About these units
gigabyte (GB)
A gigabyte (GB) is one billion bytes. Drive makers use decimal GB while Windows shows binary values (GiB) labeled GB, which is why a 1 TB drive shows about 931 GB.
megabyte (MB)
A megabyte (MB) is 1,000,000 bytes. Some operating systems show mebibytes (1,048,576 bytes) labeled MB, so the same file can appear with slightly different sizes.