For other meanings, see Giga (disambiguation)

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Giga- (symbol: G) is a prefix in the SI system of units denoting 10⁹, or 1,000,000,000 (1 thousand million). The Oxford English Dictionary reports the earliest written use of giga- in this sense to be in the Reports of the IUPAC 14th Conference in 1947: "The following prefixes to abbreviations for the names of units should be used: G giga- 10⁹×". Giga- comes from the Greek γίγας, meaning 'giant'.

When referring to computing information units, such as gigabit or gigabyte, giga- can sometimes mean 1,073,741,824 (2³⁰), (Though such use is incorrect) and is better used only to denote strictly 1,000,000,000 (10⁹). Any ambiguity is best resolved from context. The binary prefix gibi- has been standardized for 2³⁰, while reserving giga- exclusively for 10⁹, to resolve this ambiguity, but has yet to achieve widespread usage. See binary prefix.

Pronunciation

In English the initial g of giga is properly pronounced with a hard g (as in giggle) but is sometimes pronounced with a soft g (as in giant). According to the American writer Self, in the 1920s a German committee member of the International Electrotechnical Commission proposed giga- as a prefix for 10⁹, drawing on a verse by the humorous poet Christian Morgenstern that appeared in the third (1908) edition of Galgenlieder (Gallows Songs). This suggests a hard German g was originally intended as the pronunciation. Self was unable to ascertain at what point the soft g pronunciation came into occasional use, but as of 1995 current practice had returned to hard g.^[1] A prominent example of the soft G pronunciation is found in the 1985 movie Back to the Future, where gigawatts was pronounced as jigawatts.

In the United States, it is well documented that the National Bureau of Standards issued pronunciation guides for the metric prefixes in the 1960s and again as late as the 1980s, giving the 'g' in "giga" a soft "j" sound, thus formalizing the pronunciation as "jiga"^[2] within the United States.

Common usage

• gigabyte — for instance, in hard disk capacity, 120 GB = 120,000,000,000 bytes; in file sizes, 1 GB = 1,073,741,824 bytes (also termed a gibibyte to reduce ambiguity)
• gigahertz — clock rate of a CPU, for instance, 3 GHz = 3,000,000,000 Hz
• gigabit — bandwidth of a network, for instance, 1 Gbit/s = 1,000,000,000 bit/s
• gigayear or gigaannum — one billion (10⁹) complete Julian rotation periods of the Earth about the Sun. (sometimes abbr. Gyr, but the preferred usage is Ga)

See also

• SI prefix
• Binary prefix
• gibibyte
• Gigabit Ethernet

Notes and references

External links

• BIPM website