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Template:Two other uses A gigabyte or Gbyte (derived from the SI prefix giga-) is a unit of information or computer storage meaning either 1000³ bytes or 1024³ bytes (1000³ = one billion). 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. However, since there are no other uses for the term 'Gigabyte' apart from refering to memory, file sizes, storage capacity, amounts of network traffic, the standards bodies' recommendations are frequently ignored amongst so-called computer professionals, and 'Gigabyte' is used by them as if it were 1024³ bytes.

It is commonly abbreviated GB (not to be confused with Gb, which is used for gigabits).

Definition

There are two different definitions of gigabyte in general use:

• 1,000,000,000 bytes or 10 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", and, "One gigabyte, or GB, equals one billion bytes when referring to hard drive capacity". Similar quotes are found on the websites of other storage manufacturers.
• 1,073,741,824 bytes, equal to 1024³, or 2 bytes. This is the definition commonly used for computer memory and file sizes. Microsoft uses this definition to display hard drive sizes, as do most other operating systems . Every operating system uses this definition when referring to the size of files by default. By this definition, there are 1,024 megabytes in a gigabyte. Since 1999, the IEC recommends that this unit should instead be called a gibibyte (abbreviated GiB).

Gigabytes vs. gigabits

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

In computer networking, however, the conventional SI units are followed. Manufacturers of networking equipment always use 1000-bit kilobits as their basic unit of measurement.

	Abbreviation	No. of bytes	Usage
gigabytes	GB (Note: uppercase "B")	1000	Computer storage (eg 500 GB hard disk)
gigabytes	GB (Note: uppercase "B")	1024	Computer memory (eg 4 GB RAM)
gigabit	Gb (Note: lowercase "b")	${\displaystyle 125*1000^{2}}$	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 400 gigabytes may have its capacity reported by the operating system as only 372 GB, depending on the type of report.

The difference between units based on 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 = 3×2 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.

A an example, take a hard drive that can store exactly 250×10 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.

To further complicate matters, flash memory chips are organized in multiples of 2, but retail flash memory products have available capacities specified by multiples of 10. Removable flash storage products contain file systems that make the devices behave like hard disks instead of RAM, yet it is called 'memory'. In operating systems like Windows Vista, flash memory can indeed be treated like RAM.

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. However, JEDEC memory standards still uses the IEEE 100 nomanclatures.

Gigabytes in use

This article contains a list of miscellaneous information. Please relocate any relevant information into other sections or articles. (October 2007)

• The human genome contains 0.791175 GB of data (the 3.1647×10 base pairs represented as 2-bits).
• A DVD-5 format disc is specified as capable of storing 4.7 gigabytes (4,700,000,000 bytes), or roughly 4.38 gibibytes. A DVD-9 is capable of storing 8.5 gigabytes, or roughly 7.91 gibibytes.
• One gigabyte can hold over 1000 novels (uncompressed at 100,000 words per novel).
• One gigabyte is roughly equal to 18 hours of MP3 music at 128 kbit/s (1,024 / 128 / 1000 * 8 / 3600 = 18.64).
• One gigabyte is roughly equivalent to 12 hours of Flash Video (at 450x370).
• Most 6th generation and all 7th generation game consoles have game discs that are around 1 GB or more: PlayStation (CD-ROM - 0.7 GB), 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 Disc - 50 GB).
• Dual-layer Blu-ray Discs and dual-layer HD DVD discs can hold about 50 gigabytes (50,000,000,000 bytes) and 30 gigabytes (30,000,000,000 bytes) of data, respectively.

See also

• Gibibyte
• Gigabit
• Megabyte
• Terabyte
• Binary prefix
• JEDEC memory standards
• Orders of magnitude (data)

References

3. HP Notebook PCs - Size of Disk Drive Does not Match Specifications (Windows XP)

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

• Articles with trivia sections from October 2007
• Units of information