Base 10 format #
Disk space is always shown as base 10 in iStat Menus. Hard drive manufacturers usually quote the size of their HDs as base 10, where 1 GB equals 1,000,000,000 bytes. Some operating systems show disk space as base 2, where 1 GB equals 1,073,741,824 bytes. However, since Snow Leopard, macOS shows disk space as base 10.
iStat Menus 4 uses base 10 format for all disk storage figures.
A note about free space #
If you’re using Time Machine, and if your Time Machine drive isn’t connected, macOS 10.7 Lion creates local backups on your startup volume. The Finder doesn’t report this space as used, but Disk Utility and iStat Menus do. For more information, please read this article by Roberto Valerio.
That’s why the Finder and iStat Menus show a different value for drive free space.