INT 21,44,5 / IOCTL,5 - Write to Block Device

AH = 44h

AL = 05

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

CX = number of bytes to send

DS:DX = pointer to data buffer

on return

AX = number of bytes written if CF clear

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

- block devices are not required to support this function

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