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

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

  1. 1,180,591,620,717,411,303,424 bytes - 1024 times 1024 times 1024 times 1024 times 1024 times 1024 times 1024, or 270. This is 1024 times a exabyte. This is the definition used in computer science and computer programming
  2. 1,000,000,000,000,000,000,000 bytes - or 10 21.
See integral data type.

A yottabyte is 1024 times a zettabyte.

To clarify the meaning(1) above, 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). They did not provide a name for this number, although, it would probably be zebibyte. This naming convention has not, as of 2003, been widely adopted.

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