A zettabyte is a collection of about 1 sextillion bytes, which is around 1,000 exabytes.
In the metric system, zetta is a prefix for 1 sextillion, or 1021. So in some cases, a zettabyte is defined as 1 sextillion, or 1,000,000,000,000,000,000,000 bytes.
But because computers work in binary, computer scientists usually define a zettabyte as 1,180,591,620,717,411,303,424 (10247 or 270) bytes. This works out to 1,024 exabytes.
The abbreviation for zettabyte is ZB in both the metric system (1,000,000,000,000,000,000,000 bytes) and the binary system (1,180,591,620,717,411,303,424 bytes).
Some groups have proposed the name zebibyte for a unit of 1,180,591,620,717,411,303,424 bytes to prevent confusion. The abbreviation for zebibyte is ZiB.