An International System of Units (SI, a.k.a. metric) prefix denoting 10 to the 21st power (10e+21 or 10^21). It's symbol is Z.

In other words, Z 's multiplier is 1,000,000,000,000,000,000,000 (a.k.a. a sextillion).

see also: Standard SI prefixes

Zetta, similar to the Greek "zeta", is the last letter of the latin alphabet. This prefix is used in the SI system, in words such as zettanewton.

This node was previously deleted for being factually wrong, but I am resubmitting it, having found this information in many places.

Note that 'zetta' now officially means 1021 even in the context of data processing. The prefixes kilo, mega, giga, tera, peta, exa, zetta, yotta always refer to powers of 10.

To refer to powers of 210 (powers of 1024), use the new binary prefixes kibi, mebi, gibi, tebi, pebi, and exbi. That is as high as they go; there are no official prefixes 'zebi' or 'yobi'.

These new prefixes were created in December 1998 by the International Electrotechnical Commission: see the node prefixes for binary multiples for fuller explanation.

The prefix 'zetta' was originally adopted by the nineteenth CGPM of the SI in 1991, along with yotta, zepto, and yocto.

The name comes from the Latin root for seven, sept-. It does not refer to letters of the Latin alphabet. The last four suffixes are alterations of Greek penta- 'five', hexa- 'six', and Latin sept- 'seven' and oct- 'eight'.

The last two letters Y and Z of the Latin alphabet were not used in Latin; they were purely used in writing borrowed Greek words. They would have had their Greek names ypsilon and zeta. There is no ground for doubling the T in zeta, and the idea that Y was called anything like yotta is wholly unfounded.

This error can be found on the Web, however: a JPL site has a brief (and very crude, unscientific) glossary of abbreviations, which also contains other errors (e.g. they say giga- is from Latin, when it's a Greek borrowing; they use the capitalization ExaHertz... you could probably find more).

This was the factual error for which I originally deleted SlickCow's write-up; but as they found it with JPL/NASA's authority they can't be blamed for believing it. It is however definitely wrong.

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