{{page>en:templates:dosint}} ====== Int 21H, AH=1BH ====== ===== Version ===== 1 and higher ===== Brief ===== GET ALLOCATION INFORMATION FOR DEFAULT DRIVE ===== Family API ===== none ===== Input ===== AH = 1Bh ===== Return ===== AL = sectors per cluster (allocation unit) 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 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) Values for media ID byte: FFh floppy, double-sided, 8 sectors per track (320K) FEh floppy, single-sided, 8 sectors per track (160K) FDh floppy, double-sided, 9 sectors per track (360K) FCh floppy, single-sided, 9 sectors per track (180K) FAh HP 200LX D: ROM disk, 16 sectors per track (995K) HP 200LX E: (Stacker host drive ???) F9h floppy, double-sided, 15 sectors per track (1.2M) floppy, double-sided, 9 sectors per track (720K,3.5") F8h hard disk F0h other media (e.g. floppy, double-sized, 18 sectors per track -- 1.44M,3.5") ===== See also ===== AH=1Ch,AH=36h ===== Note ===== Text based on [[http://www.cs.cmu.edu/~ralf/files.html|Ralf Brown Interrupt List Release 61]] {{page>en:templates:int}} {{page>en:templates:fapi}}