INT 13 - HARD DISK - READ SECTOR BUFFER (XT only)
        AH = 0Eh
        DL = drive number (80h = first, 81h = second hard disk)
        ES:BX -> buffer
Return: CF set on error
        CF clear if successful
        AH = status code (see AH=01h)
Notes:  transfers controller's sector buffer.  No data is read from the drive
        used for diagnostics only on PS/2 systems