Gigabyte

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This article is about the unit of measurement. For the computer hardware manufacturer, see Gigabyte Technology.

Template:Quantities of bytes A gigabyte (derived from the SI prefix giga-) is a unit of information or computer storage equal to one billion bytes. It is commonly abbreviated GB in writing (not to be confused with Gb, which is used for gigabit) and gig in writing or speech.

There are two slightly different definitions of the size of a gigabyte in use:

1,000,000,000 bytes or 10⁹ bytes is the decimal definition used in telecommunications (such as network speeds) and some computer storage manufacturers (such as hard disks and flash drives). This usage is compatible with SI.
1,073,741,824 bytes, equal to 1024³, or 2³⁰ bytes. This is the definition used for computer memory sizes, and most often used in computer engineering, computer science, and most aspects of computer operating systems. The IEC recommends that this unit should instead be called a gibibyte (abbreviated GiB), as it conflicts with SI units used for bus speeds and the like.

1 Distinction between 1000 and 1024 megabytes
2 Gigabytes in use
3 See also
4 External links

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Distinction between 1000 and 1024 megabytes

Main article: Binary prefix

As a result of this confusion, the unadorned term gigabyte is useful only where just one digit of precision is required. In technical specifications, the first usage is typically expanded to remove the ambiguity ("GB is one billion bytes"). The only exception is RAM, where sizes are always given in the power-of-two units natural to this domain.

Thus, to convert metric gigabytes into binary gigabytes (for example a 100 GB drive contains 93 GiB when installed), follow this formula:

where <math>y</math> is size of drive in metric gigabytes

To clarify the distinction between decimal and binary prefixes, in 1997 the International Electrotechnical Commission (IEC), a standards body, proposed complete conformity with the International System of Units (SI) conventions (standard IEC 60027-2). New units were formed as unions of the SI prefixes with the word "binary". Thus 2³⁰ bytes would be called a gibibyte (GiB) while the use of gigabyte is deprecated in this context. Thus, gigabyte unambiguously follows the SI convention as 10⁹ bytes. This naming convention is steadily gaining acceptance, but deprecated usage is common. The convention must be inferred from context or fine print.

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Gigabytes in use

As of 2005, 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 hard disk manufacturers' definition of GB is 1,000,000,000 bytes (only computer memory has a natural inclination towards units that are powers of 2), most computer operating systems use the 1,073,741,824 byte definition. This distinction can cause confusion.
As of 2005, consumer hard drive per-gigabyte costs are 0.50-0.80 USD.
In speech, gigabyte is often informally abbreviated to gig, as in "This is a ten-gig hard drive".
A DVD-5 format disc is capable of storing 4.7 GB. One gigabyte is roughly equal to 18 hours of MP3 music (at 128 kbit/s).
Most USB flash drives have a capacity measured in MB but GB capacity flash drives have been released recently.