What's the difference? Quoting from the Microsoft web site: "The terms 32-bit and 64-bit refer to the way a computer's processor (also called a CPU), handles information. The 64-bit version of Windows handles large amounts of random access memory (RAM) more effectively than a 32-bit system."
Most Windows-based computers sold since 2010 run the 64-bit version.
How do I determine what I'm running?