Discover

A 'gigabyte' or Gbyte (derived from the SI prefix ''giga-'') is a unit of information or computer storage equal to 1000³ bytes or 1024³ bytes (1000³ = one billion). It is commonly abbreviated 'GB' (not to be confused with 'Gb', which is used for gigabits).
The usage of the word "gigabyte" is ambiguous, depending on the context. When referring to RAM sizes and file sizes, it traditionally has a binary definition, of 1024³ bytes. For every other use, it means exactly 1000³ bytes. In order to address this confusion, currently all relevant standards bodies promote the use of the term "gibibyte" for the binary definition.

Contents

Definition

Gigabytes vs gigabits

Consumer confusion

Gigabytes in use

See also

References

External links

Definition

There are two slightly different definitions of gigabyte in general use:

★ 1,000,000,000 bytes or 10⁹ bytes is the decimal definition used in telecommunications (such as network speeds) and most computer storage manufacturers (such as hard disks and flash drives). This usage is compatible with SI. Quotes from Seagate: "The storage industry standard is to display capacity in decimal",^[1] and, "One gigabyte, or GB, equals one billion bytes when referring to hard drive capacity".^[2] Similar quotes are found on the websites of other storage manufacturers.

★ 1,073,741,824 bytes, equal to 1024³, or 2³⁰ bytes. This is the definition commonly used for computer memory and file sizes. Since 1999, the IEC recommends that this unit should instead be called a gibibyte (abbreviated 'GiB'). Microsoft uses this definition to display hard drive size, as do most other operating systems ^[3]. Every operating system uses this definition when referring to the size of files.

Gigabytes vs gigabits

In conventional modern usage, a byte is 8 bits. One gigabyte is equivalent to eight gigabits.

	Abbreviation	No. of megabytes	Usage
gigabytes	GB (Note: uppercase "B")	1000	Computer storage (eg 500 GB hard disk)
gigabytes	GB (Note: uppercase "B")	1024	Computer storage (eg 4 GB RAM)
gigabit	Gb (Note: lowercase "b")	125	Network throughput (eg 1 Gb/s data transfer rate)

Consumer confusion

As of 2007, most consumer hard drives are defined by their gigabyte-range capacities. The true capacity is usually some number above or below the class designation. Although most manufacturers of hard disks and Flash disks define 1 gigabyte as 1,000,000,000 bytes, the computer operating systems used by most users usually calculate a gigabyte by dividing the bytes (whether it is disk capacity, file size, or system RAM) by 1,073,741,824. This distinction is a cause of confusion, especially for people from a non-technical background, as a hard disk with a manufacturer rated capacity of 40 gigabytes may have its capacity reported by the operating system as only 37.2 GB, depending on the type of report.
The difference between SI and binary prefixes increases exponentially — in other words, an SI kilobyte is nearly 98% as much as a kibibyte, but a megabyte is under 96% as much as a mebibyte, and a gigabyte is just over 93% as much as a gibibyte. This means that a 500 GB hard disk drive would appear as "465 GB". As storage sizes get larger and higher units are used, this difference will become more pronounced.
Note that computer memory is addressed in base 2, due to its design, so memory size is always a power of two (or some closely related quantity, for instance 384 MiB = 3×2²⁷ bytes). It is thus convenient to work in binary units for RAM. Other computer measurements, like storage hardware size, data transfer rates, clock speeds, operations per second, etc., do not have an inherent base, and are usually presented in decimal units.
As an example, take a hard drive that can store exactly 250 or 250 billion bytes after formatting. Generally, operating systems calculate disk and file sizes using ''binary'' numbers, so this 250 GB drive would be reported as "232.83 GB". The result is that there is a significant discrepancy between what the consumer believes they have purchased and what their operating system says they have.
Some consumers feel short-changed when they discover the difference, and claim that manufacturers of drives and data transfer devices are using the decimal measurements in an intentionally misleading way to inflate their numbers. Several legal disputes have been waged over the confusion. ''See Binary prefix — Legal disputes.''
The basis of the problem is of course that the official definition of the SI units is not well known, and some legal settlements include directions for manufacturers to use clearer info, e.g. by stating a hard disk's size in both GB and GiB.

Gigabytes in use

★ The human genome contains 0.791175 GB of data (the 3.1647 base pairs[3] represented as 2-bits).

★ A DVD-5 format disc is specified as capable of storing 4.7 gigabytes (4700000000 bytes), or roughly 4.38 gibibytes. A DVD-9 is capable of storing 8.5 gigabytes, or roughly 7.91 gibibytes.

★ One gigabyte is roughly equal to 18 hours of MP3 music (at 128 kbit/s).

★ One gigabyte is roughly equivalent to 11 hours, 40 minutes of Flash video (at 450x370).

★ Most 6th generation and all 7th generation game consoles have game discs that are around 1 GB or more: Dreamcast (GD-ROM - 1.2 GB), Nintendo GameCube (MiniDVD - 1.5 GB), PlayStation 2, Xbox, Xbox 360, and Wii (DVD - 8.5 GB), and PlayStation 3 (Blu-ray - 50 GB).

★ Dual-layer Blu-ray Discs and dual-layer HD DVD discs can hold about 50 gigabytes and 30 gigabytes of data, respectively.

See also

★ Gibibyte

★ Gigabit

★ Binary prefix

★ JEDEC memory standards

★ Orders of magnitude (data)

References

External links

★ http://physics.nist.gov/cuu/Units/binary.html

★ http://www.iec.ch/zone/si/si_bytes.htm

★ http://www.quinion.com/words/turnsofphrase/tp-kib1.htm

★ http://www.nist.gov/public_affairs/techbeat/tb9903.htm