Jim found a duplicate file on a backup hard drive and wants to know how he can find other duplicates. Is there an app for that? Leo says that a program that can prevent duplications when backing up is SuperDuper by Shirt Pocket Software. Jim can set it up to mirror his internal drive and then if the internal drive dies, he can boot up from the external drive. Gemini Duplicate File Finder will do the job for the Mac, and it's $20 to buy. But be sure they're looking inside the file to verify it's a duplicate!