In computer architecture, 64-bit integers, memory addresses, or other data units are those that are at most 64 bits (8 octets) wide. Also, 64-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size.
For instance, many current machines with 32-bit processors use 64-bit buses (e.g. the original Pentium and later CPUs), and may occasionally be referred to as "64-bit" for this reason .
the main update with 64 bit processor is the larger memory support.
The emergence of the 64-bit architecture effectively increases the memory ceiling to 264 addresses, equivalent to 17,179,869,184 GiB, 17,179,869 terabytes, or about 16 exabytes of RAM
if you refer to the system bus then most today processor are 128 bit .
Hope this help