INT 64 - Extended Batch Language v3.14+
        AH = function
            00h to 5Fh chained to previous handler
            60h to 6Ch reserved, return immediately
            80h to FFh chained to previous handler
            6Dh (v4.01+) insert tone in queue
                AL = ???
                CX = frequency in Hertz
                DL = duration in clock ticks
                Return: AL = 00h if note stored
                           = 01h if no room to store
            6Eh clear ??? counter/flag
            6Fh return counter/flag that AH=6Eh clears
            70h ???
                AL = ???
            71h ???
                AL = ???
            72h ???
            73h insert byte at end of keyboard buffer
                AL = byte to insert
                Return: AL = 00h if byte inserted
                           = 01h if no room to store
            74h insert byte at front of keyboard buffer
                AL = byte to insert
                Return: AL = 00h if byte inserted
                           = 01h if no room to store
            75h ???
            76h get keyboard "stack" status
                AL = 'K' if kbd read will read physical keyboard
                     'S' if it will read EBL internal keyboard buffer
                AH = ???
            77h clear internal keyboard buffer
            78h ???
                AL = ???
            79h ???
            7Ah ???
                AL = ???
            7Bh ???
                AL = ???
            7Ch ???
                AL = ???
            7Dh ???
                AL = ???
            7Eh clear buffer for ???
            7Fh installation check
                Return: CX = version in BCD
                        DI = segment of ???
                        BX = segment of next program's PSP???
Notes:  Extended Batch Language is a batch-file enhancer by Seaware
        the chaining does not check whether the interrupt had been hooked
          before, so if you try to chain when the previous vector was
          0000h:0000h, you'll be in trouble
        functions 72h and 7Ah-7Dh appear to be interfaces to the optional
          floating-point and extended function packages