Transfer of files

Have a customer asked me this question: Had another tech look at his computer today:

 I have a document (a folder) on the Dell 6000 which is  7.05 MB.  I copied it to a flash drive and Duane inserted into the XPS, but  when you "hang the arrow" over it (Duane's terminology) it shows only 6.61 MB, but when you right click on "properties" it shows 7.05.  What's the  deal.
Has the entire 7.05 document really been transferred  correctly?

This gets even stranger.  When I inserted the 7.05 MB document into my  new 5000 at home, the hanging arrow shows only 6.59 MB, and properties shows only 7.03 MB.  What's going on?  Is all the information being  transferred?

Any explaination on this?