On Mac OS X Leopard and in Snow Leopard, Apple designed the kernel to run both 32 and 64-bit software natively with no compatibility layer running, and all supporting files and libraries can be organized in the same application bundle. That means developers can distribute a single installer that works on any Mac, and that users won't need to make sure they've obtained the correct binary for their machine. This promises to go a long way in making the transition to 64-bit Mac software very smooth and virtually invisible to most users.