A zettabyte is 2 to the 70th power, or 1,180,591,620,717,411,303,424 bytes.
It can be estimated as 10 to the 21st power, or 1,000,000,000,000,000,000,000 bytes. A zettabyte is 1,024 exabytes and precedes the yottabyte unit of measurement. Because of the enormous size of a zettabyte, this unit is almost never used. The prefix zetta comes from "Zeta," which is the sixth letter of the Greek alphabet.