Your a loving idiot thats called an operation system. An operating system is what you computer runs and it has nothing to do with 64 bit or 32 bit. Lets say i run in Windows XP service pack 2. That would be for my computer Windows XP Servicepack 2 64-bit.
You're a moron.
Compatibility mode makes the program run like you have that bit and OS.
I got Age of Empires 2 on my computer when I ran the setup in compatibility mode, and 64-bit computers were either nonexistant or not used enough to be for games.