INT 21 - DOS 2+ - IOCTL - WRITE TO CHARACTER DEVICE CONTROL CHANNEL             
	AX = 4403h
	BX = file handle referencing character device
	CX = number of bytes to write
	DS:DX -> data to write
Return: CF clear if successful
	    AX = number of bytes actually written
	CF set on error
	    AX = error code (01h,05h,06h,0Dh) (see #01680 at AH=59h/BX=0000h)
Notes:	format of data is driver-specific
	  (also see separate entries below for some specific cases)
	if the file handle refers to "4DOSSTAK", the 4DOS (v2.x-3.03)
	  KEYSTACK.SYS driver will push the specified characters on the
	  keyboard stack; similarly for "NDOSSTAK", the NDOS KEYSTACK.SYS
	  driver will push the characters onto the keyboard stack
	this function was not supported by Digital Research's DOS Plus
SeeAlso: AX=4400h,AX=4402h"DOS 2+",AX=4405h"DOS",INT 2F/AX=122Bh
SeeAlso: INT 2F/AX=D44Dh,INT 2F/AX=D44Fh
                                                                                

INT 21 U - MS-DOS 7.0+ - CONFIG$ device - SET??? CONFIGURATION INFORMATION      
	AX = 4403h
	BX = file handle for character device "CONFIG$"
	CX = number of bytes to write
	DS:DX -> buffer containing ???
Return: CF clear if successful
	    AX = number of bytes actually written
	CF set on error
	    AX = error code (01h,05h,06h,0Dh) (see #01680 at AH=59h/BX=0000h)
Note:	IOCTL Output to CONFIG$ is only available while IO.SYS is booting
	  the system; once CONFIG.SYS has been processed, this call always
	  succeeds, ignoring any input
SeeAlso: AX=4403h"CONFIG$"