In computing, a hextet, or a chomp, is a sixteen-bit aggregation, or four nibbles. As a nibble typically is 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.
Bob Bemer suggested the use of hextet for 16-bit groups in 2000. In 2011 an Internet Draft explored various alternatives for hextet such as quibble, short for "quad nibble". In response to this draft, author Trefor Davies suggested the use of the word chomp because it is in line with the current denominations bit, nibble, byte.
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.
Although the word hextet is not officially recognized in the IETF documents, the word is used in technical literature on IPv6 published after the Internet Draft. Official IETF documents simply refer to them as pieces.
Cisco sources generally use the term quartet as does IPv6.com, 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.
- Bemer, Robert William (2000-08-08). "Why is a byte 8 bits? Or is it?". Computer History Vignettes. Archived from the original on 2017-04-03. Retrieved 2017-04-03.
[…] 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. […] 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 […]. 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). […] 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 […] 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". […] 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". […]
- Donnerhacke, Lutz; Hartmann, Richard; Horn, Michael; Rechthien, Kay; Weber, Leon (2011-04-07). "draft-denog-v6ops-addresspartnaming-04 - Naming IPv6 address parts". Internet Draft. 04. Archived from the original on 2017-04-03. Retrieved 2017-04-03.
- Davies, Trefor. "Bit Nibble Byte Chomp – a call to action".
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.
- IEEE Std 1754-1994 - IEEE Standard for a 32-bit Microcontroller Architecture. The Institute of Electrical and Electronics Engineers, Inc. 1994. pp. 5–7. doi:10.1109/IEEESTD.1995.79519. ISBN 978-1-55937-428-6. Retrieved 2016-02-10. (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.)
- Graziani, Rick (2012). IPv6 Fundamentals: A Straightforward Approach to Understanding IPv6. Cisco Press. p. 55. ISBN 978-0-13-303347-2.
- Coffeen, Tom (2014). IPv6 Address Planning: Designing an Address Plan for the Future. O'Reilly Media. p. 170. ISBN 978-1-4919-0326-1.
- Hinden, Robert M.; Deering, Stephen E. (December 1995). "IP Version 6 Addressing Architecture". RFC 1884. Archived from the original on 2017-04-03. Retrieved 2017-04-03.
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
- Das, Kaushik. "IPv6 Addressing".
IPv6 addresses are denoted by eight groups of hexadecimal quartets separated by colons in between them.
- Brewster, Ronald L. (1994). Data Communications and Networks, Vol. III. IEE telecommunications series. Vol. 31. Institution of Electrical Engineers. p. 155. ISBN 9780852968048. Retrieved 2017-04-03.
A data symbol represents one quartet (4 bits) of binary data.
- Courbis, Paul; Lalande, Sébastien (2006-06-27) . Voyage au centre de la HP28c/s (in French) (2 ed.). Paris, France: Editions de la Règle à Calcul. OCLC 636072913. Archived from the original on 2016-08-06. Retrieved 2015-09-06.