Inconsistencies when making copies using different function

[amrcvth]

Is there a difference between the "restore data from an image" function and the "copy a disk to a disk" function? I created an image of my desktop's entire HDD and stored it onto an external hard drive (F:). Then I copied this image to another external hard drive (E:) using the "copy a disk to a disk" function. Both the external hard drives are identical--same manufacturer, same amount of storage space, same model. After copying the image onto (E:), both hard drives had the same amount of free space. Why is it that when I "restore data from an image" from (F:) to (E:) there is a discrepancy? (E:) has 3 more gigabytes of space taken up even though when looking at the properties of both (E:) and (F:) they have the same number of files.