Actually, 1 gigabyte (10^9^ B) is 1000 megabytes (10^6^ B), while one gibibyte (2^30^ B) corresponds to 1024 mebibytes (2^20^ B). I know that in some circles, 1 GB is treated as 1 GiB, so I don’t blame you. This system of quantities is standardised internationally in order to conform with the SI (mega must mean a million times and not 2^20^ times), but many don’t conform to it, such as Microsoft as far as I know.