The INT 04H vector can be used as one way to minimize the size of programs
that perform a lot of arithmetic operations.

After any arithmetic operation, the INTO instruction will test for
arithmetic overflow, and if the CPU flag is set (OF=OV=1), then INT 04H
is executed.

You might see code such as:

mov     ax,var_1
add     ax,var_2
into              ;2-byte test for arithmetic overflow
... etc. ...          ;either no overflow or it has been handled
; by the interrupt handler

See Also: INT 00H (division by 0)
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INT 04H: Overflow Interrupt