Giga-

For other uses, see Giga (disambiguation).

Giga- (/ˈɡɪɡə/ or /ˈdʒɪɡə/) is a unit prefix in the metric system denoting a factor of a short-scale billion or long-scale milliard (10⁹ or 1,000,000,000). It has the symbol G.

Laptop hard drive, with its platter exposed.

Giga- is derived from the Greek word γίγας (gígas), meaning "giant". The Oxford English Dictionary reports the earliest written use of giga in this sense to be in the Reports of the IUPAC 14th Conférence Internationale de Chimie in 1947: "The following prefixes to abbreviations for the names of units should be used: G giga 10⁹×."^[1] However, it was already used in 1932 by the German organization Verband deutscher Elektrotechniker.^[2]

When referring to information units in computing, such as gigabyte, giga may sometimes mean 1073741824 (2³⁰); this causes ambiguity. Standards organizations discourage this and use giga- to refer to 10⁹ in this context too.^{[3][4][non-primary source needed]} Gigabit is only rarely used with the binary interpretation of the prefix. The binary prefix gibi has been adopted for 2³⁰, while reserving giga exclusively for the metric definition.

Pronunciation

In English, the prefix giga can be pronounced /ˈɡɪɡə/ (a hard g as in giggle), or /ˈdʒɪɡə/ (a soft g as in gigantic, which shares giga's Ancient Greek root).^[5] A prominent example of this latter pronunciation is found in the pronunciation of gigawatts in the 1985 film 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 (evidently "Anto-logie") by the German humorous poet Christian Morgenstern that appeared in the third (1908) edition of his Galgenlieder (Gallows Songs).^[6][7] This suggests that a hard German [ɡ] was originally intended as the pronunciation. Self was unable to ascertain when the /dʒ/ (soft g) pronunciation came into occasional use, but claimed that as of 1995 it had returned to /ɡ/ (hard g).^[8][9]

In 1998, a poll by the phonetician John C. Wells found that 84% of Britons preferred the pronunciation of gigabyte starting with /ɡɪ/ (as in gig), 9% with /dʒɪ/ (as in jig), 6% with /ɡaɪ/ (guy), and 1% with /dʒaɪ/ (as in giant).^[10]

Common usage

• gigahertz—clock rate of a CPU, for instance, 3 GHz = 3000000000Hz
• gigabit—bandwidth of a network link, for instance, 1 Gbit/s = 1000000000bit/s.
• gigabyte—for instance, for hard disk capacity, 120 GB = 120000000000bytes;
• gigayear or gigaannum—one billion (10⁹) years, sometimes abbreviated Gyr, but the preferred usage is Ga or, for years ago, GA.^[11]

SI prefixes

• v
• t
• e

Prefix		Base 10	Decimal	Adoption [nb 1]
Name	Symbol
quetta	Q	1030	1000000000000000000000000000000	2022[12]
ronna	R	1027	1000000000000000000000000000
yotta	Y	1024	1000000000000000000000000	1991
zetta	Z	1021	1000000000000000000000
exa	E	1018	1000000000000000000	1975[13]
peta	P	1015	1000000000000000
tera	T	1012	1000000000000	1960
giga	G	109	1000000000
mega	M	106	1000000	1873
kilo	k	103	1000	1795
hecto	h	102	100
deca	da	101	10
—	—	100	1	—
deci	d	10−1	0.1	1795
centi	c	10−2	0.01
milli	m	10−3	0.001
micro	μ	10−6	0.000001	1873
nano	n	10−9	0.000000001	1960
pico	p	10−12	0.000000000001
femto	f	10−15	0.000000000000001	1964
atto	a	10−18	0.000000000000000001
zepto	z	10−21	0.000000000000000000001	1991
yocto	y	10−24	0.000000000000000000000001
ronto	r	10−27	0.000000000000000000000000001	2022[12]
quecto	q	10−30	0.000000000000000000000000000001
Notes Prefixes adopted before 1960 already existed before SI. The introduction of the centimetre–gram–second system of units was in 1873.

Binary prefix

The notation 1 GB represents 1,000,000,000 bytes or, in deprecated usage, 1,073,741,824 (2³⁰) bytes. Per IEC 60027-2 A.2 and ISO/IEC 80000 standards, the correct notation of 2³⁰ is gibi (symbol Gi).^[14] One gibibyte (1 GiB) is 1,073,741,824 bytes or 1.074 GB. Despite international standards, the use of 1 GB = 2³⁰ B is widespread. A laptop advertised as having 8 GB has 8,589,934,592 bytes of memory: 8.59×10⁹ B, or 8 GiB. ^[15]

See also

• Binary prefix
• Gigabit Ethernet
• SI prefix
• List of commonly used taxonomic affixes
• RKM code