There are two versions of windows. . one is a standard 32 bit version, and the more modern version is a 64 bit version. If your pc is older than a couple years, more than likely you're still on a 32 bit machine/processor.
The terms 32-bit and 64-bit refer to the way a computer's processor (also called a CPU), handles information. The 32-bit and 64-bit versions of Windows are designed for use in computers with 32-bit or 64-bit processors, respectively.
A 64-bit computer can process twice as much information as a 32-bit computer, and can have significantly more random access memory (RAM). This makes a 64-bit computer a good choice if you're working with video, large database searches, or games and other programs that require complex calculations and a lot of memory. A 32-bit computer works very well for most programs, however. For example, spreadsheet programs, web browsers, and word processing programs will run at about the same speed on either a 32-bit or a 64-bit computer.