Mega is a unit prefix in the metric system denoting a factor of one million (106 or 1000000). It was confirmed for use in the International System of Units (SI) in 1960. Mega comes from the Greek μέγας megas, meaning "great".
Other common examples of usage
- megapixel - 1 million pixels in a digital camera
- one megatonne (of TNT), equivalent to approx. 4 Petajoules; is the approximate energy released on igniting one million tonnes of TNT, and is a unit often used in measuring the explosive power of nuclear weapons.
- megahertz — frequency of electromagnetic radiation for radio and television broadcasting, GSM, etc. 1 MHz = 1,000,000 Hz.
When units occur in exponentiation, such as in square and cubic forms, any size prefix is considered part of the unit, and thus included in the exponentiation.
- 1 Mm2 means one square megametre or the size of a square of 1000000m by 1000000m or 1012m2, and not 1000000square metres (106 m2).
- 1 Mm3 means one cubic megametre or the size of a cube of 1000000m by 1000000m by 1000000m or 1018 m3, and not 1000000cubic metres (106 m3)
In computing, mega may sometimes denote 1,048,576 (220) of information units (example: a megabyte, a megaword), but denotes 1000000 (106) units of other quantities, for example, transfer rates: 1megabit/s = 1000000bit/s. The prefix mebi has been suggested as a prefix for 220 to avoid ambiguity.
- The metric system was introduced in 1795 with several metric prefixes, of which, however, only six were adopted as SI prefixes by the 11th CGPM conference in 1960, whereas myria (ma, 104) and myrio (mo, 10-4) as well as double and demi were not adopted. In 1873, micro and mega were recommended by the British Association for the Advancement of Science. The other dates relate to recognition by a resolution of the CGPM.
- "[http://dictionary.oed.com/cgi/entry/00304790 mega-]". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005. (Subscription or UK public library membership required.)
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