What is "exa-"

pre. In the International System of Units and other metric systems of units, multiplying the unit to which it is attached by 10¹⁸. Symbol: E

Exa is a decimal unit prefix in the metric system denoting 10 or . 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 , used as a prefix , meaning six (like hexa-), because it is equal to 1000.

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 = 10 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)