computer science

Octet (computing)

Octet (computing) is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Octet (computing) rather than just read about it. In short: The octet is a unit of digital information in computing and telecommunications that consists of eight bits. The term is often used when the term byte might be ambiguous, as the term byte has historically been used for storage units of a variety of sizes.

Key takeaways

Octet (computing) belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Octet (computing) to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Octet (computing) from memory before moving on to harder problems.

Reference excerpt

The octet is a unit of digital information in computing and telecommunications that consists of eight bits. The term is often used when the term byte might be ambiguous, as the term byte has historically been used for storage units of a variety of sizes. The term octad(e) for eight bits is no longer common.

Definition The international standard IEC 60027-2, chapter 3.8.2, states that a byte is an octet of bits. However, the unit byte has historically been platform-dependent and has represented various storage sizes in the history of computing. Due to the influence of several major computer architectures and product lines, the byte became overwhelmingly associated with eight bits. This meaning of byte is codified in such standards as ISO/IEC 80000-13. While byte and octet are often used synonymously, those working with certain legacy systems are careful to avoid ambiguity. Octets can be represented using number systems of varying bases such as the hexadecimal, decimal, or octal 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) is often used when the use of byte might be ambiguous. It is frequently used in the Request for Comments (RFC) publications of the Internet Engineering Task Force to describe storage sizes of network protocol parameters. The earliest example is RFC 635 from 1974. In 2000, Bob Bemer claimed to have earlier proposed the usage of the term octet for "8-bit bytes" when he headed software operations for Cie. Bull in France in 1965 to 1966. In France, French Canada and formerly in Romania, 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, a usage no longer common. Early examples of usage exist in British, Dutch and German sources of the 1960s and 1970s, and throughout the documentation of Philips mainframe computers. 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.

Use in Internet Protocol addresses The octet is used in representations of Internet Protocol computer network addresses. 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 dot (a full stop/period). 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.

Worked examples

Example 1 — a first encounter with Octet (computing)

Start with the simplest possible case. Write down what Octet (computing) claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Octet (computing) before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Octet (computing) ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Octet (computing)

In research: Octet (computing) appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Octet (computing) in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Octet (computing) is common in secondary-school and first-year university syllabi. It links to neighbouring topics Units of information, so understanding it makes those chapters shorter.
In everyday life: Look for Octet (computing) outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Octet (computing) in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Octet (computing) means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Octet (computing) out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Octet (computing) in simple terms?

Why does Octet (computing) matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Octet (computing)?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Octet (computing).