Int 2F Fn 4A11  - Dblspace.bin - "getdrivespace" - Get Space Avail On Com  [d]

   AX = 4A11h
   BX = 0007h
   DL = compressed drive number (0=A:)

Return: AX = status (0000h,0102h) (see also AX=4A11h/BX=0001h)
       0000h successful
       DS:SI -> free space record (see below)
Program: DBLSPACE.BIN is the resident driver for DoubleSpace, the
     disk-compression software bundled with MS-DOS 6.0

See Also: AX=4A11h/BX=0000h,AX=4A11h/BX=0008h

Format of free space record:
Offset Size    Description
 00h   DWORD   total number of sectors in drive's sector heap
 04h   DWORD   number of free sectors in drive's sector heap