Data storage companies decided early on that all their products should be marketed in the decimal system. Our computers work on base 2 (binary) number system rather than the decimal system.
Therefore, one megabyte on their products is equal to 1,000,000 bytes, and one gigabyte is equal to 1,000,000,000 bytes. To a computer, however, a megabyte is 1,048,576 bytes and a gigabyte is 1,073,741,824 bytes.