Octet (computing)

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octet
Unit system
units derived from bit
Unit ofdigital information, data size
Symbolo
In primary units of information1 o = 8 bits

The octet is a

telecommunications that consists of eight bits. The term is often used when the term byte
might be ambiguous, as the byte has historically been used for storage units of a variety of sizes.

The term octad(e) for eight bits is no longer common.[1][2]

Definition

The international standard

ISO/IEC 80000-13. While byte and octet are often used synonymously, those working with certain legacy systems are careful to avoid ambiguity.[citation needed
]

Octets can be represented using number systems of varying bases such as the

number systems
. The binary value of all eight bits set (or activated) is 111111112, equal to the hexadecimal value FF16, the decimal value 25510, and the octal value 3778. One octet can be used to represent decimal values ranging from 0 to 255.

The term octet (symbol: o

Cie. Bull in France in 1965 to 1966.[3]

In

, octet is used in common language instead of byte when the eight-bit sense is required; for example, a megabyte (MB) is termed a megaoctet (Mo).

A variable-length sequence of octets, as in

Abstract Syntax Notation One
(ASN.1), is referred to as an octet string.

Octad

Historically, in Western Europe, the term octad (or octade) was used to specifically denote eight bits,[2][1] a usage no longer common. Early examples of usage exist in British,[2] Dutch and German sources of the 1960s and 1970s, and throughout the documentation of Philips mainframe computers.[1] Similar terms are triad for a grouping of three bits and decade for ten bits.

Unit multiples

Unit multiples of the octet may be formed with

SI prefixes and binary prefixes (power of 2 prefixes) as standardized by the International Electrotechnical Commission
in 1998.

SI prefixes
kilooctet (ko) = 103 octets = 1000 octets
megaoctet (Mo) = 106 octets = 1000 ko = 1000000 octets
gigaoctet (Go) = 109 octets = 1000 Mo = 1000000000 octets
teraoctet (To) = 1012 octets = 1000 Go = 1000000000000 octets
petaoctet (Po) = 1015 octets = 1000 To = 1000000000000000 octets
exaoctet (Eo) = 1018 octets = 1000 Po = 1000000000000000000 octets
zettaoctet (Zo) = 1021 octets = 1000 Eo = 1000000000000000000000 octets
yottaoctet (Yo) = 1024 octets = 1000 Zo = 1000000000000000000000000 octets
Binary prefixes
kibioctet (Kio, also written Ko, as distinct from ko) = 210 octets = 1024 octets
mebioctet (Mio) = 220 octets = 1024 Kio = 1048576 octets
gibioctet (Gio) = 230 octets = 1024 Mio = 1073741824 octets
tebioctet (Tio) = 240 octets = 1024 Gio = 1099511627776 octets
pebioctet (Pio) = 250 octets = 1024 Tio = 1125899906842624 octets
exbioctet (Eio) = 260 octets = 1024 Pio = 1152921504606846976 octets
zebioctet (Zio) = 270 octets = 1024 Eio = 1180591620717411303424 octets
yobioctet (Yio) = 280 octets = 1024 Zio = 1208925819614629174706176 octets

Use in Internet Protocol addresses

The octet is used in representations of Internet Protocol computer network addresses.[4] An

IPv4
address consists of four octets, usually displayed individually as a series of decimal values ranging from 0 to 255, each separated by a full stop (dot). Using octets with all eight bits set, the representation of the highest-numbered IPv4 address is 255.255.255.255.

An IPv6 address consists of sixteen octets, displayed in hexadecimal representation (two hexits per octet), using a colon character (:) after each pair of octets (16 bits are also known as hextet) for readability, such as 2001:0db8:0000:0000:0123:4567:89ab:cdef.[5]

See also

Notes

  1. Intel convention
    .

References

External links

  • The dictionary definition of octet at Wiktionary