How do you tell the difference between 64 bit and 32 bit?

A 32-bit system has a maximum 2^32 unique memory addresses, which is 4,294,967,296 addresses in total. Each address refers to a byte (the smallest unit of storage), thus this allows a maximum address space of 4 gigabytes. Each additional bit doubles the number of available addresses, thus a 64-bit system supports a maximum of 18,446,744,073,709,551,616 bytes, which is more memory than exists on the planet. Note that the length of a byte is system-defined.