What is the sense behind ZFS's limits?

According to Wikipedia , ZFS has the following limits: * **Max. volume size**: 256 trillion yobibytes (2128 bytes) * **Max. file size**: 16 exbibytes (264 bytes) * **Max. number of files**: * Per directory: 248 * Per file system: unlimited * **Max. filename length**: 255 ASCII characters (fewer for multibyte character encodings such as Unicode) Why does it have these limits? What internally limits these things? Why couldn't ZFS have a theoretically unlimited volume size, or filename length, and so on?