Int 21H, AH=44H, AL=04H

2 and higher

READ FROM BLOCK DEVICE CONTROL CHANNEL

AX = 4404h
BL = drive number (00h = default, 01h = A:, etc.)
CX = number of bytes to read
DS:DX -> buffer

CF clear if successful

    AX = number of bytes actually read
CF set on error
    AX = error code (01h,05h,06h,0Dh) (see #01680 at AH=59h/BX=0000h)

format of data is driver-specific
this function was not supported by Digital Research's DOS Plus

AX=4402h“DOS 2+”,AX=4405h“DOS”,INT 2F/AX=122Bh

Text based on Ralf Brown Interrupt List Release 61