Giga is a unit prefix in the metric system indicating multiplication of a unit by 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 gigabit or gigabyte, giga may sometimes mean 1073741824 (230), although such use is contrary to standards and has been discouraged by the standards organizations. The binary prefix gibi has been adopted for 230, while reserving giga exclusively for the metric definition.
In English, the initial g of giga can be pronounced /ɡ/ (a hard g as in giggle), or /dʒ/ (a soft g as in its Greek root's meaning, giant).
This latter pronunciation was formalized 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. 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.
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