# Peta-

Peta- (symbol: P) is a prefix in the metric system denoting 1015 or 1000000000000000. For example:

1 petametre = 1015 metres
1 petasecond = 1015 seconds
1 petabyte = 1015 bytes

Adopted in 1975,[1] it was derived from the Greek πέντε, meaning "five", because of the five in 10005, for which it stands. The peta- prefix is similar to the penta- prefix (for "five"), but without the letter n. This omission is modelled on the way the similar tera- prefix (actually from Greek τέρας = 'monster') for 10004 seems to omit a letter from the tetra- prefix (for "four").

Examples:

In computer science peta- can sometimes mean 1125899906842624 (10245 or 250), instead of 1000000000000000, especially when used to prefix the byte, giving a petabyte. To resolve this ambiguity, the term pebibyte has been suggested to mean 250 bytes.

Metric prefixes
Prefix Symbol 1000m 10n Decimal English word[n 1] Since[n 2]
yotta Y  10008  1024 1000000000000000000000000 septillion 1991
zetta Z  10007  1021 1000000000000000000000 sextillion 1991
exa E  10006  1018 1000000000000000000 quintillion 1975
peta P  10005  1015 1000000000000000 quadrillion 1975
tera T  10004  1012 1000000000000 trillion 1960
giga G  10003  109 1000000000 billion 1960
mega M  10002  106 1000000 million 1960
kilo k  10001  103 1000 thousand 1795
hecto h  10002/3  102 100 hundred 1795
deca da  10001/3  101 10 ten 1795
10000  100 1 one
deci d  1000−1/3  10−1 0.1 tenth 1795
centi c  1000−2/3   10−2 0.01 hundredth 1795
milli m  1000−1  10−3 0.001 thousandth 1795
micro µ  1000−2  10−6 0.000001 millionth 1960
nano n  1000−3  10−9 0.000000001 billionth 1960
pico p  1000−4  10−12 0.000000000001 trillionth 1960
femto f  1000−5  10−15 0.000000000000001 quadrillionth 1964
atto a  1000−6  10−18 0.000000000000000001 quintillionth 1964
zepto z  1000−7  10−21 0.000000000000000000001 sextillionth 1991
yocto y  1000−8  10−24  0.000000000000000000000001 septillionth 1991
1. ^ This table uses the short scale.
2. ^ The metric system was introduced in 1795 with six prefixes. The other dates relate to recognition by a resolution of the CGPM.