INT 03h (3)              Breakpoint

    INT 3 is the breakpoint interrupt.

    Debuggers use this interrupt to establish breakpoints in a program
    that is being debugged.  This is normally done by substituting an INT
    3 instruction, which is one byte long, for a byte in the actual
    program.  The original byte from the program is restored by the
    debugger after it receives control through INT 3.