How is "craft()->fileCache" different from using cookies?
Correct... craft()-&gt;fileCache will save to your craft/storage/runtime/cache folder by default, which will have a .bin file that has a hash of the key you provided when calling set() and the contents will be a serialized version of the value you passed in.

Also worth noting that while craft()-&gt;fileCache still exists, as of Craft 2.0, it is simply a shortcut to craft()-&gt;cache, when the cacheMethod config setting is set to file.