I have mp3 files that I want to move from cdrive to backup on usb connected drive but I need to know how much space I need for this. When I look at other files in a folder, I see at the bottom the total size of all the files I select. But when I do that with mp3 files it doesn't show me the total size. It shows only the total time length of the files. What am I doing wrong that it doesn't show me the total size of mp3 files?