Editing UTF-8 (section)

== History ==
{{See also|Universal Coded Character Set#History}}

The [[International Organization for Standardization]] (ISO) set out to compose a universal multi-byte character set in 1989. The draft ISO 10646 standard contained a non-required [[Addendum|annex]] called [[UTF-1]] that provided a byte stream encoding of its [[32-bit computing|32-bit]] code points. This encoding was not satisfactory on performance grounds, among other problems, and the biggest problem was probably that it did not have a clear separation between ASCII and non-ASCII: new UTF-1 tools would be backward compatible with ASCII-encoded text, but UTF-1-encoded text could confuse existing code expecting ASCII (or [[extended ASCII]]), because it could contain continuation bytes in the range {{mono|0x21}}–{{mono|0x7E}} that meant something else in ASCII, e.g., {{mono|0x2F}} for <code>/</code>, the [[Unix]] [[Path (computing)|path]] directory separator.

In July 1992, the [[X/Open]] committee XoJIG was looking for a better encoding. Dave Prosser of [[Unix System Laboratories]] submitted a proposal for one that had faster implementation characteristics and introduced the improvement that 7-bit ASCII characters would ''only'' represent themselves; multi-byte sequences would only include bytes with the high bit set. The name ''File System Safe UCS Transformation Format'' (''FSS-UTF'')<ref>{{cite web|url=https://www.unicode.org/L2/Historical/wg20-n193-fss-utf.pdf|title=File System Safe UCS&nbsp;— Transformation Format (FSS-UTF) - X/Open Preliminary Specification|website=unicode.org}}</ref> and most of the text of this proposal were later preserved in the final specification.<ref name="FSS-UTF">{{cite journal |title=Appendix F. FSS-UTF / File System Safe UCS Transformation format |journal=The Unicode Standard 1.1 |url=https://www.unicode.org/versions/Unicode1.1.0/appF.pdf |access-date=2016-06-07 |url-status=live |archive-url=https://web.archive.org/web/20160607215950/https://www.unicode.org/versions/Unicode1.1.0/appF.pdf |archive-date=2016-06-07}}</ref><ref name="Whistler_2001">{{cite web |title=FSS-UTF, UTF-2, UTF-8, and UTF-16 |author-first=Kenneth |author-last=Whistler |date=2001-06-12 |url=https://unicode.org/mail-arch/unicode-ml/y2001-m06/0318.html |access-date=2006-06-07 |url-status=live |archive-url=https://web.archive.org/web/20160607220249/https://unicode.org/mail-arch/unicode-ml/y2001-m06/0318.html |archive-date=2016-06-07 }}</ref><ref name="pikeviacambridge">{{cite web |url=https://www.cl.cam.ac.uk/~mgk25/ucs/utf-8-history.txt |title=UTF-8 history |author-first=Rob |author-last=Pike |author-link=Rob Pike |date=2003-04-30 |access-date=2012-09-07}}</ref> In August 1992, this proposal was circulated by an [[IBM]] X/Open representative to interested parties. A modification by [[Ken Thompson]] of the [[Plan 9 from Bell Labs|Plan 9 operating system]] group at [[Bell Labs]] made it [[Self-synchronizing code|self-synchronizing]], letting a reader start anywhere and immediately detect character boundaries, at the cost of being somewhat less bit-efficient than the previous proposal. It also abandoned the use of biases that prevented [[#overlong encodings|overlong encodings]].<ref name=pikeviacambridge/><ref>At that time subtraction was slower than bit logic on many computers, and speed was considered necessary for acceptance.{{citation needed|date=October 2024}}</ref> Thompson's design was outlined on September 2, 1992, on a [[placemat]] in a New Jersey diner with [[Rob Pike]]. In the following days, Pike and Thompson implemented it and updated [[Plan 9 from Bell Labs|Plan 9]] to use it throughout,<ref>{{cite book |chapter-url=https://www.cl.cam.ac.uk/~mgk25/ucs/UTF-8-Plan9-paper.pdf |chapter=Hello World or Καλημέρα κόσμε or こんにちは 世界 |title=Proceedings of the Winter 1993 USENIX Conference |first1=Rob |last1=Pike |first2=Ken |last2=Thompson |year=1993}}</ref> and then communicated their success back to X/Open, which accepted it as the specification for FSS-UTF.<ref name=pikeviacambridge/>

UTF-8 was first officially presented at the [[USENIX]] conference in [[San Diego]], from January 25 to 29, 1993.<ref>{{cite web|url=https://www.usenix.org/legacy/publications/library/proceedings/sd93/| title=USENIX Winter 1993 Conference Proceedings|website=usenix.org}}</ref> The [[Internet Engineering Task Force]] adopted UTF-8 in its Policy on Character Sets and Languages in RFC&nbsp;2277 ([[Request for Comments#Best Current Practice|<abbr title="Best Current Practice">BCP</abbr>]] 18) for future internet standards work in January 1998, replacing [[Single Byte Character Set]]s such as [[ISO/IEC 8859-1|Latin-1]] in older RFCs.<ref name="rfc2277">{{cite IETF |rfc=2277 |bcp=18 |title=IETF Policy on Character Sets and Languages |date=January 1998 |last1=Alvestrand |first1=Harald T. |author-link=Harald Alvestrand |publisher=[[Internet Engineering Task Force|IETF]]}}</ref>

In November 2003, UTF-8 was restricted by {{IETF RFC|3629}} to match the constraints of the [[UTF-16]] character encoding: explicitly prohibiting code points corresponding to the high and low surrogate characters removed <!-- 2*2^10/(2^16-2^11) --> more than 3% of the three-byte sequences, and ending at {{tt|U+10FFFF}} removed <!-- (2^21-(2^16+2^20))/(2^21-2^16) --> more than 48% of the four-byte sequences and all five- and six-byte sequences.<ref>{{cite web |author-last=Pike |author-first=Rob |author-link=Rob Pike |date=2012-09-06 |title=UTF-8 turned 20 years old yesterday |url=https://plus.google.com/u/0/101960720994009339267/posts/Rz1udTvtiMg |url-status=dead |archive-url=https://commandcenter.blogspot.com/2020/01/utf-8-turned-20-years-old-in-2012.html |archive-date=2020-01-26 |access-date=2012-09-07}}</ref>