A large unit of computer data storage, equal to 260 bytes. The prefix "exa" means one billion billion, or one quintillion, which is a decimal term. Two to the sixtieth power is actually 1,152,921,504,606,846,976 bytes in decimal, or somewhat over a quintillion (or 1018) bytes. However, it's common to say that an exabyte is approximately one quintillion bytes. In decimal terms, an exabyte is a billion gigabytes.