INT 21,44,4 / IOCTL,4 - Read from Block Device

AH = 44h

AL = 04

BL = drive number (0=default, 1=A:, 2=B:, 3=C:, ...)

CX = number of bytes to read

DS:DX = pointer to data buffer

on return

AX = number of bytes read if CF clear

= error code if CF set (see ~DOS ERROR CODES~)

- block drivers are not required to support this function

- returns AX = 01 (invalid function code) if not supported