INT 21,44,F / IOCTL,F - Set Logical Drive

	AH = 44h
	AL = 0F
	BL = new drive number (0=default, 1=A:, 2=B:, 3=C:, ...)

	on return
	AX = error code if CF set  (see DOS ERROR CODES)
	AL = logical drive number (should be equal to BL input)
	   = 0 if drive accessed by only one drive specifier
	   = 1 if drive A:, 2 if drive B:, etc

	- changes the logical drive designator of the physical drive
	  to be accessed next
	- implemented from DOS 3.2