Source : WordNet®

petabyte
     n : a unit of information equal to 1,024 terabytes

Source : Free On-Line Dictionary of Computing

petabyte
     
         2^50 = 1,125,899,906,842,624 {bytes} = 1024
        {terabytes} or roughly 10^15 bytes.
     
        See {prefix}.
     
        (1996-08-12)