A yottabyte is a collection of about 1 septillion bytes, which is around 1,000 zettabytes.
In the metric system, yotta is a prefix for 1 septillion, or 1024. So in some cases, a yottabyte is defined as 1 septillion, or 1,000,000,000,000,000,000,000,000 bytes.
But because computers work in binary, computer scientists usually define a yottabyte as 1,208,925,819,614,629,174,706,176 (10248 or 280) bytes. This works out to 1,024 zettabytes.
The abbreviation for yottabyte is YB in both the metric system (1,000,000,000,000,000,000,000,000 bytes) and the binary system (1,208,925,819,614,629,174,706,176 bytes).
Some groups have proposed the name yobibyte for a unit of 1,208,925,819,614,629,174,706,176 bytes to prevent confusion. The abbreviation for yobibyte is YiB.