ASCII: Difference between revisions

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{{other uses}}

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{{Use mdy dates|date=June 2013|cs1-dates=y}}

| mime = us-ascii

| image = USASCII code chart.png

| lang = [[English language|English]] (made for; does not support all loanwords), [[Malay language|Malay]], [[Rotokas alphabet|Rotokas]], [[Interlingua]], [[Ido]], and [[X-SAMPA]] <!-- not Latin, see [[Apex (diacritic)]] and [[Interpunct]] -->

| extensions = * [[Unicode]]

| classification = [[ISO/IEC 646|ISO/IEC 646 series]]

}}

 

 

 

==Overview==

 

The use of ASCII format for Network Interchange was described in 1969.<ref name="RFC-20_1968">{{cite IETF |title=ASCII format for Network Interchange |rfc=20 |author-first=Vint |author-last=Cerf |author-link=Vint Cerf |date=October 16, 1969 |publisher=Network Working Group |access-date=2016-06-13}} (NB. Almost identical wording to [[USAS X3.4-1968]] except for the intro.)</ref> That document was formally elevated to an Internet Standard in 2015.<ref>{{cite web |url=https://datatracker.ietf.org/doc/status-change-rfc20-ascii-format-to-standard/ |title=Correct classification of RFC 20 (ASCII format) to Internet Standard |author=Barry Leiba |date=January 12, 2015 |publisher=[[Internet Engineering Task Force|IETF]]}}</ref>

Despite being an American standard, ASCII does not have a code point for the [[Cent (currency)|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]].

 

[[File:ASCII1963-infobox-paths.svg|thumb|upright=1.25|right|ASCII (1963). [[Control Pictures]] of equivalent controls are shown where they exist, or a grey dot otherwise.]]

The American Standard Code for Information Interchange (ASCII) 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)<ref name="Mackenzie_1980"/>{{rp|211}} and ultimately became the [[American National Standards Institute]] (ANSI).

With the other special characters and control codes filled in, ASCII was published as ASA X3.4-1963,<ref name="ASCII-1963"/><ref name="Bukstein_1964">{{cite journal |title=Binary Computer Codes and ASCII |author-first=Ed |author-last=Bukstein |journal=[[Electronics World]] |date=July 1964 |volume=72 |number=1 |pages=28–29 |url=http://www.swtpc.com/mholley/ElectronicsWorld/Jul1964/EW_Jul1964.htm |access-date=2016-05-22 |archive-url=https://web.archive.org/web/20160303180933/http://www.swtpc.com/mholley/ElectronicsWorld/Jul1964/EW_Jul1964.htm |archive-date=March 3, 2016 |url-status=dead }}</ref> leaving 28 code positions without any assigned meaning, reserved for future standardization, and one unassigned control code.<ref name="Mackenzie_1980"/>{{rp|66, 245}} There was some debate at the time whether there should be more control characters rather than the lowercase alphabet.<ref name="Mackenzie_1980"/>{{rp|435}} 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''{{Efn|name="NB_Stick"|{{anchor|Stick}}The 128 characters of the 7-bit ASCII character set are divided into eight 16-character groups called ''sticks'' 0–7, associated with the three [[most-significant bit]]s.<ref name="Bemer_1980_Inside"/> Depending on the horizontal or vertical representation of the character map, ''sticks'' can correspond with either table rows or columns.}}<ref name="Bemer_1980_Inside"/> 6 and 7,<ref name="CCITT_1963">Brief Report: Meeting of CCITT Working Party on the New Telegraph Alphabet, May 13–15, 1963.</ref> and [[International Organization for Standardization]] TC 97 SC 2 voted during October to incorporate the change into its draft standard.<ref name="ISO_1963">Report of ISO/TC/97/SC 2 – Meeting of October 29–31, 1963.</ref> The X3.2.4 task group voted its approval for the change to ASCII at its May 1963 meeting.<ref>Report on Task Group X3.2.4, June 11, 1963, Pentagon Building, Washington, DC.</ref> Locating the lowercase letters in ''sticks''{{Efn|name="NB_Stick"}}<ref name="Bemer_1980_Inside"/> 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.

 

 

 

* ASA X3.4-1965 (approved, but not published, nevertheless used by [[IBM 2260]] & [[IBM 2265|2265]] Display Stations and [[IBM 2848]] Display Control)<ref name="Mackenzie_1980"/>{{rp|423, 425–428, 435–439}}<ref name="SA_215">{{cite journal |title=Information<!-- Title of issue, not title of article --> |date=September 1966 |volume=215 |number=3 |type=special edition |journal=[[Scientific American]] |jstor=e24931041 }}</ref><ref name="Winter_2010"/><ref name="Salste_2016"/>

* ANSI X3.4-1986<ref name="ASCII-1986"/><ref name="Salste_2016"/>

* ANSI X3.4-1986 (R1992)

* ANSI X3.4-1986 (R1997)

* ANSI INCITS 4-1986 (R2002)<ref name="Korpela_2014">{{cite book |title=Unicode Explained – Internationalize Documents, Programs, and Web Sites |author-first=Jukka K. |author-last=Korpela |edition=2nd release of 1st |date=2014-03-14 |orig-year=2006-06-07 |publisher=[[O'Reilly Media, Inc.]] |isbn=978-0-596-10121-3 |page=118}}</ref>

 

In the X3.15 standard, the X3 committee also addressed how ASCII should be transmitted ([[least significant bit]] first)<ref name="Mackenzie_1980"/>{{rp|249–253}}<ref name="X3.15-1966">{{citation |title=Bit Sequencing of the American National Standard Code for Information Interchange in Serial-by-Bit Data Transmission |id=X3.15-1966 |date=1966 |publisher=[[American National Standards Institute]] (ANSI)}}</ref> and recorded on perforated tape. They proposed a [[9-track]] standard for magnetic tape and attempted to deal with some [[punched card]] formats.

 

===Bit width===

 

 

The committee debated the possibility of a [[Shift code|shift]] function (like in [[ITA2]]), which would allow more than 64 codes to be represented by a [[six-bit character code|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.<ref name="Mackenzie_1980"/>{{rp|pages=215 §13.6, 236 §4}}

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''{{Efn|name="NB_Stick"}}<ref name="Bemer_1980_Inside"/> (32 positions) were reserved for control characters.<ref name="Mackenzie_1980"/>{{rp|220, 236 8,9)}} The [[Space (punctuation)|"space" character]] had to come before graphics to make [[sorting algorithm|sorting]] easier, so it became position 20_{[[hexadecimal|hex]]};<ref name="Mackenzie_1980"/>{{rp|237 §10}} for the same reason, many special signs commonly used as separators were placed before digits. The committee decided it was important to support uppercase [[sixbit code pages|64-character alphabets]], and chose to pattern ASCII so it could be reduced easily to a usable 64-character set of graphic codes,<ref name="Mackenzie_1980"/>{{rp|228, 237 §14}} as was done in the [[DEC SIXBIT]] code (1963). [[Lower case|Lowercase]] letters were therefore not interleaved with [[uppercase]]. To keep options available for lowercase letters and other graphics, the special and numeric codes were arranged before the letters, and the letter ''A'' was placed in position 41_{[[hexadecimal|hex]]} to match the draft of the corresponding British standard.<ref name="Mackenzie_1980"/>{{rp|238 §18}} The digits 0–9 are prefixed with 011, but the remaining [[Nibble|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 is ''0101'' in binary).

 

 

Electric typewriters, notably the [[IBM Selectric]] (1961), used a somewhat different layout that has become ''de facto'' standard on computers{{snd}} following the [[IBM PC]] (1981), especially [[Model M]] (1984){{snd}} and thus shift values for symbols on modern keyboards do not correspond as closely to the ASCII table as earlier keyboards did. The <code>/?</code> pair also dates to the No. 2, and the <code>,&lt; .&gt;</code> pairs were used on some keyboards (others, including the No. 2, did not shift <code>,</code> (comma) or <code>.</code> (full stop) so they could be used in uppercase without unshifting). However, ASCII split the <code>;:</code> pair (dating to No. 2), and rearranged mathematical symbols (varied conventions, commonly <code>-* =+</code>) to <code>:* ;+ -=</code>.

==<span class="anchor" id="Code chart"></span><span class="anchor" id="ASCII printable code chart"></span><span class="anchor" id="ASCII printable characters"></span>Character set==

 

{|{{chset-table-header1|ASCII (1977/1986)}}

|-

| {{chset-ctrl1 | 25 U+0019: Control (alias END OF MEDIUM) (alias EOM) | [[End of medium|&nbsp;EM&nbsp;]] | style=background:#FFD }}

| {{chset-ctrl1 | 26 U+001A: Control (alias SUBSTITUTE) (alias SUB) | [[Substitute character|SUB]] | style=background:#FEE }}

| {{chset-ctrl1 | 28 U+001C: Control (alias INFORMATION SEPARATOR FOUR) (alias FILE SEPARATOR) (alias FS) | [[File separator|&nbsp;FS&nbsp;]] | style=background:#FFD }}

| {{chset-ctrl1 | 29 U+001D: Control (alias INFORMATION SEPARATOR THREE) (alias GROUP SEPARATOR) (alias GS) | [[Group separator|&nbsp;GS&nbsp;]] | style=background:#FFD }}

===<span class="anchor" id="ASCII control characters"></span>Control characters===

[[File:US ASCII Control Character Symbols.png|thumb|right|Early symbols assigned to the 32 control characters, space and delete characters. ([[ISO 2047]], MIL-STD-188-100, 1972)]]

ASCII reserves the first 32 [[code point]]s (numbers 0–31 decimal) and the last one (number 127 decimal) for [[control character]]s. These are codes intended to control [[peripheral device]]s (such as [[computer printer|printers]]), or to provide [[Metadata|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.

 

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 [[punched tape|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, 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 key|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 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.

 

 

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 <s>TAPE</s> respectively.<ref name="McConnell">{{cite web |title=Understanding ASCII Codes |author-last1=McConnell |author-first1=Robert |author-last2=Haynes |author-first2=James |author-last3=Warren |author-first3=Richard |url=http://www.nadcomm.com/ascii_code.htm |access-date=2014-05-11 |archive-url=https://web.archive.org/web/20140227190425/http://www.nadcomm.com/ascii_code.htm |archive-date=February 27, 2014 |url-status=dead}}</ref>

 

====Delete vs backspace====

 

The early Unix tty drivers, unlike some modern implementations, allowed only one character to be set to erase 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 ([[Shell (computing)|shells]] that allow line editing, such as [[KornShell|ksh]], [[Bash (Unix shell)|bash]], and [[Z shell|zsh]], understand both). The assumption that no key sent a BS character allowed Ctrl+H to be used for other purposes, such as the "help" prefix command in [[GNU Emacs]].<ref>{{cite web|url=https://www.gnu.org/software/emacs/manual/html_node/emacs/Help.html|title=Help - GNU Emacs Manual|access-date=July 11, 2018|archive-url=https://web.archive.org/web/20180711223750/https://www.gnu.org/software/emacs/manual/html_node/emacs/Help.html|archive-date=July 11, 2018|url-status=live}}</ref>

 

====Escape====

 

 

In contrast, an ESC read ''from'' the terminal is most often used as an [[out-of-band data|out-of-band]] character used to terminate an operation or special mode, as in the [[Text Editor and Corrector|TECO]] and [[Vi (text editor)|vi]] [[text editor]]s. In [[graphical user interface]] (GUI) and [[window (computing)|windowing]] systems, ESC generally causes an application to abort its current operation or to [[exit (system call)|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 is the [[newline]] problem on various [[operating system]]s. 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 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.

 

 

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 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,<ref>{{cite web|url=http://dosmandrivel.blogspot.com/2007/08/is-dos-rip-off-of-cpm.html|title=Is DOS a Rip-Off of CP/M?|author=Tim Paterson|date=August 8, 2007|website=DosMan Drivel|author-link=Tim Paterson|access-date=April 19, 2018|archive-url=https://web.archive.org/web/20180420075137/http://dosmandrivel.blogspot.com/2007/08/is-dos-rip-off-of-cpm.html|archive-date=April 20, 2018|url-status=live}}</ref> and [[Windows]] in turn inherited it from MS-DOS.

 

 

Computers attached to the [[ARPANET]] included machines running operating systems such as TOPS-10 and [[TENEX (operating system)|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 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.<ref name="RFC-158">{{cite IETF |title=TELNET Protocol |rfc=158 |pages=4–5 |author-first=T. |author-last=O'Sullivan |date=1971-05-19 |publisher=[[Internet Engineering Task Force]] (IETF) |access-date=2013-01-28}}</ref> 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.<ref name="RFC-542">{{cite IETF |title=File Transfer Protocol |rfc=542 |author-first=Nancy J. |author-last=Neigus |date=1973-08-12 |publisher=[[Internet Engineering Task Force]] (IETF) |access-date=2013-01-28}}</ref><ref name="RFC-765">{{cite IETF |title=File Transfer Protocol |rfc=765 |author-first=Jon |author-last=Postel |author-link=Jon Postel |date=June 1980 |publisher=[[Internet Engineering Task Force]] (IETF) |access-date=2013-01-28}}</ref> This adds complexity to implementations of those protocols, and to other network protocols, such as those used for E-mail and the World Wide Web, on systems not using the NVT's CR-LF line-ending convention.<ref>{{cite web |url=https://www.mercurial-scm.org/wiki/EOLTranslationPlan |title=EOL translation plan for Mercurial |publisher=Mercurial |access-date=2017-06-24 |archive-url=https://web.archive.org/web/20160616235536/https://www.mercurial-scm.org/wiki/EOLTranslationPlan |archive-date=June 16, 2016 |url-status=live }}</ref><ref>{{cite web |title=Bare LFs in SMTP |url=http://cr.yp.to/docs/smtplf.html |author-first=Daniel J. |author-last=Bernstein |author-link=Daniel J. Bernstein |access-date=2013-01-28 |archive-url=https://web.archive.org/web/20111029013105/http://cr.yp.to/docs/smtplf.html |archive-date=October 29, 2011 |url-status=live }}</ref>

:<code>{ a[i] = '\n'; }</code>

 

 

In Japan and Korea, still {{As of|2021|alt=as of the 2020s|post=,|df=US}} a variation of ASCII is used, in which the [[backslash]] (5C hex) is rendered as ¥ (a [[Yen sign]], in Japan) or ₩ (a [[Won sign]], in Korea). This means that, for example, the file path C:\Users\Smith is shown as C:¥Users¥Smith (in Japan) or C:₩Users₩Smith (in Korea).

{{Main|Extended ASCII}}{{See also|ISO/IEC 8859|UTF-8}}

<!-- to be mentioned [[USASCII-8]] -->

 

For some countries, 8-bit extensions of ASCII were developed that included support for characters used in local languages; for example, [[ISCII]] for India and [[VISCII]] for Vietnam. [[Kaypro]] [[CP/M]] computers used the "upper" 128 characters for the Greek alphabet.{{citation needed|date=November 2023}}

IBM defined [[code page 437]] for the [[IBM PC]], replacing the control characters with graphic symbols such as [[Emoticon|smiley faces]], and mapping additional graphic characters to the upper 128 positions.<ref>{{cite book |url=http://www.bitsavers.org/pdf/ibm/pc/pc/6025008_PC_Technical_Reference_Aug81.pdf |title=Technical Reference |at=Appendix C. Of Characters Keystrokes and Color |edition=First |date=August 1981 |series=Personal Computer Hardware Reference Library |publisher=IBM}}</ref> [[Digital Equipment Corporation]] developed the [[Multinational Character Set]] (DEC-MCS) for use in the popular [[VT220]] [[computer terminal|terminal]] as one of the first extensions designed more for international languages than for block graphics. [[Apple Inc.|Apple]] defined [[Mac OS Roman]] for the Macintosh and [[Adobe Inc.|Adobe]] defined the [[PostScript Standard Encoding]] for [[PostScript]]; both sets contained "international" letters, typographic symbols and punctuation marks instead of graphics, more like modern character sets.

 

 

[[ISO/IEC 4873]] introduced 32 additional control codes defined in the 80–9F [[hexadecimal]] range, as part of extending the 7-bit ASCII encoding to become an 8-bit system.<ref name="Unicode-5.0_2006">{{cite book |author=The Unicode Consortium |editor-first=Julie D. |editor-last=Allen |title=The Unicode standard, Version 5.0 |date=2006-10-27 |publisher=[[Addison-Wesley Professional]] |location=Upper Saddle River, New Jersey, US |isbn=978-0-321-48091-0 |chapter-url=http://unicode.org/book/ch13.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://unicode.org/book/ch13.pdf |archive-date=2022-10-09 |url-status=live |access-date=2015-03-13 |chapter=Chapter 13: Special Areas and Format Characters |page=314}}</ref>

{{cols|colwidth=30em}}

* [[3568 ASCII]] – an asteroid named after the character encoding

* [[Basic Latin (Unicode block)]] – ASCII as a subset of Unicode

* [[HTML decimal character rendering]]

* [[Jargon File]] – a glossary of computer programmer slang which includes a list of common slang names for ASCII characters

==========(PLEASE NOTE)============ -->

* {{cite web |title=C0 Controls and Basic Latin – Range: 0000–007F |work=The Unicode Standard 8.0 |date=2015 |orig-year=1991 |publisher=[[Unicode, Inc.]] |url=https://www.unicode.org/charts/PDF/U0000.pdf |access-date=2016-05-26 |url-status=live |archive-url=https://web.archive.org/web/20160526182105/http://www.unicode.org/charts/PDF/U0000.pdf |archive-date=2016-05-26}}

 

{{Character encodings|state=collapsed}}

{{Authority control}}

[[Category:ASCII| ]]

[[Category:Computer-related introductions in 1963]]