How to check what kind of processor you have (CPU) and what operating system can I run on it?
An X64 has a 64 bit microprocessor, whereas an X86, derived from the old 8086 PC, has a 32 bit microprocessor. A 32 bit machine and/or OS (operating system) is limited to about 3.55GB of memory, and an X64 is limited to about 17,179,869,184 gigabytes, 17,179,869 terabytes, or about 16 exabytes of RAM. Also a 32-bit CPU cannot run an 64-bit OS.
So, how to check your CPU:
Since you cannot run WIndows7-64x on a 32-bit machine lets look at windows 7. From the Start icon on the toolbar select Control Panel. Look for Hardware and SOund and select View devices and printers. Double-click your computer (will be labeled with your machine name). A Properties window pops-up with two tabs, select the Hardware tab. Look for a name starting with ACPI, with Type of Computer. If it says ACPI x64-based PC you know you have a 64-bit machine, CONGRATULATIONS! You can now install a 64-bit OS like Vista-64 or Windows7-64 and run any of your old software as the new 64-bit OS "knows" (is compatible) how to run the 32-bit apps.
What about memory?
If you want to install more than 4GB or RAM you will need to have a 64-bit CPU and also run a 64-bit OS otherwise you are wasting your money.