 11 such patterns can be matched, namely 1 c 4 l 4 , 1 cy, 1 d 4 i 3 a, 4 edi, e 3 dia, 2 i 1 a, ope 5 d, 2 p 2 ed, 3 pedi, pedia 4 , y 1 c. For each position in

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4588-451: The syntax of the call. It differs with most widely used lexical preprocessors like M4 , in that the body of a macro gets tokenized at definition time. The TeX macro language has been used to write larger document production systems, most notably including LaTeX and ConTeXt. The original source code for the current TeX software is written in WEB , a mixture of documentation written in TeX and

4662-415: The system as T e X , is a typesetting program which was designed and written by computer scientist and Stanford University professor Donald Knuth and first released in 1978. The term now refers to the system of extensions – which includes software programs called TeX engines , sets of TeX macros , and packages which provide extra typesetting functionality – built around the original TeX language. TeX

4736-418: The system must pass a test suite called the TRIP test before being allowed to be called TeX. The question of license is somewhat confused by the statements included at the beginning of the TeX source code, which indicate that "all rights are reserved. Copying of this file is authorized only if ... you make absolutely no changes to your copy". This restriction should be interpreted as a prohibition to change

4810-416: The time when TeX was released. Some of the innovations are based on interesting algorithms, and have led to several theses for Knuth's students. While some of these discoveries have now been incorporated into other typesetting programs, others, such as the rules for mathematical spacing, are still unique. Since the primary goal of the TeX language is high-quality typesetting for publishers of books, Knuth gave

4884-573: The word, TeX will calculate the maximum value obtained among all matching patterns, yielding en 1 cy 1 c 4 l 4 o 3 p 4 e 5 d 4 i 3 a 4 . Finally, the acceptable positions are those indicated by an odd number, yielding the acceptable hyphenations en-cy-clo-pe-di-a . This system based on subwords allows the definition of very general patterns (such as 2 i 1 a), with low indicative numbers (either odd or even), which can then be superseded by more specific patterns (such as 1 d 4 i 3 a) if necessary. These patterns find about 90% of

4958-485: The years and is now set; but when other fonts, such as AMS Euler , were used by Knuth for the first time, new spacing parameters had to be defined. The typesetting of math in TeX is not without criticism, particularly with respect to technical details of the font metrics, which were designed in an era when significant attention was paid to storage requirements. This resulted in some "hacks" overloading some fields, which in turn required other "hacks". On an aesthetics level,

5032-497: Was called PEEK. The local spelling "TURIST" is an artifact of six-character filename (and other identifier) limitations, which is traceable to six SIXBIT encoded characters fitting into a single 36-bit PDP-10 word. "TURIST" may also have been a pun on Alan Turing , a pioneer of theoretical computer science . The less-complimentary term " LUSER " was also applied to guest users, especially those who repeatedly engaged in clueless or vandalous behavior. The Jargon File started as

5106-668: Was developed in ITS. The computer game Zork was also originally written on ITS. Richard Greenblatt 's Mac Hack VI was the top-rated chess program for years and was the first to display a graphical board representation. The default ITS top-level command interpreter was the PDP-10 machine language debugger ( DDT ). The usual text editor on ITS was TECO and later Emacs , which was written in TECO. Both DDT and TECO were implemented through simple dispatch tables on single-letter commands, and thus had no true syntax . The ITS task manager

5180-641: Was developing his first version of TeX. When Steele returned to the Massachusetts Institute of Technology that autumn, he rewrote TeX's input/output ( I/O ) to run under the Incompatible Timesharing System (ITS) operating system. The first version of TeX, called TeX78, was written in the SAIL programming language to run on a PDP-10 under Stanford's WAITS operating system. For later versions of TeX, Knuth invented

5254-502: Was frozen at its current value of $ 327.68. Knuth has lost relatively little money as there have been very few bugs claimed. In addition, recipients have been known to frame their check as proof that they found a bug in TeX rather than cashing it. Due to scammers finding scanned copies of his checks on the internet and using them to try to drain his bank account, Knuth no longer sends out real checks, but those who submit bug reports can get credit at The Bank of San Serriffe instead. TeX

5328-452: Was philosophically significantly different from that provided by most operating systems at the time. The wide-open ITS philosophy and collaborative community were the direct forerunner of the free and open-source software , open-design , and Wiki movements. The EMACS ("Editor MACroS") editor was originally written on ITS. In its ITS instantiation it was a collection of TECO programs (called "macros"). On later operating systems, it

5402-768: Was written in assembly language , originally for the Digital Equipment Corporation PDP-6 computer, but the majority of ITS development and use was on the later, largely compatible, PDP-10 . Although not used as intensively after about 1986, ITS continued to operate on original hardware at MIT until 1990, and then until 1995 at Stacken Computer Club in Sweden. Today, some ITS implementations continue to be remotely accessible, via emulation of PDP-10 hardware running on modern, low-cost computers supported by interested hackers. ITS introduced many then-new features: The environment seen by ITS users

5476-608: Was written in the common language of those systems – for example, the C language under Unix, and Zetalisp under the Lisp Machine system. GNU ‘s info help system was originally an EMACS subsystem, and then was later written as a complete standalone system for Unix-like machines. Several important programming languages and systems were developed on ITS, including MacLisp (the precursor of Zetalisp and Common Lisp ), Microplanner (implemented in MacLisp), MDL (which became

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