giga-: Definition from Answers.com

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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 'giant'.

When referring to computing information units, such as gigabit or gigabyte, giga can sometimes mean 1,073,741,824 (2³⁰), though such use has been discouraged by various standards organizations.^[1]^[2]. The binary prefix gibi has been suggested for 2³⁰, while reserving giga exclusively for 10⁹. See binary prefix.

1 Pronunciation
2 Common usage
3 See also
4 Notes and references
5 External links

Pronunciation

In English the initial g of giga is often pronounced /ɡ/ (a hard g as in giggle), but may also be pronounced /dʒ/ (a soft g as in its Greek root's meaning, giant).^[3]

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.^[4] 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 [ɡ] 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.^[5]

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) years. (sometimes abbreviated Gyr, but the preferred usage is Ga)

SI prefixes
1000^m	10ⁿ	Prefix	Symbol	Since^[1]	Short scale	Long scale	Decimal
1000⁸	10²⁴	yotta	Y	1991	Septillion	Quadrillion	1000000000000000000000000
1000⁷	10²¹	zetta	Z	1991	Sextillion	Trilliard	1000000000000000000000
1000⁶	10¹⁸	exa	E	1975	Quintillion	Trillion	1000000000000000000
1000⁵	10¹⁵	peta	P	1975	Quadrillion	Billiard	1000000000000000
1000⁴	10¹²	tera	T	1960	Trillion	Billion	1000000000000
1000³	10⁹	giga	G	1960	Billion	Milliard	1000000000
1000²	10⁶	mega	M	1960	Million		1 000 000
1000¹	10³	kilo	k	1795	Thousand		1000
1000^²⁄₃	10²	hecto	h	1795	Hundred		100
1000^¹⁄₃	10¹	deca	da	1795	Ten		10
1000⁰	10⁰	(none)	(none)	NA	One		1
1000^−¹⁄₃	10⁻¹	deci	d	1795	Tenth		0.1
1000^−²⁄₃	10⁻²	centi	c	1795	Hundredth		0.01
1000⁻¹	10⁻³	milli	m	1795	Thousandth		0.001
1000⁻²	10⁻⁶	micro	µ	1960^[2]	Millionth		0.000001
1000⁻³	10⁻⁹	nano	n	1960	Billionth	Milliardth	0.000000001
1000⁻⁴	10⁻¹²	pico	p	1960	Trillionth	Billionth	0.000000000001
1000⁻⁵	10⁻¹⁵	femto	f	1964	Quadrillionth	Billiardth	0.000000000000001
1000⁻⁶	10⁻¹⁸	atto	a	1964	Quintillionth	Trillionth	0.000000000000000001
1000⁻⁷	10⁻²¹	zepto	z	1991	Sextillionth	Trilliardth	0.000000000000000000001
1000⁻⁸	10⁻²⁴	yocto	y	1991	Septillionth	Quadrillionth	0.000000000000000000000001
The metric system was introduced in 1795 with six prefixes. The other dates relate to recognition by a resolution of the CGPM. The 1948 recognition of the micron by the CGPM was abrogated in 1967.

Notes and references

^ "§3.1 SI prefixes" (in French/English) (PDF). The International System of Units (SI) (8th edition ed.). Paris: STEDI Media. 2006. pp. 127. ISBN 92-822-2213-6. http://www1.bipm.org/utils/common/pdf/si_brochure_8.pdf. Retrieved 2007-02-25. "[Side note:] These SI prefixes refer strictly to powers of 10. They should not be used to indicate powers of 2 (for example, one kilobit represents 1000 bits and not 1024 bits). The IEC has adopted prefixes for binary powers in the international standard IEC 60027-2: 2005, third edition, Letter symbols to be used in electrical technology — Part 2: Telecommunications and electronics. The names and symbols for the prefixes corresponding to 2¹⁰, 2²⁰, 2³⁰, 2⁴⁰, 2⁵⁰, and 2⁶⁰ are, respectively: kibi, Ki; mebi, Mi; gibi, Gi; tebi, Ti; pebi, Pi; and exbi, Ei. Thus, for example, one kibibyte would be written: 1 KiB = 2¹⁰ B = 1024 B, where B denotes a byte. Although these prefixes are not part of the SI, they should be used in the field of information technology to avoid the incorrect usage of the SI prefixes."
^ NIST Guide for the Use of the International System of Units (Appendix D. ref 5)
^ A Practical Guide to the International System of Units, U.S. Metric Association, Feb 2008
^ NBS Special Publication 304 & 304A, revised August 1981, "A Brief History of Measurement Systems"
^ Kevin Self, April 1995, "Technically speaking", Spectrum

External links

BIPM website

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	GeV (abbreviation)
	gig-
	G

giga-

Contents

Pronunciation

Common usage

See also

Notes and references

External links