Exa-

This article is about the SI prefix. For other uses, see Exa (disambiguation).

Exa is a decimal unit prefix in the metric system denoting 10¹⁸ or 1000000000000000000. It was added as an SI prefix to the International System of Units (SI) in 1975, and has the unit symbol E.

Exa comes from the Ancient Greek ἕξ, used as a prefix ἑξά-, meaning six (like hexa-), because it is equal to 1000⁶.

Examples:

• The total storage needed by Google Mail as of April 2012, ignoring backups and compression, is more than an exabyte (10,240 megabytes of storage per user multiplied by an estimated 260 million users).
• 1 EeV = 10¹⁸ electronvolts = 0.1602 joule
• 1 exasecond is approximately 32 billion years
• 1 exametre is approximately 110 light years
• 0.43 Es ≈ the approximate age of the Universe
• 1.6 Em—172 ± 12.5 light years—Diameter of Omega Centauri (one of the largest known globular clusters, perhaps containing over a million stars)

SI prefixes

Prefix Base 1000 Base 10 Decimal English word Adoption Name Symbol Short scale Long scale yotta Y  10008  1024 1000000000000000000000000  septillion  quadrillion 1991 zetta Z  10007  1021 1000000000000000000000  sextillion  trilliard 1991 exa E  10006  1018 1000000000000000000  quintillion  trillion 1975 peta P  10005  1015 1000000000000000  quadrillion  billiard 1975 tera T  10004  1012 1000000000000  trillion  billion 1960 giga G  10003  109 1000000000  billion  milliard 1960 mega M  10002  106 1000000  million  million 1873 kilo k  10001  103 1000  thousand  thousand 1795 hecto h  10002/3  102 100  hundred  hundred 1795 deca da  10001/3  101 10  ten  ten 1795  10000  100 1  one  one – deci d  1000−1/3  10−1 0.1  tenth  tenth 1795 centi c  1000−2/3   10−2 0.01  hundredth  hundredth 1795 milli m  1000−1  10−3 0.001  thousandth  thousandth 1795 micro μ  1000−2  10−6 0.000001  millionth  millionth 1873 nano n  1000−3  10−9 0.000000001  billionth  milliardth 1960 pico p  1000−4  10−12 0.000000000001  trillionth  billionth 1960 femto f  1000−5  10−15 0.000000000000001  quadrillionth  billiardth 1964 atto a  1000−6  10−18 0.000000000000000001  quintillionth  trillionth 1964 zepto z  1000−7  10−21 0.000000000000000000001  sextillionth  trilliardth 1991 yocto y  1000−8  10−24  0.000000000000000000000001  septillionth  quadrillionth 1991

See also

• 1 exametre
• Exabyte
• Exasecond
• Orders of magnitude (numbers)
• Metric prefix
• Binary prefix

References

• International Bureau of Weights and Measures (2006), The International System of Units (SI) (PDF) (8th ed.), ISBN 92-822-2213-6 

External links

• BIPM website
• Exa Corporation
• Exa Proxy Test