INT 04h (4)              Overflow
 
    Called when either an INTO (Interrupt on Overflow) instruction is
    encountered and the Overflow Flag (OF) is set, or when an INT 4
    instruction is encountered.
 
    This service gives programmers a way to provide a common handler for
    all arithmetic overflow conditions. By executing an INTO instruction
    after any arithmetic operation, a program can ensure that overflow
    conditions are properly handled.