The prefix "zetta" is part of the International System of Units (SI) and refers to 1021 units. Hard disk manufacturers label their products in SI, which may confuse some people in the IT field. The ISO, IEEE and the IEC all recommend using the unit zebibyte, which signifies 270 bytes and is more accurate for the measure of bytes.
Two interpretations can be made using the two standards:
Using SI, one zettabyte is equivalent to 1,000 exabytes or 1,000,000,000,000,000,000,000 or 1021 bytes.
Using traditional binary measurement, one zettabyte is equivalent to 1,180,591,620,717,411,303,424 bytes, that’s 270 bytes, also equivalent to 1 zebibyte (ZiB).