A 64-bit processor has a 64 bit data bus. The data bus, accumulator(s), & registers are 64 bits (8 bytes) wide. Most processors will have address busses that are wider than their data busses. For example most of the old 8-bit processors had 16 address bits. At least one of the "new" 64 bit processors has a 48-bit address bus... I don't remember which one.
