Gigabyte

Key takeaways

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

Reference excerpt

The gigabyte () is a multiple of the unit byte for digital information. The prefix giga- means 109 in the International System of Units (SI). Therefore, one gigabyte is one billion bytes. The unit symbol for the gigabyte is GB. This definition is used in all contexts of science (especially data science), engineering, business, and many areas of computing, including storage capacities of hard drives, solid-state drives, and tapes, as well as data transmission speeds. The term is also used in some fields of computer science and information technology to denote 1073741824 (10243 or 230) bytes, however, particularly for sizes of RAM. Thus, some usage of gigabyte has been ambiguous. To resolve this, IEC 80000-13 states that a gigabyte (GB) is 109 bytes and specifies the term gibibyte (GiB) to denote 230 bytes. These differences are still readily seen, for example, when a 400 GB drive's capacity is displayed by Microsoft Windows as 372 GB instead of 372 GiB. Analogously, a memory module that is labeled as having the size "1GB" has one gibibyte (1GiB) of storage capacity. In response to litigation over whether the makers of electronic storage devices must conform to Microsoft Windows' use of a binary definition of "GB" instead of the metric/decimal definition, the United States District Court for the Northern District of California rejected that argument, ruling that "the U.S. Congress has deemed the decimal definition of gigabyte to be the 'preferred' one for the purposes of 'U.S. trade and commerce.'"

Definition The term gigabyte has a standard definition of 10003 bytes, as well as a discouraged meaning of 10243 bytes. The latter binary usage originated as compromise technical jargon for byte multiples that needed to be expressed in a power of 2, but lacked a convenient name. As 1024 (210) is approximately 1000 (103), roughly corresponding to SI multiples, it was used for binary multiples as well. In 1998 the International Electrotechnical Commission (IEC) published standards for binary prefixes, requiring that the gigabyte strictly denote 10003 bytes and gibibyte denote 10243 bytes. By the end of 2007, the IEC Standard had been adopted by the IEEE, EU, and NIST, and in 2009 it was incorporated in the International System of Quantities. Nevertheless, the term gigabyte continues to be widely used with the following two different meanings:

Base 10 (decimal) 1 GB = 1000000000 bytes (= 10003 B = 109 B) Based on powers of 10, this definition uses the prefix giga- as defined in the International System of Units (SI). This is the recommended definition by the International Electrotechnical Commission (IEC). This definition is used in networking contexts and most storage media, particularly hard drives, flash-based storage, and DVDs, and is also consistent with the other uses of the SI prefix in computing, such as CPU clock speeds or measures of performance. The file manager of Mac OS X version 10.6 and later versions are a notable example of this usage in software, which report files sizes in decimal units.

Base 2 (binary) 1 GiB = 1073741824 bytes (= 10243 B = 230 B). The binary definition uses powers of the base 2, as does the architectural principle of binary computers. This usage is widely promulgated by some operating systems, such as Microsoft Windows in reference to computer memory (e.g., RAM). This definition is synonymous with the unambiguous unit gibibyte.

Consumer confusion Since the first disk drive, the IBM 350, disk drive manufacturers expressed hard drive capacities using decimal prefixes. With the advent of gigabyte-range drive capacities, manufacturers labelled many consumer hard drive, solid-state drive and USB flash drive capacities in certain size classes expressed in decimal gigabytes, such as "500 GB". The exact capacity of a given drive model is usually slightly larger than the class designation. Practically all manufacturers of hard disk drives and flash-memory disk devices continue to define one gigabyte as 1000000000bytes, which is displayed on the packaging. Some operating systems such as Mac OS X, iOS, Android, Ubuntu, and Debian express hard drive capacity or file size using decimal multipliers, while others such as Microsoft Windows (including Windows Phone) report file size using binary multipliers. This discrepancy causes confusion, as a disk with an advertised capacity of, for example, 400 GB (meaning 400000000000bytes, equal to 372 GiB) might be reported by the operating system as "372 GB". For RAM, the JEDEC memory standards use IEEE 100 nomenclature which quote the gigabyte as 1073741824bytes (230 bytes). The difference between units based on decimal and binary prefixes increases as a semi-logarithmic (linear-log) function—for example, the decimal kilobyte value is nearly 98% of the kibibyte, a megabyte is under 96% of a mebibyte, and a gigabyte is just over 93% of a gibibyte value. This means that a 300 GB (279 GiB) hard disk might be indicated variously as "300 GB", "279 GB" or "279 GiB", depending on the operating system. As storage sizes increase and larger units are used, these differences become more pronounced: a 30,000 GB (27,940 GiB) heat-assisted magnetic recording hard drive might be reported by an operating system using binary units as having a capacity of only 27,490 GB, creating an apparent shortfall of over 2 terabytes.

US lawsuits Early lawsuits disputing manufacturers' use of "gigabyte" to mean 109 bytes ended in settlement with no court ruling on the question, such as a lawsuit against drive manufacturer Western Digital. Western Digital settled the challenge and added explicit disclaimers to products that the usable capacity may differ from the advertised capacity. Seagate was sued on similar grounds and also settled. A later lawsuit, decided in 2019, arose from an alleged breach of contract and other claims over the binary and decimal definitions used for "gigabyte". This lawsuit ended in favour of the manufacturers, with courts holding that the legal definition of gigabyte or GB is 1 GB = 1,000,000,000 (109) bytes (the decimal definition). Specifically, the courts held that "the U.S. Congress has deemed the decimal definition of gigabyte to be the 'preferred' one for the purposes of 'U.S. trade and commerce'. ... The California Legislature has likewise adopted the decimal system for all 'transactions in this state'."

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Illustrations

Worked examples

Example 1 — a first encounter with Gigabyte

Start with the simplest possible case. Write down what Gigabyte claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In 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 Gigabyte 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 Gigabyte 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 Gigabyte

In research: Gigabyte appears in 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 Gigabyte 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: Gigabyte 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 Gigabyte 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.

How to study Gigabyte in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Gigabyte 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 Gigabyte out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Gigabyte in simple terms?

The gigabyte () is a multiple of the unit byte for digital information. The prefix giga- means 109 in the International System of Units (SI).

Why does Gigabyte matter?

Because it connects several 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 Gigabyte?

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 Gigabyte.