Category: DOS kernel
INT 21 - DOS 1+ - GET ALLOCATION INFORMATION FOR SPECIFIC DRIVE AH = 1Ch DL = drive (00h = default, 01h = A:, etc) Return: AL = sectors per cluster (allocation unit), or FFh if invalid drive CX = bytes per sector DX = total number of clusters DS:BX -> media ID byte (see #01356) Notes: under DOS 1.x, DS:BX points at an actual copy of the FAT; later versions return a pointer to a copy of the FAT's ID byte on a DBLSPACE drive, the total number of clusters is based on the estimated compression ratio this function may not be properly supported on CD-ROMs and other installable file systems (use AX=4402h"CD-ROM" for CD-ROMs instead) BUG: DOS 7.10 (Win95B/Win98) reportedly returns incorrect values in AL and DX for FAT12/FAT16 drives, even though it manages correct results for FAT32 drives (DOS windows are not affected, only real-mode DOS) SeeAlso: AH=1Bh,AH=36h