all hard drives have a loss factor of gigabytes
this is taking up by file alocation tables (FAT) and information needed for the OS to recognise the drive.

my 1tb only reads 931gb (ripped!!)

also read here - http://en.wikipedia.org/wiki/Gigabyte

Your hard drive is advertised as having a 60GB capacity, but your computer shows only 55.8GB. What gives? The discrepancy is the result of having two methods of measuring memory. Computers are binary, or "base two," mathematical systems, and in a binary world a kilobyte is 1024 bytes (2 to the 10th power). When computers were new, the geekerati referred to this as a "kilo." Noncomputer folks, however, understood kilo to mean thousand, and thought that 1000 bytes should equal a kilobyte. So, two different measurements of hard drive space were born. In 1998, the International Electrotechnical Commission (IEC) weighed in, defining 1 "gigabyte" as 1 billion bytes. Hard disk manufacturers agree, marketing their products using the rounder decimal value instead of the binary system. So, your drive is labeled as decimal ("giga") and your PC reads binary (IEC's term, "gibi"). Either way, you're getting the same bunch of bytes