Giga-

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For other uses, see Giga (disambiguation).

Giga (/ˈɪɡə/ or /ˈɡɪɡə/) 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 with the binary interpretation of the prefix, while gigabyte is sometimes used this way. The binary prefix gibi has been adopted for 230, while reserving giga exclusively for the metric definition.

Pronunciation[edit]

In English, the initial g of giga can be pronounced /ɡ/ (a hard g as in giggle), or // (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[edit]

  • 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.
  • gigahertzclock rate of a CPU, for instance, 3 GHz = 3000000000Hz
  • gigabitbandwidth 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.
Metric prefixes
Prefix Symbol 1000m 10n Decimal English word Since[n 1]
short scale long scale
yotta Y  10008  1024 1000000000000000000000000  septillion  quadrillion 1991
zetta Z  10007  1021 1000000000000000000000  sextillion  thousand trillion 1991
exa E  10006  1018 1000000000000000000  quintillion  trillion 1975
peta P  10005  1015 1000000000000000  quadrillion  thousand billion 1975
tera T  10004  1012 1000000000000  trillion  billion 1960
giga G  10003  109 1000000000  billion  thousand million 1960
mega M  10002  106 1000000             million 1960
kilo k  10001  103 1000             thousand 1795
hecto h  10002/3  102 100             hundred 1795
deca da  10001/3  101 10             ten 1795
 10000  100 1             one
deci d  1000−1/3  10−1 0.1             tenth 1795
centi c  1000−2/3   10−2 0.01             hundredth 1795
milli m  1000−1  10−3 0.001             thousandth 1795
micro µ  1000−2  10−6 0.000001             millionth 1960
nano n  1000−3  10−9 0.000000001  billionth  thousand millionth 1960
pico p  1000−4  10−12 0.000000000001  trillionth  billionth 1960
femto f  1000−5  10−15 0.000000000000001  quadrillionth  thousand billionth 1964
atto a  1000−6  10−18 0.000000000000000001  quintillionth  trillionth 1964
zepto z  1000−7  10−21 0.000000000000000000001  sextillionth  thousand trillionth 1991
yocto y  1000−8  10−24  0.000000000000000000000001  septillionth  quadrillionth  1991
  1. ^ The metric system was introduced in 1795 with six prefixes. The other dates relate to recognition by a resolution of the CGPM.

See also[edit]

References[edit]

  1. ^ "§3.1 SI prefixes" (PDF). The International System of Units (SI) (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." 
  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.

External links[edit]