sagra

Can someone please tell me how I can see what files are on one drive and not on a second drive, regardless of what folders the files are in? In other words I want to know what files are anywhere on one drive and that are not anywhere on the second drive....and I need to be able to move those files to the second drive. So far any program I have found will only compare by folder and not by the whole drives in general. Anyone's help with this would be most appreciated. This seems like a function that many people would want, so they could have at least one copy of every file they own (that are spread across multiple external drives) all on one large drive for the sake of archiving. I am using Windows 7. computer is an HP with an AMD Athlon II quad core 630 processor. Thanks in advance for any help. Bob