INT 21,33 - Get/Set System Values (Ctl-Break/Boot Drive)

	AH = 33h
	AL = 00 to get Ctrl-Break checking flag
	   = 01 to set Ctrl-Break checking flag
	   = 02 to set extended Ctrl-Break checking
	   = 05 get boot drive (DOS 4.x)
	DL = 00 to set Ctrl-Break checking off
	   = 01 to set Ctrl-Break checking on
	   = boot drive for subfunction 5;  (1=A:, 2=B:, ...)


	on return:
	DL = 00 Ctrl-Break checking OFF (AL=0 or AL=2)
	   = 01 Ctrl-Break checking ON	(AL=0 or AL=2)
	   = boot drive number (1-26, A: - Z:) (function 05)


	- retrieves DOS Ctrl-Break or extended Ctrl-Break setting which
	  determines if DOS will check for Ctrl-Break during INT 21 calls