# Peta

This article describes the SI prefix peta. For other meanings, including People for the Ethical Treatment of Animals see Peta (disambiguation).

In physics and mathematics, peta (symbol: P) is a prefix in the SI system of units denoting 1015, or 1 000 000 000 000 000. For example:

1 petametre = 1015 metres

1 petasecond = 1015 seconds

Adopted in 1975, it comes from the Greek πέντε, meaning five, because it is equal to 10005. (It is based on the model of tera, coming from the Greek for 'monster': tetra- is from the Greek for four and so peta, coming from penta-, misses the third letter, n, out.)

In computer science peta can sometimes mean 1 125 899 906 842 624 (10245 or 250), instead of 1 000 000 000 000 000, especially when used to prefix the byte, giving a petabyte. To resolve this ambiguity, the term pebibyte has been suggested to mean 250 bytes. However, this term is not yet widely used.

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