This Hyperdrive fan photo shows how GCC mounted a cooling fan in one of the diagonal vents at the top-back of the Mac case (inside, of course). It pulls air up from the vents in the bottom of the case and out through that vent at top. Since hot air rises, this works well to cool the case. Other third party fans did basically the same thing, except they installed externally in the handle section of the case. I personally like the internal fan because you can't see it from the outside, so the machine looks stock. However, you can hear it though. But that was in an era before Silenx and other quiet fans.