Action: Provides a direct link into the XIOS to allow data to be written from a specified memory location to disc, starting at a specified logical disc sector.

On entry: AL = Drive number (0 = A:, 1 = B: etc)
CX = number of sectors to write
DX = start sector relative (logical) number
DS:BX = Segment offset of DTA

Returns: Carry clear if successful
Carry set if failed, AX = Error code, as shown for INT 25h.

Notes: See INT 25h. All comments apply.