The processor is the hardware component at the center of a modern computer. The processor fetches data from memory and copies it back into memory after having performed computations on it. In the current consumer market, there are processors that can operate on pieces of data that are up to 32 bits in size; more modern processors can operate on 64 bits at a time. The number of bits is an unchangeable characteristic of a given processor, encoded in its circuitry. 64-bit processors can run 32- or 64-bit operating systems (thanks to backwards-compatibility built into their instruction sets), but 32-bit processors can only run 32-bit operating systems. You can easily determine whether your processor and your operating system are running in 32- or 64-bit mode.
Click "Start," then click "Run." A Run window will come up. Type "msinfo32.exe" into the Run window, then press "Enter." A System Information window will come up.
Click "System Summary," then search for the line corresponding to the version of Microsoft Windows installed on the computer. If it contains the indicator "x86," then you are running 32-bit Windows. If it contains the indicator "x64," you are running 64-bit Windows.
Click "Hardware Resources," then search for the line corresponding to the processor ("CPU") in the system. If it contains the indicator "x64," you have a 64-bit processor. If it contains the indicator "x86," you have a 32-bit processor that can only run 32-bit software.