A method for operating a graphical user interface of a computer terminal running multiple asynchronous simultaneous tasks. The porous metal layer is made of nickel or silver and has a density ratio of 50 to 90%. The serial channels are convertible into one or more time division multiplexed channels. A filter cartridge arrangement is described and shown. A calculation of the polarity inversion is performed in accordance with the polarity inversion instruction, whereby waveform data corresponding to one period of sinusoidal wave can be simply generated.