byte32 = 32 bytes = 64 hex

0x{64までいける！}

• bytes: dynamic sized byte sequence.
• string: dynamic sized unicode string assumed to be UTF-8 encoded.
• <type>[]: a variable-length array of elements of the given type.

As a rule of thumb, use bytes for arbitrary-length raw byte data stringfor arbitrary-length string (UTF-8) data.

If you can limit the length to a certain number of bytes, always use one of bytes1 to bytes32 because they are much cheaper.

Why do Solidity examples use bytes32 type instead of string?

string >> dynamic

byte32 >> can understand maximam