Function 25h            Set Interrupt Vector

    Replaces the vector-table entry with the address of the specified
    interrupt handler.

        Entry   AH    = 25h
                AL    = Interrupt number
                DS:DX = Address of interrupt handler

        Return  Nothing

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    Programs should never set an interrupt handler by directly
    manipulating the interrupt vector table.

    When a program installs a new interrupt handler, it should use
    function 35h to retrieve the address of the original interrupt
    handler and restore this original address before terminating.