INT 13 - XDF.COM - API(Application Program[ming] Interface) The defined set of calls which a program may make to interact with or request services of the operating system or environment under which it is running.  Because the inputs and outputs of the calls are well-defined, a program using the API can continue using the identical calls even if the internal organization of the program providing the API changes.
	AH = 18h
	CX = D2C9h ("R"+80h, "I"+80h = Roger Ivey)
	DX = 0000h
	BX = function
	    0000h installation check
		  Return: AH = 0Ch
			  CX = 7269h ("ri" = Roger Ivey)
			  ES = segment of driver
			  CF set
	    2F64h ("/d") disable the driver
		  Return: AH = 0Ch
			  ES:BX = pointer to activation flag (it is set to 0:
				  set it to 1 to enable the driver again)
			  CX = 7269h
			  CF set
	    2F75h ("/u") unload the driver (restore interrupts & free memory)
		  Return: AH = 0Ch
			  DL = 55h ("U") if successful
			     = 00h	   if fails
			  CX = 7269h
			  ES = segment of driver
			  CF set
			  AL, BX, DH, and DI destroyed
Program: XDF is a TSR(Terminate and Stay Resident) A program which remains in memory after terminating in order to provide services to other programs or the user.  The name comes from the name of the DOS function call used to remain in memory after termination. provided with PC-DOS 7.0 to support XDF 1.84M disks,
	  developed by Roger D. Ivey
Note:	After disabling or enabling the driver, a disk change must be performed
	  or simulated to reset the driver.