Is my CPU 32 or 64 bit ?

Go to Start > Run > Type msinfo32.exe (for Windows XP or older) Go to Start -> Type msinfo32.exe (for Windows Vista/7) From the System Information page under System Type you will find out whether it is x64-based PC or x32-based. 32-bit and 64-bit represent the Data Bus width that are between the Memory (RAM) and the Processor. 64-bit has the capability of carrying data twice the width of 32-bit. So its more efficient and has higher max-memory limit. To use a 64 bit CPU you at its max, you need a 64 bit version of the OS as well (available as Windows XP/Vista/7 64-bit or later)

64 bit simply processes more information, and has a better finished product. However it takes more memory and does not work well for underpowered systems. 4 gigs of ram or more preferred. Even if your processor can handle 64 bit, it does not mean your mother board, or graphics card can. To see if you are running 64bit in windows, go to computer, on right click in that window with nothing selected and choose properties. Should be under system type.

x86 is 32-bit, x64 is 64-bit. Software which requires a 64-bit operating system does not function on a 32-bit operating system. The other way around however is not an issue (in 99% of all cases). A 32-bit operating system supports up to 4GB of RAM, of which only 3-and-a-bit-GB of RAM will be usable by the operating system then. A 64-bit operating system can allocate more than 4GB of RAM, so if you have 4GB of RAM or more, a 64-bit operating system is advised. When you have less than 4GB of RAM, a 32-bit operating system will perform slightly better, making a 32-bit operating system the better choice on slower or older hardware. You cannot upgrade from a 32-bit operating system to a 64-bit operating system; this requires a reinstallation of your computer. I hope this clears things up for you a bit.

x86 is 32 bit but x86-64 is 64 bit.