Because of irregularities in definition and usage of the kilobyte, the exact number could be any one of the following:
A petabyte is 1024 times an terabyte.
To clarify the meaning(1) above, the International Electrotechnical Commission (IEC), a standards body, in 1997 proposed short unions of the International System of Units (SI) prefixes with the word "binary." Thus meaning (1) would be called a tebibyte. (Gi) This naming convention has not been widely accepted.
links: http://www.quinion.com/words/turnsofphrase/tp-kib1.htm http://www.nist.gov/public_affairs/techbeat/tb9903.htm