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Giga (/ˈɡɪɡə/ or /ˈdʒɪɡə/) is a unit prefix in the metric system denoting a factor of a (short-form) billion (10⁹ or 1000000000). It has the symbol G.

Giga is derived from the Greek γίγας, 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 Conference in 1947: "The following prefixes to abbreviations for the names of units should be used: G giga 10⁹×".

When referring to information units in computing, such as gigabyte, giga may sometimes mean 1073741824 (2³⁰), although such use is inconsistent, contrary to standards and has been discouraged by the standards organizations.^[1]^[2] The inconsistency is that gigabit is never (or very rarely) used as a binary prefix, while gigabyte is sometimes used as one. The binary prefix gibi has been adopted for 2³⁰, while reserving giga exclusively for the metric definition.

Pronunciation

In English, the initial g of giga can be pronounced /ɡ/ (a hard g as in giggle), or /dʒ/ (a soft g as in giant, like a j sound, which shares its Greek root).^[3]

This latter pronunciation was formalised 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 claimed that as of 1995 it had died out.^[5]

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).^[6]

Common usage

gigabyte—for instance, for hard disk capacity, 120 GB = 120000000000bytes; for file sizes 1 GB is often 1073741824 or 2³⁰ bytes, more properly termed a gibibyte (GiB) to eliminate ambiguity. The difference is rooted in base 10 and base 2 enumeration, and is also the reason why hard drives advertised as a certain capacity have less than that capacity when installed (as hard drives are advertised in gigabytes or terabytes (base 10) whereas computers format data in gibibytes or tebibytes (base 2, powers of 2). See Hard disk units of storage capacity.
gigahertz—clock rate of a CPU, for instance, 3 GHz = 3000000000Hz
gigabit—bandwidth of a network link, for instance, 1 Gbit/s = 1000000000bit/s.
gigayear or gigaannum—one billion (10⁹) years, sometimes abbreviated Gyr, but the preferred usage is Ga.

SI prefixes
v
t
e
Prefix		Base 10	Decimal	Adoption ^{[nb 1]}
Name	Symbol	Base 10	Decimal	Adoption ^{[nb 1]}
quetta	Q	10³⁰	1000000000000000000000000000000	2022^[7]
ronna	R	10²⁷	1000000000000000000000000000	2022^[7]
yotta	Y	10²⁴	1000000000000000000000000	1991
zetta	Z	10²¹	1000000000000000000000	1991
exa	E	10¹⁸	1000000000000000000	1975^[8]
peta	P	10¹⁵	1000000000000000	1975^[8]
tera	T	10¹²	1000000000000	1960
giga	G	10⁹	1000000000	1960
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	1960
femto	f	10⁻¹⁵	0.000000000000001	1964
atto	a	10⁻¹⁸	0.000000000000000001	1964
zepto	z	10⁻²¹	0.000000000000000000001	1991
yocto	y	10⁻²⁴	0.000000000000000000000001	1991
ronto	r	10⁻²⁷	0.000000000000000000000000001	2022^[7]
quecto	q	10⁻³⁰	0.000000000000000000000000000001	2022^[7]
Notes ^ Prefixes adopted before 1960 already existed before SI. The introduction of the CGS system was in 1873.

In popular culture

Films and television

The DeLorean time machine in the 1985 American science fiction film Back to the Future requires 1.21 gigawatts (pronounced "one point twenty-one Jigga-watts") of electrical power to travel through time, according to its inventor, Doc Brown.^[9]

References

^ "§3.1 SI prefixes". The International System of Units (SI) (PDF) (in French/English) (8th edition ed.). Paris: STEDI Media. 2006. p. 127. ISBN 92-822-2213-6. 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. {{cite book}}: |edition= has extra text (help)CS1 maint: unrecognized language (link)
^ 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
^ Wells, J.C. (1998). LPD pronunciation preference poll 1998.
^ ^a ^b "On the extension of the range of SI prefixes". 18 November 2022. Retrieved 5 February 2023.
^ "Metric (SI) Prefixes". NIST.
^ Back to the Future (1985). Trivia. IMDB (2013).

External links

BIPM website

[7] Prefixes adopted before 1960 already existed before SI. The introduction of the CGS system was in 1873.

[BIPM-1] "§3.1 SI prefixes". The International System of Units (SI) (PDF) (in French/English) (8th edition ed.). Paris: STEDI Media. 2006. p. 127. ISBN 92-822-2213-6. 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. {{cite book}}: |edition= has extra text (help)CS1 maint: unrecognized language (link)

[NIST-2] NIST Guide for the Use of the International System of Units (Appendix D. ref 5)

[3] A Practical Guide to the International System of Units, U.S. Metric Association, Feb 2008

[4] NBS Special Publication 304 & 304A, revised August 1981, "A Brief History of Measurement Systems"

[5] Kevin Self, April 1995, "Technically speaking", Spectrum

[6] Wells, J.C. (1998). LPD pronunciation preference poll 1998.

[newUnitAdoption-8] "On the extension of the range of SI prefixes". 18 November 2022. Retrieved 5 February 2023.

[9] "Metric (SI) Prefixes". NIST.

[10] Back to the Future (1985). Trivia. IMDB (2013).

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@@ Line 5: / Line 5: @@
 ''Giga'' is derived from the [[Greece|Greek]] γίγας, meaning '[[wiktionary:giant|giant]]'. The [[Oxford English Dictionary]] reports the earliest written use of ''giga'' in this sense to be in the Reports of the [[International Union of Pure and Applied Chemistry|IUPAC]] 14th Conference in 1947: "The following prefixes to abbreviations for the names of units should be used: G giga 10<sup>9</sup>×".
-When referring to information units in [[computing]], such as [[gigabit]] or [[gigabyte]], ''giga'' may sometimes mean {{gaps|1|073|741|824}} (2<sup>30</sup>), although such use is contrary to standards and has been discouraged by the [[standards organization]]s.<ref name="BIPM">{{cite book
+When referring to information units in [[computing]], such as [[gigabyte]], ''giga'' may sometimes mean {{gaps|1|073|741|824}} (2<sup>30</sup>), although such use is inconsistent, contrary to standards and has been discouraged by the [[standards organization]]s.<ref name="BIPM">{{cite book
 |title=The International System of Units (SI)
 |url=http://www1.bipm.org/utils/common/pdf/si_brochure_8.pdf
@@ Line 19: / Line 19: @@
 |chapter=§3.1 SI prefixes
 |quote=[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 2<sup>10</sup>, 2<sup>20</sup>, 2<sup>30</sup>, 2<sup>40</sup>, 2<sup>50</sup>, and 2<sup>60</sup> 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 = 2<sup>10</sup> 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.
-}}</ref><ref name="NIST">[http://physics.nist.gov/cuu/pdf/sp811.pdf NIST Guide for the Use of the International System of Units (Appendix D. ref 5)]</ref> The [[binary prefix]] [[gibi]] has been adopted for 2<sup>30</sup>, while reserving giga exclusively for the metric definition.
+}}</ref><ref name="NIST">[http://physics.nist.gov/cuu/pdf/sp811.pdf NIST Guide for the Use of the International System of Units (Appendix D. ref 5)]</ref> The inconsistency is that gigabit is never (or very rarely) used as a binary prefix, while gigabyte is sometimes used as one. The [[binary prefix]] [[gibi]] has been adopted for 2<sup>30</sup>, while reserving giga exclusively for the metric definition.
 ==Pronunciation==