The device-close function is supported only under MS-DOS versions 3.0 and later and is called only if bit 11 is set in the device attribute word of the device header.
On block devices, this function can be used to manage local buffering and to decrement a reference count of the number of open files on the device; when the count reaches zero, all files have been closed and the driver should flush buffers because the user may change disks.
On character devices, the device-close function can be used to send a device-dependent post-I/O string such as a formfeed. (This string can be set into the driver by an application program by means of an IOCTL write function.) Note that the predefined handles for the CON, PRN, and AUX devices are never closed.
The device-close function is called with
RH + 1 BYTE Unit code (block devices)
RH + 2 BYTE Command code = 14 (0EH)
It returns
RH + 3 WORD Status