Almost all of today’s PC-based CPUs are 64-bit; it’s a type of CPU architecture that incorporates registers that are 64 bits wide. These registers, or temporary storage areas, allow the CPU to work with and process 64-bit data types and provide support for address space in the terabytes. 64-bit CPUs have been available for PCs since 2003. Examples of 64-bit CPUs include the AMD FX and Intel Core series of CPUs.
A little history: The predecessor to the 64-bit CPU was the 32-bit CPU. Intel started developing well-known 32-bit CPUs as early as 1985 with the
386DX CPU (which ran at a whopping 33 MHz!) and AMD did likewise in 1991 with the Am386. A 32-bit CPU can’t support nearly as much address space as a 64-bit CPU; 32-bit is limited to 4 GB. Most editions of Windows are available in both 32-bit and 64-bit versions