Editing Endianness (section)

{{Short description|Order of bytes in a computer word}}
{{Redirect2|Big-endian|Little-endian|the conflicting ideologies in ''Gulliver's Travels''|Lilliput and Blefuscu#History and politics}}
{{For|the specific use of endianness in date formats|Calendar date}}
{{refimprove|date=July 2020}}
[[file:Gullivers_travels.jpg|thumb|''[[Gulliver's Travels]]'' by [[Jonathan Swift]], the novel from which the term was coined]]

In [[computing]], '''endianness''' is the order in which [[byte]]s within a [[word (data type)|word]] of digital data are transmitted over a [[data communication]] medium or [[Memory_address|addressed]] (by rising addresses) in [[computer memory]], counting only byte [[Bit_numbering#Bit significance and indexing|significance]] compared to earliness. Endianness is primarily expressed as '''big-endian''' ('''BE''') or '''little-endian''' ('''LE'''), terms introduced by [[Danny Cohen (computer scientist)|Danny Cohen]] into computer science for data ordering in an [[Internet Experiment Note]] published in 1980.<ref name="HOLY">{{cite IETF | title = On Holy Wars and a Plea for Peace | ien = 137 | last = Cohen | first = Danny | author-link = Danny Cohen (computer scientist) | date = 1980-04-01 | publisher = [[IETF]] }} Also published at {{cite journal |journal=IEEE Computer |volume=14 |issue=10 |url=https://ieeexplore.ieee.org/document/1667115 |title=On Holy Wars and a Plea for Peace |last=Cohen |first=Danny |pages=48–54 |doi=10.1109/C-M.1981.220208 |date=October 1981}}</ref> The adjective ''endian'' has its origin in the writings of 18th century Anglo-Irish writer [[Jonathan Swift]]. In the 1726 novel ''[[Gulliver's Travels]]'', he portrays the conflict between sects of Lilliputians divided into those breaking the shell of a [[boiled egg]] from the big end or from the little end.<ref>{{cite book | first = Jonathan | last = Swift | title = Gulliver's Travels | chapter = A Voyage to Lilliput, Chapter IV | year = 1726 | chapter-url = https://en.wikisource.org/wiki/The_Works_of_the_Rev._Jonathan_Swift/Volume_6/A_Voyage_to_Lilliput/Chapter_4 | access-date = 2022-09-20 | archive-date = 2022-09-20 | archive-url = https://web.archive.org/web/20220920173204/https://en.wikisource.org/wiki/The_Works_of_the_Rev._Jonathan_Swift/Volume_6/A_Voyage_to_Lilliput/Chapter_4 | url-status = live }}</ref><ref>{{Citation | last1 = Bryant | first1 = Randal E. | author-link = Randal Bryant | last2 = David | first2 = O'Hallaron | title = Computer Systems: A Programmer's Perspective | publisher = Pearson Education | year = 2016 | edition = 3 | isbn = 978-1-488-67207-1 | page = 79 }}</ref> By analogy, a CPU may read a digital word big end first or little end first.

Computers store information in various-sized groups of binary bits. Each group is assigned a number, called its ''address'', that the computer uses to access that data. On most modern computers, the smallest data group with an address is eight bits long and is called a byte. Larger groups comprise two or more bytes, for example, a [[32-bit]] word contains four bytes. There are two principal ways a computer could number the individual bytes in a larger group, starting at either end. Both types of endianness are in widespread use in digital electronic engineering. The initial choice of endianness of a new design is often arbitrary, but later technology revisions and updates perpetuate the existing endianness to maintain [[backward compatibility]].

A big-endian system stores the [[most significant byte]] of a word at the smallest [[memory address]] and the [[least significant byte]] at the largest. A little-endian system, in contrast, stores the least-significant byte at the smallest address.<ref>{{Cite web |url=https://betterexplained.com/articles/understanding-big-and-little-endian-byte-order/ |title=Understanding big and little endian byte order |website=betterexplained.com |access-date=2019-05-20 |archive-date=2019-05-24 |archive-url=https://web.archive.org/web/20190524124000/https://betterexplained.com/articles/understanding-big-and-little-endian-byte-order/ |url-status=live }}</ref><ref>{{Cite web |url=https://developer.apple.com/library/archive/documentation/CoreFoundation/Conceptual/CFMemoryMgmt/Concepts/ByteOrdering.html#//apple_ref/doc/uid/20001150-CJBEJBHH |title=Byte Ordering PPC |access-date=2019-05-20 |archive-date=2019-05-09 |archive-url=https://web.archive.org/web/20190509013855/https://developer.apple.com/library/archive/documentation/CoreFoundation/Conceptual/CFMemoryMgmt/Concepts/ByteOrdering.html#//apple_ref/doc/uid/20001150-CJBEJBHH |url-status=live }}</ref><ref>{{Cite web |url=https://developer.ibm.com/articles/au-endianc/ |title=Writing endian-independent code in C |access-date=2019-05-20 |archive-date=2019-06-10 |archive-url=https://web.archive.org/web/20190610085733/https://developer.ibm.com/articles/au-endianc/ |url-status=live }}</ref> Of the two, big-endian is thus closer to the way the digits of numbers are written left-to-right in English, comparing digits to bytes. ''Bi-endianness'' is a feature supported by numerous computer architectures that feature switchable endianness in data fetches and stores or for instruction fetches. Other orderings are generically called ''middle-endian'' or ''mixed-endian''.<ref>{{cite web |title = Internet Hall of Fame Pioneer |url = http://internethalloffame.org/inductees/danny-cohen |website = [[Internet Hall of Fame]] |publisher = [[The Internet Society]] |access-date = 2015-10-07 |archive-date = 2021-07-21 |archive-url = https://web.archive.org/web/20210721114730/https://www.internethalloffame.org/inductees/danny-cohen |url-status = live }}</ref><ref>{{cite web | first = David | last = Cary | title = Endian FAQ | url = http://david.carybros.com/html/endian_faq.html | access-date = 2010-10-11 | archive-date = 2017-11-09 | archive-url = https://web.archive.org/web/20171109112101/http://david.carybros.com/html/endian_faq.html | url-status = dead }}</ref><ref>{{cite journal | last = James |first = David V. | title = Multiplexed buses: the endian wars continue | journal = [[IEEE Micro]] | date = June 1990 | volume = 10 | issue = 3 | pages = 9–21 | doi = 10.1109/40.56322 | s2cid = 24291134 | issn = 0272-1732 }}</ref><ref>{{cite web | last1 = Blanc | first1 = Bertrand | last2 = Maaraoui | first2 = Bob | title = Endianness or Where is Byte 0? | date = December 2005 | url = http://3bc.bertrand-blanc.com/endianness05.pdf | access-date = 2008-12-21 | archive-date = 2007-12-03 | archive-url = https://web.archive.org/web/20071203190220/http://3bc.bertrand-blanc.com/endianness05.pdf | url-status = live }}</ref>

Big-endianness is the dominant ordering in networking protocols, such as in the [[Internet protocol suite]], where it is referred to as ''network order'', transmitting the most significant byte first. Conversely, little-endianness is the dominant ordering for processor architectures ([[x86]], most [[ARM architecture|ARM]] implementations, base [[RISC-V]] implementations) and their associated memory. [[File format]]s can use either ordering; some formats use a mixture of both or contain an indicator of which ordering is used throughout the file.<ref>{{Cite IETF|date=April 1992|rfc=1314|title=A File Format for the Exchange of Images in the Internet|page=7|access-date=2021-08-16 }}</ref>