Note that 'peta' now officially means 10
15 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. So
1 petabyte = 1 PB = 1015 bytes
1 pebibyte = 1 PiB = 10245 bytes
These new prefixes were created in December 1998 by the International Electrotechnical Commission: see the node prefixes for binary multiples for fuller explanation.
It is permissible to use 'petabyte' to mean pebibyte on a temporary basis until industry standards have shifted to the new terms.
The prefix 'peta' was originally adopted by the fifteenth CGPM of the SI in 1975. It comes from an alteration of the Greek for 'five'.
Note the symbol for peta is a normal capital P, not a rho as stated above.