The GB thing is a little tricky to me. This is how i understand it. A computer 1GB seems to be larger than a "actual" 1GB. (Like 2GB of ram in my PC is actually 2.095 GB of ram.) I think the 120 GB HDD is referring to "actual" GB while 113 GB is in reference to the computer oversize GB.
P.S I see someone else above explain it better than I have.







