Note: This API call is for DOS and Win16 personality only. Use Family API for portability.

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”)

AH=1Ch,AH=36h

Note

Text based on Ralf Brown Interrupt List Release 61

DOS API
Process manager	INT 20H, INT 21H: 00H, 25H, 26H, 31H, 34H, 35H, 4BH, 4CH, 4DH, 50H, 51H, 52H, 55H, 62H, INT 22H, INT 27H, INT 28H
File manager	INT 25H, INT 26H, INT 21H: 0DH, 0EH, 0FH, 10H, 11H, 12H, 13H, 14H, 15H, 16H, 17H, 19H, 1AH, 1BH, 1CH, 21H, 22H, 23H, 24H, 27H, 28H, 29H, 2EH, 2FH, 32H, 3305H, 36H, 39H, 3AH, 3BH, 3CH, 3DH, 3EH, 3FH, 40H, 41H, 42H, 4300H, 4301H, 45H, 45H, 46H, 4EH, 4FH, 54H, 56H, 5700H, 5701H, 5AH, 5BH, 5c00H, 5c01H, 60H, 67H, 68H, 6900H, 6901H, 6AH, 6CH
Character Device I/O	INT 29H, INT 21H: 01H, 02H, 03H, 04H, 05H, 06H, 07H, 08H, 09H, 0AH, 0BH, 0AH, 0CH, 5D07H, 5D08H, 5D09H, 5D0AH
Signals	INT 23H, INT 24H, INT 21H: 3300H, 3301H, 3302H
Memory manager	INT 21H: 48H, 49H, 4AH, 5800H, 5801H, 5802H, 5803H
Date and Time	INT 21H: 2AH, 2BH, 2CH, 2DH
Misc	INT 21H: 30H, 3306H, 3700H, 3701H, 3702H, 3703H, 59H
NLS	INT 21H: 3303H, 3304H, 3800H, 3801H, 6300H, 6301H, 6301H, 6500H, 6501H, 6502H, 6503H, 6504H, 6505H, 6506H, 6507H, 6520H, 6521H, 6522H, 6523H, 65A0H, 65A1H, 65A2H, 6601H, 6602H
Devices	INT 21H: 4400H, 4401H, 4402H, 4403H, 4404H, 4405H, 4406H, 4407H, 4408H, 4409H, 440AH, 440BH, 440CH, 440DH, 440EH, 440FH, 4410H, 4411H, 53H
Network	INT 21H: 5E00H, 5E01H, 5E02H, 5E03H, 5E04H, 5E05H, 5F00H, 5F01H, 5F02H, 5F03H, 5F04H, 5F05H, 5F07H, 5F08H
osFree Macro Library
Video I/O	@SetMode @SetCurSz @SetCurPos @GetCur @SetPage @ScrollUp @ScrollDn @Scroll @GetChAtr @PutChAtr @PutCh @SetPalet @SetColor @SetDot @GetDot @WrtTTY @VideoState @GetMode @GetDisplay @GetVideoState @GetEGAInfo @Cls
Hardware info	@Equipment @MemSize
Serial I/O	@AuxInit @AuxSendChar @AuxRecieveChar @AuxStatus
Tape I/O	@TapeOn @TapeOff @TapeRead @TapeWrite
Keyboard I/O	@KbdStatus @CharIn @CharPeek
Printer I/O	@PrnPrint @PrnInit @PrnStatus
Disk I/O	@DskReset @DskStatus @DskRead @DskWrite @DskVerify @DskFormat
Date and Time	@SetTime @GetTime
Mouse	@MouInit @MouShowPointer @MouStatus @MouSetPos @MouSetMickey @MouRegion
Memory manager	@ModBlok SET_BLOCK
Family API
DOS	Process Manager	DosBeep DosExit DosSleep DosExecPgm
File Manager	DosChDir DosChgFilePtr DosClose DosDelete DosDupHandle DosMkDir DosMove DosQCurDir DosQCurDisk DosSetFileMode DosOpen DosQFileInfo DosRead DosQFileMode DosQFSInfo DosQVerify DosRmDir DosSelectDisk DosFindClose DosFindFirst DosFindNext DosSetFileInfo DosSetVerify DosWrite DosFileLocks DosSetFHandState DosNewSize DosBufReset DosQFHandState DosSetFSinfo DosShutdown
Memory Manager	DosFreeSeg DosSubAlloc DosSubFree DosSubSet DosAllocHuge DosAllocSeg DosReallocHuge DosReallocSeg DosGetHugeShift DosCreateCSAlias
NLS	DosCaseMap DosGetCtryInfo DosGetDBCSEv DosSetCtryCode DosGetCollate DosGetMessage DosInsMessage DosPutMessage
Date and Time	DosSetDateTime DosGetDateTime
Devices	DosDevConfig DosDevIOCtl DosDevIOCtl2
Signals	DosHoldSignal DosSetSigHandler
Misc	BadDynLink DosGetEnv DosGetMachineMode DosGetVersion DosError DosErrClass DosSetVec
KBD	KbdCharIn KbdFlushBuffer KbdGetStatus KbdSetStatus KbdStringIn KbdPeek
VIO	VioGetBuf VioGetConfig VioGetCurPos VioGetCurType VioGetPhysBuf VioReadCellStr VioReadCharStr VioScrollUp VioScrollDn VioScrollLf VioScrollRt VioScrUnLock VioSetCurPos VioSetCurType VioSetMode VioGetMode VioShowBuf VioWrtCellStr VioWrtCharStr VioWrtCharStrAtt VioWrtNAttr VioWrtNCell VioWrtNChar VioWrtTTY VioScrLock VioPopUp
Tools	BIND
Modules	DOSCALLS.DLL VIOCALLS.DLL KBDCALLS.DLL MSG.DLL
Libraries	API.LIB OS2386.LIB FAPI.LIB DOSCALLS.LIB SUBCALLS.LIB