Giga-

:"For other meanings, see Giga (disambiguation)"

Giga- (symbol: G) is a prefix in the SI system of units denoting 10⁹, or 1,000,000,000. 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 ".

When referring to computing information units, such as gigabit or gigabyte, "giga-" can sometimes mean 1,073,741,824 (2³⁰), (Though such use is [http://physics.nist.gov/cuu/pdf/sp811.pdf 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 usually pronEng|g (with a hard "g" as in "giggle") but is sometimes pronounced IPA|/dʒ/ (with a soft "g" as in "giant").

This latter pronunciation was formalized within the United States in the 1960s and 1980s with the issue by the US National Bureau of Standards of pronunciation guides for the metric prefixes. [NBS Special Publication 304 & 304A, revised August 1981, "A Brief History of Measurement Systems"] A prominent example is found in the pronunciation of "gigawatts" in the 1985 movie "Back to the Future".

According to the American writer Kevin Self, a German committee member of the International Electrotechnical Commission proposed "giga-" as a prefix for 10⁹ in the 1920s, drawing on a verse by the humorous poet Christian Morgenstern that appeared in the third (1908) edition of "Galgenlieder" (Gallows Songs). This suggests that a hard German IPA| [g] was originally intended as the pronunciation. Self was unable to ascertain at what point the alternative pronunciation came into occasional use, but as of 1995 it had died out. [Kevin Self, April 1995, "Technically speaking", "Spectrum"]

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 abbreviated Gyr, but the preferred usage is Ga)

ee also

*SI prefix
*Binary prefix
*Gibibyte
*Gigabit Ethernet

Notes and references

External links

* [http://www.bipm.org BIPM website]