Developments in central processing unit architecture have enabled CPU manufacturers to integrate multiple processors, called cores, into a single unit. Computers have been using 32-bit registers for over a decade, but modern CPU cores utilize 64-bit architecture in order to make use of higher RAM capacities. Determining whether to go with a 32-bit or 64-bit multi-core CPU, however, depends on your needs.
Basics - Three main components determine the performance of a CPU: the front-side bus, or data bus, address bus and internal registers. The FSB carries data to and from the processor and the memory controller hub, and determines how fast data is sent between these two components. The address bus carries information that explains where in the memory data is being sent or received. The internal registers specify the amount of data the CPU can process at one time, as well as how the CPU handles this data. The size of the register determines what architecture, or instruction set, the processor can use. A 64-bit CPU, in other words, can handle a maximum of 64-bits in a single register at a time; 32-bit CPUs are limited to 32-bit instructions per register, and so on. 64-bit CPUs can run 32-bit or 64-bit operating systems; 32-bit CPUs can only run 32-bit operating systems.