The Drive Used pushbutton is labeled to indicate the contents of the drive Used window immediately below it. The windowed data are the allocated bytes used on the drive of the active file window.
When pushed, the data window will show the allocated bytes
used
on all local fixed drives.
Dropping a color or font in this button from one of the system palettes will propagate the color or font thoughout the other buttons in the Data Panel.

Total
Local Fixed Disk Space