"32/64-bit" refers to the width of the address bus and registers used by the CPU core. A 64-bit CPU has a 64-bit wide address bus and 64- bit wide registers. CPUs access data in the RAM by using the address bus. The breadth of the bus influences the amount of RAM that can be addressed. A 32-bit bus allows a maximum of 4 GB of RAM to be accessed. A 64-bit CPU, obviously, allows for more RAM to be used - about 16 exabytes (1 exabyte = 1,000,000,000 gigabytes, approximately). A 64-bit register can store 64 bits of data simultaneously. To fully utilise a 64-bit CPU, the operating system and application need to support the 64-bit mode of operation.