Gigabyte
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- This article is about the unit of measurement, for the computer hardware manufacturer see Gigabyte Technology.
A gigabyte (symbol GB) is a unit of measurement in computers of one thousand million bytes (the same as one billion bytes in the short scale usage). However, because computers work on the binary system, rather than a gigabyte being 103 megabytes (1000 MBs), the term gigabyte correctly means 210 megabytes (1024 MiBs). In the latter case, it can be abbreviated as GiB (recommended) or GB (traditional).
Because of irregularities in using the binary prefix in the definition and usage of the kilobyte, the exact number in common practice could be either one of the following:
- 1 000 000 000 bytes or 109 bytes is the definition used by telecommunications engineers and some storage manufacturers. This is consistent with the SI prefix "giga-".
- 1 073 741 824 bytes, equal to 10243, or 230. This is the definition most often used in computer engineering, computer science, computer programming, and almost all computer operating systems. It has been suggested that this measure can be abbreviated as GiB (gibibyte) to avoid ambiguity, as defined in IEC 60027-2 but is seldomly done.
See integral data type.
Likewise, a terabyte is either equal to 1024 gigabytes or to 1000 gigabytes depending on the usages.
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 100GB drive contains 93GiB when installed), follow this formula:
- <math>\frac{y \cdot 10^9}{2^{30}}<math>
where <math>y<math> is size of drive in metric gigabytes
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Gigabytes in use
As of 2005, most consumer hard drives are measured in gigabyte-range capacities. Per-gigabyte costs are 0.50-0.80 USD.
In speech, gigabyte is often abbreviated to gig, as in "This is a ten-gig hard drive". The initial G in giga- is usually pronounced hard as in geek, not soft as in giant, however both pronounciations are equally valid.
A gigabit, which should not be confused with gigabyte, is 1/8th of a gigabyte and is mainly used to describe bandwidth, e.g. 2 gigabit/s is the speed of current Fibre Channel interfaces.
Unicode has a symbol for Gigabyte: (㎇).
Distinction between 1000 and 1024 megabytes
- Main article: Binary prefix
To clarify the distinction between decimal and binary prefixes, the International Electrotechnical Commission (IEC), a standards body, in 1997 proposed short unions of the International System of Units (SI) prefixes with the word "binary". Thus meaning (2) would be called a gibibyte (GiB). This naming convention has not yet been widely accepted.
Origin of prefix
The prefix "giga" comes from the Greek word γίγας (gigas) meaning "giant", and was chosen because 109 can be described as a "gigantic" number.
See also
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
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