INT 21 - DOS 2+ - IOCTL - 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
Return: CF clear if successful
AX = number of bytes actually read
CF set on error
AX = error code (01h,05h,06h,0Dh) (see AH=59h)
Note:   format of data is driver-specific
SeeAlso: AX=4405h,INT 2F/AX=122Bh

See also: 214402

214404 - DOS 2+ - IOCTL - READ FROM BLOCK DEVICE CONTROL CHANNEL