Typical computers can be described as either 32-bit or 64-bit, depending on the architecture used in the computer's processor. The number of bits usually corresponds to the size of the registers the processor uses to store data. Windows 7 is available in both 32-bit and 64-bit editions, and while the 32-bit version of Windows will run on a 64-bit system, the 64-bit version of Windows will not run on a 32-bit system. You can find out whether your computer is 32-bit or 64-bit using a built-in performance utility.
Click your computer's "Start" button and type "Performance Information" (without quotes).
Click the "Performance Information and Tools" entry in the "Control Panel" section of the results.
Click "View and print detailed performance and system information" underneath the large icon indicating your computer's base score.
Look for a "64-bit capable" entry in the "System" section of the report. If the "64-bit capable" entry is "No," your computer is a 32-bit computer. If it is "Yes" or the entry is not present, your computer is a 64-bit computer.