Giga-

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.

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.

^ "giga-, comb. form". Oxford English Dictionary. October 2011.
^ "Wireless Engineer, 1932, issue 05, p. 252" (PDF). Archived (PDF) from the original on 2022-03-28. Retrieved 2022-03-28.
^ "§3.1 SI prefixes". The International System of Units (SI) (PDF) (in French and English) (8th ed.). Paris: STEDI Media. 2006. p. 127. ISBN 92-822-2213-6. Archived (PDF) from the original on 2006-08-13. 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)

[1] "giga-, comb. form". Oxford English Dictionary. October 2011.

[2] "Wireless Engineer, 1932, issue 05, p. 252" (PDF). Archived (PDF) from the original on 2022-03-28. Retrieved 2022-03-28.

[BIPM-3] "§3.1 SI prefixes". The International System of Units (SI) (PDF) (in French and English) (8th ed.). Paris: STEDI Media. 2006. p. 127. ISBN 92-822-2213-6. Archived (PDF) from the original on 2006-08-13. 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-4] NIST Guide for the Use of the International System of Units (Appendix D. ref 5)

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