{{Short description|Group of 16 bits}} {{Distinguish|Hexlet (disambiguation){{!}}Hexlet}} In computing, a '''hextet''', or a ''chomp'', is a sixteen-bit aggregation,<ref name="Bemer_2000_Hextet"/><ref name="Internet_Draft_2011"/> or four nibbles. As a nibble is typically notated in hexadecimal format, a hextet consists of 4 hexadecimal digits. A hextet is the unofficial name for each of the 8 blocks in an IPv6 address.
A hextet is also referred to as a '''segment''' in some documentation.<ref>{{Cite web |title=IPv4 and IPv6 address formats |url=https://www.ibm.com/docs/en/ts3500-tape-library?topic=functionality-ipv4-ipv6-address-formats |access-date=2024-08-02 |website=www.ibm.com |language=en-us}}</ref>
==History== Bob Bemer suggested the use of hextet for 16-bit groups in 2000.<!-- possibly earlier, but the first archived snapshot of the published document dates from 2000. --><ref name="Bemer_2000_Hextet"/> In 2011 an Internet Draft explored various alternatives for hextet, such as ''quibble'', short for "quad nibble".<ref name="Internet_Draft_2011"/> In response to this draft, author Trefor Davies suggested the use of the word ''chomp'' because it is in line with the current terminology ''bit'', ''nibble'', ''byte''.<ref name="Trefor_2011"/>
''Hextet'' would more properly describe a 6-bit aggregation, whereas the exact term for 16 bits should be ''hexadectet'', directly related to the term octet (for 8 bits). However, because it is harder to pronounce, the short form ''hextet'' is used—in analogy to how ''hex'' is commonly used as an abbreviation for ''hexadecimal'' in computing. This usage of ''hex'' to mean 16 is also in line with the similar IEEE 1754 term ''hexlet'' indicating 16 octets.<ref name="IEEE1754-1994">{{Cite book |title=IEEE Std 1754-1994 - IEEE Standard for a 32-bit Microcontroller Architecture |publisher=The Institute of Electrical and Electronics Engineers, Inc. |isbn=978-1-55937-428-6 |doi=10.1109/IEEESTD.1995.79519 |pages=5–7|year=1994}} (NB. The standard defines doublets, quadlets, octlets and hexlets as 2, 4, 8 and 16 bytes, giving the numbers of bits (16, 32, 64 and 128) only as a secondary meaning.)</ref>
Although the word ''hextet'' is not officially recognized in the IETF documents, it is used in technical literature on IPv6<ref name="Graziani2012"/><ref name="Coffeen2014"/> published after the Internet Draft. Official IETF documents simply refer to them as ''pieces''.<ref name="IPv6_1995"/>
Cisco sources generally{{Citation needed|date=April 2017|reason=This article documents a Cisco Press book using "Hextet", therefore we need a source documenting the claimed "general" use of "Quartet" by Cisco.}} use the term ''quartet'' as does IPv6.com,<ref name="IPv6_Addressing"/> a reference either to the four-digit grouping or to the fact that it represents four nibbles; however, this term is also used by some to refer to a four-bit aggregation.<ref name="Brewster_1994"/><ref name="Courbis_1989"/>
==See also== *Sextet (group of 6 bits) *Doublet (2 octets)
==References== {{Reflist|refs= <ref name="Bemer_2000_Hextet">{{Cite web |title=Why is a byte 8 bits? Or is it? |author-first=Robert William |author-last=Bemer |author-link=Robert William Bemer |work=Computer History Vignettes |date=2000-08-08 |url=http://www.bobbemer.com/BYTE.HTM |access-date=2017-04-03 |url-status=dead |archive-url=https://web.archive.org/web/20170403130829/http://www.bobbemer.com/BYTE.HTM |archive-date=2017-04-03 |quote=[…] I came to work for IBM, and saw all the confusion caused by the 64-character limitation. Especially when we started to think about word processing, which would require both upper and lower case. […]<!-- Add 26 lower case letters to 47 existing, and one got 73 -- 9 more than 6 bits could represent.--> I even made a proposal (in view of STRETCH, the very first computer I know of with an 8-bit byte) that would extend the number of punch card character codes to 256 […].<!-- [1]. Some folks took it seriously. I thought of it as a spoof. --> So some folks started thinking about 7-bit characters, but this was ridiculous. With IBM's STRETCH computer as background, handling 64-character words divisible into groups of 8 (I designed the character set for it, under the guidance of Dr. Werner Buchholz, the man who DID coin the term "byte" for an 8-bit grouping). […]<!-- [2] --> It seemed reasonable to make a universal 8-bit character set, handling up to 256. In those days my mantra was "powers of 2 are magic". And so the group I headed developed and justified such a proposal […]<!-- [3]. That was a little too much progress when presented to the standards group that was to formalize ASCII, so they stopped short for the moment with a 7-bit set, or else an 8-bit set with the upper half left for future work. --> The IBM 360 used 8-bit characters, although not ASCII directly. Thus Buchholz's "byte" caught on everywhere. I myself did not like the name for many reasons. The design had 8 bits moving around in parallel. But then came a new IBM part, with 9 bits for self-checking, both inside the CPU and in the tape drives. I exposed this 9-bit byte to the press in 1973. But long before that, when I headed software operations for Cie. Bull in France in 1965-66, I insisted that "byte" be deprecated in favor of "octet". […]<!-- You can notice that my preference then is now the preferred term. --> It is justified by new communications methods that can carry 16, 32, 64, and even 128 bits in parallel. But some foolish people now refer to a "16-bit byte" because of this parallel transfer, which is visible in the UNICODE set. I'm not sure, but maybe this should be called a "hextet". […]<!-- But you will notice that I am still correct. Powers of 2 are still magic! --> }}</ref> <ref name="Internet_Draft_2011">{{Cite journal |title=draft-denog-v6ops-addresspartnaming-04 - Naming IPv6 address parts |version=04 |date=2011-04-07 |journal=Internet Draft |author-first1=Lutz |author-last1=Donnerhacke |author-first2=Richard |author-last2=Hartmann |author-first3=Michael |author-last3=Horn |author-first4=Kay |author-last4=Rechthien |author-first5=Leon |author-last5=Weber <!-- |contributor-first1=Ronny |contributor-last1=Boesger |contributor-first2=Thorsten |contributor-last2=Dahm |contributor-first3=Joerg |contributor-last3=Dorchain |contributor-first4=Sascha |contributor-last4=Lenz |contributor-first5=Jens |contributor-last5=Link |contributor-first6=Jan |contributor-last6=Walzer |contributor-first7=Sebastian |contributor-last7=Wiesinger --> |url=http://tools.ietf.org/html/draft-denog-v6ops-addresspartnaming-04 |access-date=2017-04-03 |url-status=live|archive-url=https://web.archive.org/web/20170403202622/https://tools.ietf.org/html/draft-denog-v6ops-addresspartnaming-04 |archive-date=2017-04-03}}</ref> <ref name="Graziani2012">{{Cite book |author-first=Rick |author-last=Graziani |title=IPv6 Fundamentals: A Straightforward Approach to Understanding IPv6 |year=2012 |publisher=Cisco Press |isbn=978-0-13-303347-2 |page=55 |url=https://books.google.com/books?id=FbYjJjZNA5gC&pg=PA55}}</ref> <ref name="Coffeen2014">{{Cite book |author-first=Tom |author-last=Coffeen |title=IPv6 Address Planning: Designing an Address Plan for the Future |year=2014 |publisher=O'Reilly Media |isbn=978-1-4919-0326-1 |page=170 |url=https://books.google.com/books?id=dZU8BQAAQBAJ&pg=PT170}}</ref> <ref name="IPv6_1995">{{Cite web |title=IP Version 6 Addressing Architecture |author-first1=Robert M. |author-last1=Hinden |author-first2=Stephen E. |author-last2=Deering |date=December 1995 |rfc=1884 |url=http://tools.ietf.org/html/rfc1884#page-4 |access-date=2017-04-03 |url-status=live |archive-url=https://web.archive.org/web/20170403204750/https://tools.ietf.org/html/rfc1884 |archive-date=2017-04-03 |quote=The preferred form is x:x:x:x:x:x:x:x, where the 'x's are the hexadecimal values of the eight 16-bit pieces of the address}}</ref> <ref name="IPv6_Addressing">{{Cite web |title=IPv6 Addressing |author-first=Kaushik |author-last=Das |url=http://ipv6.com/articles/general/IPv6-Addressing.htm |quote=IPv6 addresses are denoted by eight groups of hexadecimal quartets separated by colons in between them.}}</ref> <ref name="Brewster_1994">{{Cite book |title=Data Communications and Networks, Vol. III |author-first=Ronald L. |author-last=Brewster |volume=31 |series=IEE telecommunications series |publisher=Institution of Electrical Engineers |year=1994 |isbn=9780852968048 |page=155 |url=https://books.google.com/books?id=7O5EXtN94PIC&pg=PA155 |access-date=2017-04-03 |quote=A data symbol represents one quartet (4 bits) of binary data.}}</ref> <ref name="Courbis_1989">{{Cite book |title=Voyage au centre de la HP28c/s |author-first1=Paul |author-last1=Courbis |author-link1=Paul Courbis |author-first2=Sébastien |author-last2=Lalande |language=French |publisher=Editions de la Règle à Calcul |location=Paris, France |edition=2 |date=2006-06-27 |orig-year=1989 |oclc=636072913 |url=http://www.courbis.fr/spip.php?article17 |access-date=2015-09-06 |url-status=live |archive-url=https://web.archive.org/web/20160806084555/http://www.courbis.fr/Voyage-au-centre-de-la-HP28-c-s,17.html |archive-date=2016-08-06}}</ref> <ref name="Trefor_2011">{{Cite web | title=Bit Nibble Byte Chomp – a call to action |author-first=Trefor |author-last=Davies |date=22 March 2011 |url=http://www.trefor.net/2011/03/22/bit-nibble-byte-chomp-a-call-to-action/ |quote=The Timico engineering team has started to use the word “chomp” to represent two bytes or the 4 Hex character block in IPv6. Chomp is clearly in the mould of bit, nibble and byte and I would be grateful if you could chew this one over with a view to supporting the idea – we are submitting it as a suggestion when the above Draft expires.}}</ref> }}
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