INT 1bH: Keyboard Break

 This vector (0:006c) is taken by BIOS when it senses a press of the
 Ctrl-Break key.

 INT 1bH initially points to an IRET, but DOS sets it to point to local
 code that sets an internal DOS flag.  DOS tests every once in a while and
 acts upon it, depending upon the state of DOS break-testing.

 See DOS Fn 33H and INT 23H for descriptions of how DOS handles Ctrl-Break.

 A flag in the BIOS Data Area (0:0471) gets set upon the first occurrence
 of Ctrl-Break, but it never gets reset unless you do it yourself.  You
 might use this flag as a way to determine if a child process was aborted
 via Ctrl-Break.

See Also: DOS Interrupts
          ROM-BIOS Functions