Windows is using the unit "Gigabytes" instead of "Gibibytes", which is wrong and confuses people.
1 Gigabyte is 1 000 000 000 bytes, and 1 Gibibyte is 1 073 741 824 bytes. However, Windows states that 1 073 741 824 bytes is 1 Gigabyte.
So, if I create a 30 GiB partition using whichever OEM setup tool, Windows will display it as 32 243 707 904 bytes, or 30 GB in Windows Explorer. This is wrong. It should say 30 GiB or 32,2 GB.
If the OEM setup tool also wrongly uses GB instead of GiB, a 30 "GB" created partition will end up displaying as 29,99 GB in Windows Explorer.
To add to the confusion, Disk Management reports a 30 GiB partition as 30,03 GB.
More information:
http://en.wikipedia.org/wiki/SI_prefix#Computing
Of course, this also applies to MB and TB in Windows.
