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For the Baroque dance, see gigue.

giga- (symbol: G) is a prefix in the SI system of units denoting 10⁹, or 1,000,000,000 (1 billion). The Oxford English Dictionary reports the earliest use of giga- in this sense to be "1947 Compt. Rend. de la 14me Conf. (Internat. Union of Chem.) 115 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), but can also denote 1,000,000,000 (10⁹). The exact definition being used is ambiguous, and must be determined 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.

Contents 1 Pronunciation 2 Common usage 3 See also 4 External links

In English the initial G of giga can be pronounced with a soft G (as in gigantic) or with a hard G (as in giggle). The latter hard G pronunciation has become more common, especially when referring to computer measurements such as gigabyte and gigahertz. A prominent example of the soft G pronunciation is found in the 1985 movie Back to the Future, where gigawatts was pronounced as jigawatts.

• 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 = 1,000,000,000 bit/s
• gigayear or giga-annum — one billion (10⁹) complete Julian rotation periods of the Earth about the Sun. (common abbr. Gyr)

SI prefixes

1000n	10n	Prefix	Symbol	Short scale	Long scale	Decimal equivalent in SI writing style
10008	1024	yotta	Y	Septillion	Quadrillion	1 000 000 000 000 000 000 000 000
10007	1021	zetta	Z	Sextillion	Trilliard (thousand trillion)	1 000 000 000 000 000 000 000
10006	1018	exa	E	Quintillion	Trillion	1 000 000 000 000 000 000
10005	1015	peta	P	Quadrillion	Billiard (thousand billion)	1 000 000 000 000 000
10004	1012	tera	T	Trillion	Billion	1 000 000 000 000
10003	109	giga	G	Billion	Milliard (thousand million)	1 000 000 000
10002	106	mega	M	Million		1 000 000
10001	103	kilo	k	Thousand		1 000
10002/3	102	hecto	h	Hundred		100
10001/3	101	deca, deka	da	Ten		10
10000	100	(none)	(none)	One		1
1000−1/3	10−1	deci	d	Tenth		0.1
1000−2/3	10−2	centi	c	Hundredth		0.01
1000−1	10−3	milli	m	Thousandth		0.001
1000−2	10−6	micro	µ (u)	Millionth		0.000 001
1000−3	10−9	nano	n	Billionth	Milliardth	0.000 000 001
1000−4	10−12	pico	p	Trillionth	Billionth	0.000 000 000 001
1000−5	10−15	femto	f	Quadrillionth	Billiardth	0.000 000 000 000 001
1000−6	10−18	atto	a	Quintillionth	Trillionth	0.000 000 000 000 000 001
1000−7	10−21	zepto	z	Sextillionth	Trilliardth	0.000 000 000 000 000 000 001
1000−8	10−24	yocto	y	Septillionth	Quadrillionth	0.000 000 000 000 000 000 000 001

• SI prefix
• Binary prefix
• gibibyte
• Gigabit Ethernet

• BIPM website