That is the only one you *need* per se but it doesn't
hurt having extra ventilation esp if you put other
hot running boards in there ( gfx cards for example )
It is a shame that we are now so far removed from the quiet computer - like the Spectrum, Sam Coupe, Amiga500 etc.
Hard drive noise, fan noise and CPU fan noise are
all doing their bit to make the computer the noise generating monstrousity of our age.
