A billion bytes, often shortened to gig in conversation. 1. Hard disks and flash drives measure computer storage in SI units, which are based on the base 10, or decimal, system, so GB is one billion (10 9 ) bytes, or 1,000,000,000 bytes. See also byte, decimal, and SI. 2. Internal computer memory is based on a base 2, or binary, number system.A GB of internal memory, therefore is 1,073,741,824 (2 30 ) bytes.The term GB comes from the fact that 1,073,741,824 is nominally 1,000,000,000. See also byte, G, and SI.