Int 21H, AH=36H

2 and higher

GET FREE DISK SPACE

DosQFSInfo

      AH = 36h
      DL = drive number (00h = default, 01h = A:, etc)

AX = FFFFh if invalid drive

      else
          AX = sectors per cluster
          BX = number of free clusters
          CX = bytes per sector
          DX = total clusters on drive

free space on drive in bytes is AX * BX * CX

total space on drive in bytes is AX * CX * DX

“lost clusters” are considered to be in use

according to Dave Williams' MS-DOS reference, the value in DX is incorrect for non-default drives after ASSIGN is run

this function does not return proper results on CD-ROMs; use AX=4402h“CD-ROM” instead

(FAT32 drive) the reported total and free space are limited to 2G-32K should they exceed that value

AH=1Bh,AH=1Ch,AX=4402h“CD-ROM”,AX=7303h

Text based on Ralf Brown Interrupt List Release 61