^^^ second that, i mean whats really worht backing up anyways, music,vidoes,games,doc's, bookmarks and...porn a few simple fodler for most copy and paste or drag and drop no fuss no muss
The software will take an image of the hard disk. This means that the bits will be copied exactly even if they are not used so that everything is in the same place as it would be on the old disk.
Either that or as you might know, when you delete something on windows it won't physicaly delete it until the file is overwritten, so if you havent "reclaimed" that space of the disk then it still has data on it (all-be-it hidden) so this area of the disk is included in the image.