This page gives various information about the current drive, as given by
DOS.

  Logical drives are both real drives, and those created by the SUBST
command.

  For the current drive, the drive type may not always be correct. There is
no standard way of telling if a drive is actually a ramdisk or similar.
  A door lock is used by high density drives to let DOS know if a floppy
has been removed.
  A cluster is what DOS uses to keep track of data on the disk. A cluster
consists of several actual sectors of data. A standard hard disk will have
4 sectors in each cluster (2K of data.)