In a nutshell, desktop computer operating systems (Mac, Windows, and Linux) are in transition from 32 bit to 64 bit so that computer hardware can support more than 4 GB of Random Access Memory (RAM).
For Mac OS X, the transitionary version of the OS happens to be Mac OS X 10.7. This means that as of Mac OS X 10.7 there is still support for 32-bit Apps and 32-bit System Preferences (that is, those that are limited to 4 GB of memory) but that Apple want developers to switch to 64-bit Apps and System Preferences because future versions of Mac OS X will not support the 32-bit versions.
While many developers need to go through a transition, because they have existing program code or because they want to continue to support older 32-bit systems for some time to come, we are not going to consider the 32-bit issue (other than this mention of it) so everything that we develop will be 64 bit.
We need to be aware of this because it is possible that if we try to share...