What's the difference between i386, armv7 and armv7s?

I would like to know the difference between those architectures in Xcode because I need to know how I understand that a library can compile correctly for iOS Simulator and also for iPhone 5, iPhone 4s and iPhone 4. Or just for one of those.

i386: Typically MacOSX (I am not sure whether Simulator is included here or no).
arm6: old iPhones.
arm7: iPhone4/4S.
arm7s: additional instructions for arm7 to make good use of iPhone 5 processor.

Hope this helps. Compiling libraries to support all platforms sometimes is very frustrating and tedious task. Good luck!