109-457: ASCII ( / ˈ æ s k iː / ASS -kee ), an acronym for American Standard Code for Information Interchange , is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment , and other devices. ASCII has just 128 code points , of which only 95 are printable characters , which severely limit its scope. The set of available punctuation had significant impact on
218-402: A byte order mark or escape sequences ; compressing schemes try to minimize the number of bytes used per code unit (such as SCSU and BOCU ). Although UTF-32BE and UTF-32LE are simpler CESes, most systems working with Unicode use either UTF-8 , which is backward compatible with fixed-length ASCII and maps Unicode code points to variable-length sequences of octets, or UTF-16BE , which
327-692: A six-bit code . In a shifted code, some character codes determine choices between options for the following character codes. It allows compact encoding, but is less reliable for data transmission , as an error in transmitting the shift code typically makes a long part of the transmission unreadable. The standards committee decided against shifting, and so ASCII required at least a seven-bit code. The committee considered an eight-bit code, since eight bits ( octets ) would allow two four-bit patterns to efficiently encode two digits with binary-coded decimal . However, it would require all data transmission to send eight bits when seven could suffice. The committee voted to use
436-437: A string of the letters "ab̲c𐐀"—that is, a string containing a Unicode combining character ( U+0332 ̲ COMBINING LOW LINE ) as well as a supplementary character ( U+10400 𐐀 DESERET CAPITAL LETTER LONG I ). This string has several Unicode representations which are logically equivalent, yet while each is suited to a diverse set of circumstances or range of requirements: Note in particular that 𐐀
545-521: A BS (backspace). Instead, there was a key marked RUB OUT that sent code 127 (DEL). The purpose of this key was to erase mistakes in a manually-input paper tape: the operator had to push a button on the tape punch to back it up, then type the rubout, which punched all holes and replaced the mistake with a character that was intended to be ignored. Teletypes were commonly used with the less-expensive computers from Digital Equipment Corporation (DEC); these systems had to use what keys were available, and thus
654-546: A character encoding are known as code points and collectively comprise a code space, a code page , or character map . Early character codes associated with the optical or electrical telegraph could only represent a subset of the characters used in written languages , sometimes restricted to upper case letters , numerals and some punctuation only. The advent of digital computer systems allows more elaborate encodings codes (such as Unicode ) to support hundreds of written languages. The most popular character encoding on
763-542: A document is submitted directly for approval as a draft International Standard (DIS) to the ISO member bodies or as a final draft International Standard (FDIS), if the document was developed by an international standardizing body recognized by the ISO Council. The first step, a proposal of work (New Proposal), is approved at the relevant subcommittee or technical committee (e.g., SC 29 and JTC 1 respectively in
872-726: A line terminator. The tty driver would handle the LF to CRLF conversion on output so files can be directly printed to terminal, and NL (newline) is often used to refer to CRLF in UNIX documents. Unix and Unix-like systems, and Amiga systems, adopted this convention from Multics. On the other hand, the original Macintosh OS , Apple DOS , and ProDOS used carriage return (CR) alone as a line terminator; however, since Apple later replaced these obsolete operating systems with their Unix-based macOS (formerly named OS X) operating system, they now use line feed (LF) as well. The Radio Shack TRS-80 also used
981-683: A lone CR to terminate lines. Computers attached to the ARPANET included machines running operating systems such as TOPS-10 and TENEX using CR-LF line endings; machines running operating systems such as Multics using LF line endings; and machines running operating systems such as OS/360 that represented lines as a character count followed by the characters of the line and which used EBCDIC rather than ASCII encoding. The Telnet protocol defined an ASCII "Network Virtual Terminal" (NVT), so that connections between hosts with different line-ending conventions and character sets could be supported by transmitting
1090-442: A long process that commonly starts with the proposal of new work within a committee. Some abbreviations used for marking a standard with its status are: Abbreviations used for amendments are: Other abbreviations are: International Standards are developed by ISO technical committees (TC) and subcommittees (SC) by a process with six steps: The TC/SC may set up working groups (WG) of experts for
1199-420: A particular sequence of bits. Instead, characters would first be mapped to a universal intermediate representation in the form of abstract numbers called code points . Code points would then be represented in a variety of ways and with various default numbers of bits per character (code units) depending on context. To encode code points higher than the length of the code unit, such as above 256 for eight-bit units,
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#17327722973811308-422: A process known as transcoding . Some of these are cited below. Cross-platform : Windows : The most used character encoding on the web is UTF-8 , used in 98.2% of surveyed web sites, as of May 2024. In application programs and operating system tasks, both UTF-8 and UTF-16 are popular options. International Organization for Standardization Early research and development: Merging
1417-548: A proposal to form a new global standards body. In October 1946, ISA and UNSCC delegates from 25 countries met in London and agreed to join forces to create the International Organization for Standardization. The organization officially began operations on 23 February 1947. ISO Standards were originally known as ISO Recommendations ( ISO/R ), e.g., " ISO 1 " was issued in 1951 as "ISO/R 1". ISO
1526-436: A relatively small number of standards, ISO standards are not available free of charge, but rather for a purchase fee, which has been seen by some as unaffordable for small open-source projects. The process of developing standards within ISO was criticized around 2007 as being too difficult for timely completion of large and complex standards, and some members were failing to respond to ballots, causing problems in completing
1635-597: A reserved device control (DC0), synchronous idle (SYNC), and acknowledge (ACK). These were positioned to maximize the Hamming distance between their bit patterns. ASCII-code order is also called ASCIIbetical order. Collation of data is sometimes done in this order rather than "standard" alphabetical order ( collating sequence ). The main deviations in ASCII order are: An intermediate order converts uppercase letters to lowercase before comparing ASCII values. ASCII reserves
1744-541: A reserved meaning. Over time this interpretation has been co-opted and has eventually been changed. In modern usage, an ESC sent to the terminal usually indicates the start of a command sequence, which can be used to address the cursor, scroll a region, set/query various terminal properties, and more. They are usually in the form of a so-called " ANSI escape code " (often starting with a " Control Sequence Introducer ", "CSI", " ESC [ ") from ECMA-48 (1972) and its successors. Some escape sequences do not have introducers, like
1853-686: A seven-bit code to minimize costs associated with data transmission. Since perforated tape at the time could record eight bits in one position, it also allowed for a parity bit for error checking if desired. Eight-bit machines (with octets as the native data type) that did not use parity checking typically set the eighth bit to 0. The code itself was patterned so that most control codes were together and all graphic codes were together, for ease of identification. The first two so-called ASCII sticks (32 positions) were reserved for control characters. The "space" character had to come before graphics to make sorting easier, so it became position 20 hex ; for
1962-461: A single glyph . The former simplifies the text handling system, but the latter allows any letter/diacritic combination to be used in text. Ligatures pose similar problems. Exactly how to handle glyph variants is a choice that must be made when constructing a particular character encoding. Some writing systems, such as Arabic and Hebrew, need to accommodate things like graphemes that are joined in different ways in different contexts, but represent
2071-549: A single character per code unit. However, due to the emergence of more sophisticated character encodings, the distinction between these terms has become important. "Code page" is a historical name for a coded character set. Originally, a code page referred to a specific page number in the IBM standard character set manual, which would define a particular character encoding. Other vendors, including Microsoft , SAP , and Oracle Corporation , also published their own sets of code pages;
2180-679: A standard text format over the network. Telnet used ASCII along with CR-LF line endings, and software using other conventions would translate between the local conventions and the NVT. The File Transfer Protocol adopted the Telnet protocol, including use of the Network Virtual Terminal, for use when transmitting commands and transferring data in the default ASCII mode. This adds complexity to implementations of those protocols, and to other network protocols, such as those used for E-mail and
2289-432: A stream of octets (bytes). The purpose of this decomposition is to establish a universal set of characters that can be encoded in a variety of ways. To describe this model precisely, Unicode uses its own set of terminology to describe its process: An abstract character repertoire (ACR) is the full set of abstract characters that a system supports. Unicode has an open repertoire, meaning that new characters will be added to
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#17327722973812398-505: A well-defined and extensible encoding system, has replaced most earlier character encodings, but the path of code development to the present is fairly well known. The Baudot code, a five- bit encoding, was created by Émile Baudot in 1870, patented in 1874, modified by Donald Murray in 1901, and standardized by CCITT as International Telegraph Alphabet No. 2 (ITA2) in 1930. The name baudot has been erroneously applied to ITA2 and its many variants. ITA2 suffered from many shortcomings and
2507-736: Is 0101 in binary). Many of the non-alphanumeric characters were positioned to correspond to their shifted position on typewriters; an important subtlety is that these were based on mechanical typewriters, not electric typewriters. Mechanical typewriters followed the de facto standard set by the Remington No. 2 (1878), the first typewriter with a shift key, and the shifted values of 23456789- were "#$ %_&'() – early typewriters omitted 0 and 1 , using O (capital letter o ) and l (lowercase letter L ) instead, but 1! and 0) pairs became standard once 0 and 1 became common. Thus, in ASCII !"#$ % were placed in
2616-478: Is backward compatible with fixed-length UCS-2BE and maps Unicode code points to variable-length sequences of 16-bit words. See comparison of Unicode encodings for a detailed discussion. Finally, there may be a higher-level protocol which supplies additional information to select the particular variant of a Unicode character, particularly where there are regional variants that have been 'unified' in Unicode as
2725-637: Is "to develop worldwide Information and Communication Technology (ICT) standards for business and consumer applications." There was previously also a JTC 2 that was created in 2009 for a joint project to establish common terminology for "standardization in the field of energy efficiency and renewable energy sources". It was later disbanded. As of 2022 , there are 167 national members representing ISO in their country, with each country having only one member. ISO has three membership categories, Participating members are called "P" members, as opposed to observing members, who are called "O" members. ISO
2834-466: Is a voluntary organization whose members are recognized authorities on standards, each one representing one country. Members meet annually at a General Assembly to discuss the strategic objectives of ISO. The organization is coordinated by a central secretariat based in Geneva . A council with a rotating membership of 20 member bodies provides guidance and governance, including setting the annual budget of
2943-464: Is abused, ISO should halt the process... ISO is an engineering old boys club and these things are boring so you have to have a lot of passion ... then suddenly you have an investment of a lot of money and lobbying and you get artificial results. The process is not set up to deal with intensive corporate lobbying and so you end up with something being a standard that is not clear. International Workshop Agreements (IWAs) are documents that establish
3052-517: Is an abbreviation for "International Standardization Organization" or a similar title in another language, the letters do not officially represent an acronym or initialism . The organization provides this explanation of the name: Because 'International Organization for Standardization' would have different acronyms in different languages (IOS in English, OIN in French), our founders decided to give it
3161-521: Is approved as an International Standard (IS) if a two-thirds majority of the P-members of the TC/SC is in favour and not more than one-quarter of the total number of votes cast are negative. After approval, the document is published by the ISO central secretariat , with only minor editorial changes introduced in the publication process before the publication as an International Standard. Except for
3270-442: Is defined by a CEF. A character encoding scheme (CES) is the mapping of code units to a sequence of octets to facilitate storage on an octet-based file system or transmission over an octet-based network. Simple character encoding schemes include UTF-8 , UTF-16BE , UTF-32BE , UTF-16LE , and UTF-32LE ; compound character encoding schemes, such as UTF-16 , UTF-32 and ISO/IEC 2022 , switch between several simple schemes by using
3379-444: Is defined by the encoding. Thus, the number of code units required to represent a code point depends on the encoding: Exactly what constitutes a character varies between character encodings. For example, for letters with diacritics , there are two distinct approaches that can be taken to encode them: they can be encoded either as a single unified character (known as a precomposed character), or as separate characters that combine into
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3488-522: Is funded by a combination of: International standards are the main products of ISO. It also publishes technical reports, technical specifications, publicly available specifications, technical corrigenda (corrections), and guides. International standards Technical reports For example: Technical and publicly available specifications For example: Technical corrigenda ISO guides For example: ISO documents have strict copyright restrictions and ISO charges for most copies. As of 2020 ,
3597-430: Is preferred, usually in the larger context of locales. IBM's Character Data Representation Architecture (CDRA) designates entities with coded character set identifiers ( CCSIDs ), each of which is variously called a "charset", "character set", "code page", or "CHARMAP". The code unit size is equivalent to the bit measurement for the particular encoding: A code point is represented by a sequence of code units. The mapping
3706-425: Is produced, for example, for audio and video coding standards is called a verification model (VM) (previously also called a "simulation and test model"). When a sufficient confidence in the stability of the standard under development is reached, a working draft (WD) is produced. This is in the form of a standard, but is kept internal to working group for revision. When a working draft is sufficiently mature and
3815-426: Is replaced by a second control-S to resume output. The 33 ASR also could be configured to employ control-R (DC2) and control-T (DC4) to start and stop the tape punch; on some units equipped with this function, the corresponding control character lettering on the keycap above the letter was TAPE and TAPE respectively. The Teletype could not move its typehead backwards, so it did not have a key on its keyboard to send
3924-492: Is represented with either one 32-bit value (UTF-32), two 16-bit values (UTF-16), or four 8-bit values (UTF-8). Although each of those forms uses the same total number of bits (32) to represent the glyph, it is not obvious how the actual numeric byte values are related. As a result of having many character encoding methods in use (and the need for backward compatibility with archived data), many computer programs have been developed to translate data between character encoding schemes,
4033-617: Is restricted. The organization that is known today as ISO began in 1926 as the International Federation of the National Standardizing Associations ( ISA ), which primarily focused on mechanical engineering . The ISA was suspended in 1942 during World War II but, after the war, the ISA was approached by the recently-formed United Nations Standards Coordinating Committee (UNSCC) with
4142-404: Is the newline problem on various operating systems . Teletype machines required that a line of text be terminated with both "carriage return" (which moves the printhead to the beginning of the line) and "line feed" (which advances the paper one line without moving the printhead). The name "carriage return" comes from the fact that on a manual typewriter the carriage holding the paper moves while
4251-644: The Comité Consultatif International Téléphonique et Télégraphique (CCITT) International Telegraph Alphabet No. 2 (ITA2) standard of 1932, FIELDATA (1956), and early EBCDIC (1963), more than 64 codes were required for ASCII. ITA2 was in turn based on Baudot code , the 5-bit telegraph code Émile Baudot invented in 1870 and patented in 1874. The committee debated the possibility of a shift function (like in ITA2 ), which would allow more than 64 codes to be represented by
4360-655: The International Electrotechnical Commission . It is headquartered in Geneva , Switzerland. The three official languages of ISO are English , French , and Russian . The International Organization for Standardization in French is Organisation internationale de normalisation and in Russian, Международная организация по стандартизации ( Mezhdunarodnaya organizatsiya po standartizatsii ). Although one might think ISO
4469-636: The Teletype Model 33 , which used the left-shifted layout corresponding to ASCII, differently from traditional mechanical typewriters. Electric typewriters, notably the IBM Selectric (1961), used a somewhat different layout that has become de facto standard on computers – following the IBM PC (1981), especially Model M (1984) – and thus shift values for symbols on modern keyboards do not correspond as closely to
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4578-727: The United States Federal Government support ASCII, stating: I have also approved recommendations of the Secretary of Commerce [ Luther H. Hodges ] regarding standards for recording the Standard Code for Information Interchange on magnetic tapes and paper tapes when they are used in computer operations. All computers and related equipment configurations brought into the Federal Government inventory on and after July 1, 1969, must have
4687-604: The World Wide Web is UTF-8 , which is used in 98.2% of surveyed web sites, as of May 2024. In application programs and operating system tasks, both UTF-8 and UTF-16 are popular options. The history of character codes illustrates the evolving need for machine-mediated character-based symbolic information over a distance, using once-novel electrical means. The earliest codes were based upon manual and hand-written encoding and cyphering systems, such as Bacon's cipher , Braille , international maritime signal flags , and
4796-667: The carriage return , line feed , and tab codes. For example, lowercase i would be represented in the ASCII encoding by binary 1101001 = hexadecimal 69 ( i is the ninth letter) = decimal 105. Despite being an American standard, ASCII does not have a code point for the cent (¢). It also does not support English terms with diacritical marks such as résumé and jalapeño , or proper nouns with diacritical marks such as Beyoncé (although on certain devices characters could be combined with punctuation such as Tilde (~) and Backtick (`) to approximate such characters.) The American Standard Code for Information Interchange (ASCII)
4905-644: The "Reset to Initial State", "RIS" command " ESC c ". In contrast, an ESC read from the terminal is most often used as an out-of-band character used to terminate an operation or special mode, as in the TECO and vi text editors . In graphical user interface (GUI) and windowing systems, ESC generally causes an application to abort its current operation or to exit (terminate) altogether. The inherent ambiguity of many control characters, combined with their historical usage, created problems when transferring "plain text" files between systems. The best example of this
5014-581: The "help" prefix command in GNU Emacs . Many more of the control characters have been assigned meanings quite different from their original ones. The "escape" character (ESC, code 27), for example, was intended originally to allow sending of other control characters as literals instead of invoking their meaning, an "escape sequence". This is the same meaning of "escape" encountered in URL encodings, C language strings, and other systems where certain characters have
5123-400: The "line feed" function (which causes a printer to advance its paper), and character 8 represents " backspace ". RFC 2822 refers to control characters that do not include carriage return, line feed or white space as non-whitespace control characters. Except for the control characters that prescribe elementary line-oriented formatting, ASCII does not define any mechanism for describing
5232-486: The 1980s faced the dilemma that, on the one hand, it seemed necessary to add more bits to accommodate additional characters, but on the other hand, for the users of the relatively small character set of the Latin alphabet (who still constituted the majority of computer users), those additional bits were a colossal waste of then-scarce and expensive computing resources (as they would always be zeroed out for such users). In 1985,
5341-532: The 4-digit encoding of Chinese characters for a Chinese telegraph code ( Hans Schjellerup , 1869). With the adoption of electrical and electro-mechanical techniques these earliest codes were adapted to the new capabilities and limitations of the early machines. The earliest well-known electrically transmitted character code, Morse code , introduced in the 1840s, used a system of four "symbols" (short signal, long signal, short space, long space) to generate codes of variable length. Though some commercial use of Morse code
5450-417: The ASCII chart in this article. Ninety-five of the encoded characters are printable: these include the digits 0 to 9 , lowercase letters a to z , uppercase letters A to Z , and punctuation symbols . In addition, the original ASCII specification included 33 non-printing control codes which originated with Teletype models ; most of these are now obsolete, although a few are still commonly used, such as
5559-679: The ASCII table as earlier keyboards did. The /? pair also dates to the No. 2, and the ,< .> pairs were used on some keyboards (others, including the No. 2, did not shift , (comma) or . (full stop) so they could be used in uppercase without unshifting). However, ASCII split the ;: pair (dating to No. 2), and rearranged mathematical symbols (varied conventions, commonly -* =+ ) to :* ;+ -= . Some then-common typewriter characters were not included, notably ½ ¼ ¢ , while ^ ` ~ were included as diacritics for international use, and < > for mathematical use, together with
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#17327722973815668-468: The DEL character was assigned to erase the previous character. Because of this, DEC video terminals (by default) sent the DEL character for the key marked "Backspace" while the separate key marked "Delete" sent an escape sequence ; many other competing terminals sent a BS character for the backspace key. The early Unix tty drivers, unlike some modern implementations, allowed only one character to be set to erase
5777-741: The ETX character convention to interrupt and halt a program via an input data stream, usually from a keyboard. The Unix terminal driver uses the end-of-transmission character ( EOT ), also known as control-D, to indicate the end of a data stream. In the C programming language , and in Unix conventions, the null character is used to terminate text strings ; such null-terminated strings can be known in abbreviation as ASCIZ or ASCIIZ, where here Z stands for "zero". Other representations might be used by specialist equipment, for example ISO 2047 graphics or hexadecimal numbers. Codes 20 hex to 7E hex , known as
5886-694: The ISO Statutes. ISO was founded on 23 February 1947, and (as of July 2024 ) it has published over 25,000 international standards covering almost all aspects of technology and manufacturing. It has over 800 technical committees (TCs) and subcommittees (SCs) to take care of standards development. The organization develops and publishes international standards in technical and nontechnical fields, including everything from manufactured products and technology to food safety, transport, IT, agriculture, and healthcare. More specialized topics like electrical and electronic engineering are instead handled by
5995-469: The Teletype Model 33 machine assignments for codes 17 (control-Q, DC1, also known as XON), 19 (control-S, DC3, also known as XOFF), and 127 ( delete ) became de facto standards. The Model 33 was also notable for taking the description of control-G (code 7, BEL, meaning audibly alert the operator) literally, as the unit contained an actual bell which it rang when it received a BEL character. Because
6104-519: The Unicode standard is U+0000 to U+10FFFF, inclusive, divided in 17 planes , identified by the numbers 0 to 16. Characters in the range U+0000 to U+FFFF are in plane 0, called the Basic Multilingual Plane (BMP). This plane contains the most commonly-used characters. Characters in the range U+10000 to U+10FFFF in the other planes are called supplementary characters . The following table shows examples of code point values: Consider
6213-472: The World Wide Web, on systems not using the NVT's CR-LF line-ending convention. The PDP-6 monitor, and its PDP-10 successor TOPS-10, used control-Z (SUB) as an end-of-file indication for input from a terminal. Some operating systems such as CP/M tracked file length only in units of disk blocks, and used control-Z to mark the end of the actual text in the file. For these reasons, EOF, or end-of-file ,
6322-464: The average personal computer user's hard disk drive could store only about 10 megabytes, and it cost approximately US$ 250 on the wholesale market (and much higher if purchased separately at retail), so it was very important at the time to make every bit count. The compromise solution that was eventually found and developed into Unicode was to break the assumption (dating back to telegraph codes) that each character should always directly correspond to
6431-443: The capability to use the Standard Code for Information Interchange and the formats prescribed by the magnetic tape and paper tape standards when these media are used. Character encoding Character encoding is the process of assigning numbers to graphical characters , especially the written characters of human language, allowing them to be stored, transmitted, and transformed using computers. The numerical values that make up
6540-491: The case of MPEG, the Moving Picture Experts Group ). A working group (WG) of experts is typically set up by the subcommittee for the preparation of a working draft (e.g., MPEG is a collection of seven working groups as of 2023). When the scope of a new work is sufficiently clarified, some of the working groups may make an open request for proposals—known as a "call for proposals". The first document that
6649-418: The central secretariat. The technical management board is responsible for more than 250 technical committees , who develop the ISO standards. ISO has a joint technical committee (JTC) with the International Electrotechnical Commission (IEC) to develop standards relating to information technology (IT). Known as JTC 1 and entitled "Information technology", it was created in 1987 and its mission
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#17327722973816758-580: The change into its draft standard. The X3.2.4 task group voted its approval for the change to ASCII at its May 1963 meeting. Locating the lowercase letters in sticks 6 and 7 caused the characters to differ in bit pattern from the upper case by a single bit, which simplified case-insensitive character matching and the construction of keyboards and printers. The X3 committee made other changes, including other new characters (the brace and vertical bar characters), renaming some control characters (SOM became start of header (SOH)) and moving or removing others (RU
6867-492: The concept of "carriage return" was meaningless. IBM's PC DOS (also marketed as MS-DOS by Microsoft) inherited the convention by virtue of being loosely based on CP/M, and Windows in turn inherited it from MS-DOS. Requiring two characters to mark the end of a line introduces unnecessary complexity and ambiguity as to how to interpret each character when encountered by itself. To simplify matters, plain text data streams, including files, on Multics used line feed (LF) alone as
6976-421: The confidence people have in the standards setting process", and alleged that ISO did not carry out its responsibility. He also said that Microsoft had intensely lobbied many countries that traditionally had not participated in ISO and stacked technical committees with Microsoft employees, solution providers, and resellers sympathetic to Office Open XML: When you have a process built on trust and when that trust
7085-527: The convention was so well established that backward compatibility necessitated continuing to follow it. When Gary Kildall created CP/M , he was inspired by some of the command line interface conventions used in DEC's RT-11 operating system. Until the introduction of PC DOS in 1981, IBM had no influence in this because their 1970s operating systems used EBCDIC encoding instead of ASCII, and they were oriented toward punch-card input and line printer output on which
7194-413: The document, the draft is then approved for submission as a Final Draft International Standard (FDIS) if a two-thirds majority of the P-members of the TC/SC are in favour and if not more than one-quarter of the total number of votes cast are negative. ISO will then hold a ballot among the national bodies where no technical changes are allowed (a yes/no final approval ballot), within a period of two months. It
7303-660: The earlier five-bit ITA2 , which was also used by the competing Telex teleprinter system. Bob Bemer introduced features such as the escape sequence . His British colleague Hugh McGregor Ross helped to popularize this work – according to Bemer, "so much so that the code that was to become ASCII was first called the Bemer–Ross Code in Europe". Because of his extensive work on ASCII, Bemer has been called "the father of ASCII". On March 11, 1968, US President Lyndon B. Johnson mandated that all computers purchased by
7412-576: The earlier teleprinter encoding systems. Like other character encodings , ASCII specifies a correspondence between digital bit patterns and character symbols (i.e. graphemes and control characters ). This allows digital devices to communicate with each other and to process, store, and communicate character-oriented information such as written language. Before ASCII was developed, the encodings in use included 26 alphabetic characters, 10 numerical digits , and from 11 to 25 special graphic symbols. To include all these, and control characters compatible with
7521-543: The era had their own character codes, often six-bit, but usually had the ability to read tapes produced on IBM equipment. These BCD encodings were the precursors of IBM's Extended Binary-Coded Decimal Interchange Code (usually abbreviated as EBCDIC), an eight-bit encoding scheme developed in 1963 for the IBM System/360 that featured a larger character set, including lower case letters. In trying to develop universally interchangeable character encodings, researchers in
7630-627: The first 32 code points (numbers 0–31 decimal) and the last one (number 127 decimal) for control characters . These are codes intended to control peripheral devices (such as printers ), or to provide meta-information about data streams, such as those stored on magnetic tape. Despite their name, these code points do not represent printable characters (i.e. they are not characters at all, but signals). For debugging purposes, "placeholder" symbols (such as those given in ISO 2047 and its predecessors) are assigned to them. For example, character 0x0A represents
7739-448: The keytop for the O key also showed a left-arrow symbol (from ASCII-1963, which had this character instead of underscore ), a noncompliant use of code 15 (control-O, shift in) interpreted as "delete previous character" was also adopted by many early timesharing systems but eventually became neglected. When a Teletype 33 ASR equipped with the automatic paper tape reader received a control-S (XOFF, an abbreviation for transmit off), it caused
7848-428: The most well-known code page suites are " Windows " (based on Windows-1252) and "IBM"/"DOS" (based on code page 437 ). Despite no longer referring to specific page numbers in a standard, many character encodings are still referred to by their code page number; likewise, the term "code page" is often still used to refer to character encodings in general. The term "code page" is not used in Unix or Linux, where "charmap"
7957-721: The necessary steps within the prescribed time limits. In some cases, alternative processes have been used to develop standards outside of ISO and then submit them for its approval. A more rapid "fast-track" approval procedure was used in ISO/IEC JTC 1 for the standardization of Office Open XML (OOXML, ISO/IEC 29500, approved in April 2008), and another rapid alternative "publicly available specification" (PAS) process had been used by OASIS to obtain approval of OpenDocument as an ISO/IEC standard (ISO/IEC 26300, approved in May 2006). As
8066-619: The networks and creating the Internet: Commercialization, privatization, broader access leads to the modern Internet: Examples of Internet services: The International Organization for Standardization ( ISO / ˈ aɪ s oʊ / ) is an independent, non-governmental , international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in Article 3 of
8175-492: The next stage, called the "enquiry stage". After a consensus to proceed is established, the subcommittee will produce a draft international standard (DIS), and the text is submitted to national bodies for voting and comment within a period of five months. A document in the DIS stage is available to the public for purchase and may be referred to with its ISO DIS reference number. Following consideration of any comments and revision of
8284-411: The preparation of a working drafts. Subcommittees may have several working groups, which may have several Sub Groups (SG). It is possible to omit certain stages, if there is a document with a certain degree of maturity at the start of a standardization project, for example, a standard developed by another organization. ISO/IEC directives also allow the so-called "Fast-track procedure". In this procedure,
8393-452: The previous character in canonical input processing (where a very simple line editor is available); this could be set to BS or DEL, but not both, resulting in recurring situations of ambiguity where users had to decide depending on what terminal they were using ( shells that allow line editing, such as ksh , bash , and zsh , understand both). The assumption that no key sent a BS character allowed Ctrl+H to be used for other purposes, such as
8502-513: The previous section. Code 7F hex corresponds to the non-printable "delete" (DEL) control character and is therefore omitted from this chart; it is covered in the previous section's chart. Earlier versions of ASCII used the up arrow instead of the caret (5E hex ) and the left arrow instead of the underscore (5F hex ). ASCII was first used commercially during 1963 as a seven-bit teleprinter code for American Telephone & Telegraph 's TWX (TeletypeWriter eXchange) network. TWX originally used
8611-409: The printable characters, represent letters, digits, punctuation marks , and a few miscellaneous symbols. There are 95 printable characters in total. Code 20 hex , the "space" character, denotes the space between words, as produced by the space bar of a keyboard. Since the space character is considered an invisible graphic (rather than a control character) it is listed in the table below instead of in
8720-441: The proposed Bell code and ASCII were both ordered for more convenient sorting (i.e., alphabetization) of lists and added features for devices other than teleprinters. The use of ASCII format for Network Interchange was described in 1969. That document was formally elevated to an Internet Standard in 2015. Originally based on the (modern) English alphabet , ASCII encodes 128 specified characters into seven-bit integers as shown by
8829-412: The punched card code then in use only allowed digits, upper-case English letters and a few special characters, six bits were sufficient. These BCD encodings extended existing simple four-bit numeric encoding to include alphabetic and special characters, mapping them easily to punch-card encoding which was already in widespread use. IBM's codes were used primarily with IBM equipment; other computer vendors of
8938-460: The repertoire over time. A coded character set (CCS) is a function that maps characters to code points (each code point represents one character). For example, in a given repertoire, the capital letter "A" in the Latin alphabet might be represented by the code point 65, the character "B" by 66, and so on. Multiple coded character sets may share the same character repertoire; for example ISO/IEC 8859-1 and IBM code pages 037 and 500 all cover
9047-497: The same character. An example is the XML attribute xml:lang. The Unicode model uses the term "character map" for other systems which directly assign a sequence of characters to a sequence of bytes, covering all of the CCS, CEF and CES layers. In Unicode, a character can be referred to as 'U+' followed by its codepoint value in hexadecimal. The range of valid code points (the codespace) for
9156-520: The same reason, many special signs commonly used as separators were placed before digits. The committee decided it was important to support uppercase 64-character alphabets , and chose to pattern ASCII so it could be reduced easily to a usable 64-character set of graphic codes, as was done in the DEC SIXBIT code (1963). Lowercase letters were therefore not interleaved with uppercase . To keep options available for lowercase letters and other graphics,
9265-537: The same repertoire but map them to different code points. A character encoding form (CEF) is the mapping of code points to code units to facilitate storage in a system that represents numbers as bit sequences of fixed length (i.e. practically any computer system). For example, a system that stores numeric information in 16-bit units can only directly represent code points 0 to 65,535 in each unit, but larger code points (say, 65,536 to 1.4 million) could be represented by using multiple 16-bit units. This correspondence
9374-527: The same semantic character. Unicode and its parallel standard, the ISO/IEC 10646 Universal Character Set , together constitute a unified standard for character encoding. Rather than mapping characters directly to bytes , Unicode separately defines a coded character set that maps characters to unique natural numbers ( code points ), how those code points are mapped to a series of fixed-size natural numbers (code units), and finally how those units are encoded as
9483-490: The second stick, positions 1–5, corresponding to the digits 1–5 in the adjacent stick. The parentheses could not correspond to 9 and 0 , however, because the place corresponding to 0 was taken by the space character. This was accommodated by removing _ (underscore) from 6 and shifting the remaining characters, which corresponded to many European typewriters that placed the parentheses with 8 and 9 . This discrepancy from typewriters led to bit-paired keyboards , notably
9592-472: The short form ISO . ISO is derived from the Greek word isos ( ίσος , meaning "equal"). Whatever the country, whatever the language, the short form of our name is always ISO . During the founding meetings of the new organization, however, the Greek word explanation was not invoked, so this meaning may be a false etymology . Both the name ISO and the ISO logo are registered trademarks and their use
9701-483: The simple line characters \ | (in addition to common / ). The @ symbol was not used in continental Europe and the committee expected it would be replaced by an accented À in the French variation, so the @ was placed in position 40 hex , right before the letter A. The control codes felt essential for data transmission were the start of message (SOM), end of address (EOA), end of message (EOM), end of transmission (EOT), "who are you?" (WRU), "are you?" (RU),
9810-433: The solution was to implement variable-length encodings where an escape sequence would signal that subsequent bits should be parsed as a higher code point. Informally, the terms "character encoding", "character map", "character set" and "code page" are often used interchangeably. Historically, the same standard would specify a repertoire of characters and how they were to be encoded into a stream of code units — usually with
9919-400: The special and numeric codes were arranged before the letters, and the letter A was placed in position 41 hex to match the draft of the corresponding British standard. The digits 0–9 are prefixed with 011, but the remaining 4 bits correspond to their respective values in binary, making conversion with binary-coded decimal straightforward (for example, 5 in encoded to 011 0101 , where 5
10028-425: The standard is unclear about the meaning of "delete". Probably the most influential single device affecting the interpretation of these characters was the Teletype Model 33 ASR, which was a printing terminal with an available paper tape reader/punch option. Paper tape was a very popular medium for long-term program storage until the 1980s, less costly and in some ways less fragile than magnetic tape. In particular,
10137-440: The structure or appearance of text within a document. Other schemes, such as markup languages , address page and document layout and formatting. The original ASCII standard used only short descriptive phrases for each control character. The ambiguity this caused was sometimes intentional, for example where a character would be used slightly differently on a terminal link than on a data stream , and sometimes accidental, for example
10246-509: The subcommittee is satisfied that it has developed an appropriate technical document for the problem being addressed, it becomes a committee draft (CD) and is sent to the P-member national bodies of the SC for the collection of formal comments. Revisions may be made in response to the comments, and successive committee drafts may be produced and circulated until consensus is reached to proceed to
10355-513: The syntax of computer languages and text markup. ASCII hugely influenced the design of character sets used by modern computers, including Unicode which has over a million code points, but the first 128 of these are the same as ASCII. The Internet Assigned Numbers Authority (IANA) prefers the name US-ASCII for this character encoding. ASCII is one of the IEEE milestones . ASCII was developed in part from telegraph code . Its first commercial use
10464-441: The tape reader to stop; receiving control-Q (XON, transmit on) caused the tape reader to resume. This so-called flow control technique became adopted by several early computer operating systems as a "handshaking" signal warning a sender to stop transmission because of impending buffer overflow ; it persists to this day in many systems as a manual output control technique. On some systems, control-S retains its meaning, but control-Q
10573-447: The typebars that strike the ribbon remain stationary. The entire carriage had to be pushed (returned) to the right in order to position the paper for the next line. DEC operating systems ( OS/8 , RT-11 , RSX-11 , RSTS , TOPS-10 , etc.) used both characters to mark the end of a line so that the console device (originally Teletype machines) would work. By the time so-called "glass TTYs" (later called CRTs or "dumb terminals") came along,
10682-414: The typical cost of a copy of an ISO standard is about US$ 120 or more (and electronic copies typically have a single-user license, so they cannot be shared among groups of people). Some standards by ISO and its official U.S. representative (and, via the U.S. National Committee, the International Electrotechnical Commission ) are made freely available. A standard published by ISO/IEC is the last stage of
10791-511: Was adopted fairly widely. ASCII67's American-centric nature was somewhat addressed in the European ECMA-6 standard. Herman Hollerith invented punch card data encoding in the late 19th century to analyze census data. Initially, each hole position represented a different data element, but later, numeric information was encoded by numbering the lower rows 0 to 9, with a punch in a column representing its row number. Later alphabetic data
10900-739: Was developed under the auspices of a committee of the American Standards Association (ASA), called the X3 committee, by its X3.2 (later X3L2) subcommittee, and later by that subcommittee's X3.2.4 working group (now INCITS ). The ASA later became the United States of America Standards Institute (USASI) and ultimately became the American National Standards Institute (ANSI). With the other special characters and control codes filled in, ASCII
11009-670: Was encoded by allowing more than one punch per column. Electromechanical tabulating machines represented date internally by the timing of pulses relative to the motion of the cards through the machine. When IBM went to electronic processing, starting with the IBM 603 Electronic Multiplier, it used a variety of binary encoding schemes that were tied to the punch card code. IBM used several Binary Coded Decimal ( BCD ) six-bit character encoding schemes, starting as early as 1953 in its 702 and 704 computers, and in its later 7000 Series and 1400 series , as well as in associated peripherals. Since
11118-502: Was in the Teletype Model 33 and the Teletype Model 35 as a seven- bit teleprinter code promoted by Bell data services. Work on the ASCII standard began in May 1961, with the first meeting of the American Standards Association's (ASA) (now the American National Standards Institute or ANSI) X3.2 subcommittee. The first edition of the standard was published in 1963, underwent a major revision during 1967, and experienced its most recent update during 1986. Compared to earlier telegraph codes,
11227-409: Was often improved by many equipment manufacturers, sometimes creating compatibility issues. In 1959 the U.S. military defined its Fieldata code, a six-or seven-bit code, introduced by the U.S. Army Signal Corps. While Fieldata addressed many of the then-modern issues (e.g. letter and digit codes arranged for machine collation), it fell short of its goals and was short-lived. In 1963 the first ASCII code
11336-686: Was published as ASA X3.4-1963, leaving 28 code positions without any assigned meaning, reserved for future standardization, and one unassigned control code. There was some debate at the time whether there should be more control characters rather than the lowercase alphabet. The indecision did not last long: during May 1963 the CCITT Working Party on the New Telegraph Alphabet proposed to assign lowercase characters to sticks 6 and 7, and International Organization for Standardization TC 97 SC 2 voted during October to incorporate
11445-539: Was released (X3.4-1963) by the ASCII committee (which contained at least one member of the Fieldata committee, W. F. Leubbert), which addressed most of the shortcomings of Fieldata, using a simpler code. Many of the changes were subtle, such as collatable character sets within certain numeric ranges. ASCII63 was a success, widely adopted by industry, and with the follow-up issue of the 1967 ASCII code (which added lower-case letters and fixed some "control code" issues) ASCII67
11554-440: Was removed). ASCII was subsequently updated as USAS X3.4-1967, then USAS X3.4-1968, ANSI X3.4-1977, and finally, ANSI X3.4-1986. In the X3.15 standard, the X3 committee also addressed how ASCII should be transmitted ( least significant bit first) and recorded on perforated tape. They proposed a 9-track standard for magnetic tape and attempted to deal with some punched card formats. The X3.2 subcommittee designed ASCII based on
11663-517: Was suggested at the time by Martin Bryan, the outgoing convenor (chairman) of working group 1 (WG1) of ISO/IEC JTC 1/SC 34 , the rules of ISO were eventually tightened so that participating members that fail to respond to votes are demoted to observer status. The computer security entrepreneur and Ubuntu founder, Mark Shuttleworth , was quoted in a ZDNet blog article in 2008 about the process of standardization of OOXML as saying: "I think it de-values
11772-447: Was used colloquially and conventionally as a three-letter acronym for control-Z instead of SUBstitute. The end-of-text character ( ETX ), also known as control-C , was inappropriate for a variety of reasons, while using control-Z as the control character to end a file is analogous to the letter Z's position at the end of the alphabet, and serves as a very convenient mnemonic aid . A historically common and still prevalent convention uses
11881-590: Was via machinery, it was often used as a manual code, generated by hand on a telegraph key and decipherable by ear, and persists in amateur radio and aeronautical use. Most codes are of fixed per-character length or variable-length sequences of fixed-length codes (e.g. Unicode ). Common examples of character encoding systems include Morse code, the Baudot code , the American Standard Code for Information Interchange (ASCII) and Unicode. Unicode,
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