DMEDIUM_TOTAL [(#channel)] or
This function returns the number of total sectors available on the medium on which the specified file or directory is located, or to which the specified channel is open. If no parameter is specified, it looks to channel #3 (or #1 if #3 is not open).
DMEDIUM_FREE allows you to find out the number of sectors which currently do not contain any data on the related medium. DIR can also be used to obtain this information. FORMAT releases all sectors on a disk, marking any which may be corrupt as unavailable.