Petabyte

A petabyte is a unit of measurement in computers of approximately one thousand million million (American quadrillion) bytes.

Because of irregularities in definition and usage of the kilobyte, the exact number could be any one of the following:

1. 1,125,899,906,842,624 bytes - 1024 times 1024 times 1024 times 1024 times 1024, or 2⁵⁰. This is 1024 times a terabyte. This is the definition used in computer science and computer programming
2. 1,000,000,000,000,000 bytes - or 10 ¹⁵.

See integral data type.

A exabyte is 1024 times an petabyte.

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To clarify the meaning(1) above, the International Electrotechnical Commission (IEC), a standards body, in 1997 proposed short unions of the International System of Units (SI) prefixes with the word "binary." Thus meaning (1) would be called a pebibyte. (Gi) This naming convention has not been widely accepted.

links: http://www.quinion.com/words/turnsofphrase/tp-kib1.htm

http://www.nist.gov/public_affairs/techbeat/tb9903.htm