<br>From Macworld.com:<br><br><br>"Inside the iMac's base is a custom-designed circular motherboard, featuring a bus speed of 100MHz. Also aboard is a cooling fan, made necessary by the iMac's dense engineering and the heat of the high-speed G4 processor. However, Apple says the fan's as quiet as a whisper during normal use. In addition, the fan's intelligent enough to only crank up to full speed when it's really warm inside."<br><br>