title: Differences between compiling for i386 vs x86_64 in Xcode?
body: <p>What are the differences between compiling a Mac app in Xcode with the Active Architecture set to i386 vs x86_64 (chosen in the drop down at the top left of the main window)? In the Build settings for the project, the Architecture options are Standard (32/64-bit Universal), 32-bit Universal, and 64-bit Intel. Practically, what do these mean and how does one decide?</p>
  
  <p>Assume one is targeting OS X 10.5 and above. I see in the Activity Monitor that compiling for x86_64 results in an app that uses more memory than one compiled for i386. What is the advantage?  I know 64-bit is "the future", but given the higher memory usage, would it make sense to choose 32-bit ever?</p>