Format of DOS device driver header: Offset Size Description ) 00h DWORD pointer to next driver, offset=FFFFh if last driver 04h WORD device attributes (see #01647,#01648) 06h WORD device strategy entry point call with ES:BX -> request header (see #02597 at INT 2F/AX=0802h) 08h WORD device interrupt entry point ---character device--- 0Ah 8 BYTEs blank-padded character device name ---block device--- 0Ah BYTE number of subunits (drives) supported by driver 0Bh 7 BYTEs normally unused; sometimes contains signature to indicate specific drivers: "$PCMATA" PCMCIA driver PCMATA.SYS (see AX=440Dh"DOS 3.2+") "AHADDVR" Adaptec SCSI disk driver ASPIDISK.SYS "DBLSPAC" MS DoubleSpace or DriveSpace "DSKREET" NortonUtils v5+ Diskreet (see INT 2F/AX=FE00h) "GFS " LapLink III device driver DD.BIN "SIDExxx" PCMCIA driver ATADRV.EXE (see AX=440Dh"DOS 3.2+") "STAC-CD" Stacker/Stacker Anywhere (see AX=4404h"Stacker") ---DoubleSpace/DriveSpace--- 12h 2 BYTEs signature ",." (2Ch 2Eh) 14h var preloading API entry point ---CD-ROM--- 12h WORD reserved, must be 0000h appears to be another device chain 14h BYTE drive letter, 01h=A:, etc. (must initially be 00h; this byte is set by MSCDEX when it loads) 15h BYTE number of units 16h 6 BYTEs signature 'MSCDnn' where 'nn' is version (currently '00') (this field does not exist in most drivers) SeeAlso: #02550 at INT 25/AX=CDCDh,#02845 at INT 2F/AX=5600h