Exabyte

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An exabyte (derived from the SI prefix exa- ) is a unit of measurement in computers of one million million million bytes. Its abbreviation is EB.

Because of irregularities in definition and usage of the kilobyte, the exact number in common practice could be either of the following:

1. 1,000,000,000,000,000,000 bytes - 1000⁶, or 10¹⁸.
2. 1,152,921,504,606,846,976 bytes - 1024⁶, or 2⁶⁰. This is the definition most often used in computer science and computer programming.

As of 2004, exabytes of data are almost never encountered in a practical context. For example the total amount of printed material in the world is estimated to be around a fifth of an exabyte. Exabytes may also appear to be encountered if a computer's file system is corrupt and displaying incorrect file sizes. However, one may hear of 16 exabytes (or 18 times 10¹⁸) of address space when discussing various 64-bit architectures.

To clarify the distinction between decimal and binary prefixes, the International Electrotechnical Commission (IEC), a standards body, in 1998 defined new prefixes by combining the International System of Units (SI) prefixes with the word "binary" (see Binary prefix). Thus meaning (2) is called by the IEC an exbibyte (EiB), and meaning (1) is called by the IEC an exabyte. This naming convention has not, as of 2004, been widely adopted.

An exabyte is 1000 petabytes using the first definition, while an exbibyte is 1024 pebibytes using the second definition.

1 Petabyte = 1000 Terabyte

1 Exabyte = 1000 Petabyte

1 Zettabyte = 1000 Exabyte

The prefix "exa" is an alteration of "hexa", the Greek word for 6, because in 10¹⁸ = (10³)⁶.

See also

• zettabyte
• exbibyte
• binary prefix
• integral data type

External links

• http://www.quinion.com/words/turnsofphrase/tp-kib1.htm
• http://www.nist.gov/public_affairs/techbeat/tb9903.htm

Exabyte is also the name used for a brand of digital tape cartridges from NCR Corporation. Of course, no one has yet made a cartridge capable of holding a true exabyte.

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