I'd just like to interject for moment. What you're refering to as gigabyte, is in fact, gibibyte, or as I've recently taken to calling it, gibi * byte. Giga does not become a binary prefix when used with byte, but rather remains a decimal one.

Many computer users count gibibytes every day, without realizing it. Through a peculiar turn of events, the unit with gibi prefix which is widely used today is often called gigabyte, and many of its users are not aware that it is basically a gibi prefixed unit, approved by IEC.