This article explains how to position the Power Mac G4 Cube computer so that is adequately cooled during normal use.

The Power Mac G4 Cube computer does not have a cooling fan. Heat generated by the computer--a normal part of its operation-- escapes through cooling vents. To provide adequate cooling for the computer's internal components, it must be positioned vertically with the DVD disc drive facing up.

Do not place anything on top of the computer that would prevent its normal ventilation.