Santa and Banta are employed in a computer

Santa and Banta are employed in a computer hardware store as movers.
One day both of them are asked to move some computers. Santa being energetic that day does
not feel the computer to be heavy at all.
At the same time he sees that Banta is struggling very hard to lift his computer.
At this Santa says, "What Banta, my computer has 500 MB Hard Disk yours has just 250, even
then you cannot lift it?"
At this Banta thinks for a while and replies "That is right, but my Hard Disk is full and
yours is empty"