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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)
Category: DOS Kernel - Int 21h - D
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