Offset Size Description 00h DWORD pointer to next driver, offset=FFFFh if last driver 04h WORD device attributes Character device: bit 15 set bit 14 IOCTL supported (see AH=44h) bit 13 output until busy supported bit 12 reserved bit 11 OPEN/CLOSE/RemMedia calls supported bits 10-7 reserved bit 6 Generic IOCTL call supported (command 13h) (see AX=440Ch,440Dh) bit 5 reserved bit 4 device is special (use INT 29 "fast console output") bit 3 device is CLOCK$ bit 2 device is NUL bit 1 device is standard output bit 0 device is standard input Block device: bit 15 clear bit 14 IOCTL supported bit 13 non-IBM format bit 12 reserved bit 11 OPEN/CLOSE/RemMedia calls supported bit 10 reserved bit 9 ??? set by DOS 3.3 DRIVER.SYS for "new" drives bit 8 ??? set by DOS 3.3 DRIVER.SYS for "new" drives bit 7 reserved bit 6 Generic IOCTL call supported (command 13h) implies support for commands 17h and 18h (see AX=440Ch,440Dh,440Eh,440Fh) bits 5-2 reserved bit 1 driver supports 32-bit sector addressing bit 0 reserved 06h WORD device strategy entry point call with ES:BX -> request header (see INT 2F/AX=1510h) 08h WORD device interrupt entry point 0Ah 8 BYTEs blank-padded character device name 12h WORD (CD-ROM driver) reserved, must be 0000h 14h BYTE (CD-ROM driver) drive letter (must initially be 00h) 15h BYTE (CD-ROM driver) number of units 16h 6 BYTEs (CD-ROM driver) signature 'MSCDnn' where 'nn' is version (currently '00')