Giga is a unit prefix in the metric system denoting a factor of a billion. It has the symbol G. Giga is derived from the Greek word γίγας, meaning "." 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 , although such use is inconsistent, contrary to standards and has been discouraged by the standards organizations. The inconsistency is that gigabit is never used with the binary interpretation of the prefix, while gigabyte is sometimes used this way. The binary prefixgibi has been adopted for 230, while reserving giga exclusively for the metric definition.
Pronunciation
In English, the prefix giga can be pronounced , or . 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. A prominent example 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 by the German humorous poet Christian Morgenstern that appeared in the third edition of his Galgenlieder. This suggests that a hard German was originally intended as the pronunciation. Self was unable to ascertain when the pronunciation came into occasional use, but claimed that as of 1995 it had returned to . In 1998, a poll by the phonetician John C. Wells found that 84% of Britons preferred the pronunciation of gigabyte starting with , 9% with , 6% with , and 1% with .
Common usage
gigahertz—clock rate of a CPU, for instance, 3 GHz =
gigabit—bandwidth of a network link, for instance, 1 Gbit/s =.
gigabyte—for instance, for hard disk capacity, 120 GB = ;
gigayear or gigaannum—one billion years, sometimes abbreviated Gyr, but the preferred usage is Ga.
Binary prefix
The notation can represent 1,073,741,824 bytes or 1,000,000,000 bytes. Under the IEC 60027-2 A.2 and ISO/IEC 80000 standards, the correct notation of 230 is gibi. So one gibibyte is 1,073,741,824 bytes or. Despite international standards, the use of = 230 B is widespread. A laptop advertised as having has 8,589,934,592 bytes of memory:, or.
