INT 1B - BIOS Ctrl-Break Handler Address

	- holds address of the BIOS Ctrl-Break interrupt handler
	- called by INT 9 after Ctrl-Break key is pressed; INT 9 sets the
	  BIOS keyboard head and tail pointers to the buffer start and
	  places a zero word in the buffer
	- the BIOS initially sets this value to point to a simple IRET but
	  DOS re-vectors this to its own code, usually 2 lines of code that
	  sets an internal flag (to 3) and then returns via IRET.
	- DOS checks this flag on entry to many of its subfunctions.  If the
	  flag is set, it invokes INT 23.
	- pointing this address to a null function with and IRET disables
	  Ctrl-Break aborts
	- if the INT 1B code chooses to retain control of the system, it
	  must issue an EOI for any interrupt pending on the 8259 and reset
	  all I/O devices
	- should be terminated via an IRET
	- should not be called directly by user application