The Infamous Powermac G4 Cube, apple's original failed attempt at a compact G4-Based Macintosh. Released in 2000 at a cost of $1599, the cube was considered too expensive, and too slow. The Cube Unlike many other computer's uses passive cooling, where there is no fan. This was a big mistake on apple's part, because G4 processors run very hot!
The Cube boasted a 450MHz or 500Mhz G4 CPU, not very fast, back then, they had 1Ghz Pentium III's The cube is virtually silent, except for the original 5400 RPM hard drives, After one year of production, Apple put the cube "On Ice." The Cube is also a popular candidate for macquariums, it also has an internal fan hookup, but it isn't used by Apple. If you want, you can buy a fan, and connect it to the 12V 2-Pin connector, and find somewhere to put it in the cube, this is a popular mod to cool overheating cubes.
It was replaced by the Mac Mini in 2005, 5 years later. At a later time, I will re-post this as a repair guide.