Because of the G4 Cube's small size, Apple was forced to "think outside the box" -- literally. There isn't enough room to put everything inside. The Cube's external power supply, for example, takes up about as much room as a three-egg omelette, a fact Apple didn't bother to publicize.
Also completely external is the Cube's sound output.
The G4 Cube comes with a pair of crystal-clear, eyeball-shaped speakers created by Harman Kardon and Apple. They belt out 20 fair-sounding watts of sonic force between the frequencies of 80Hz and 20kHz, all through the power of the Cube's USB port. How? Because of the efficiency of the digital amplifier housed in a box along the USB cable. The amp even has an analog headphone jack -- good news since the Cube itself has no I/O for speakers or microphones, other than USB.
"This is at the heart of Apple. We want Apple to stand at the intersection of art and technology."
-- Apple CEO Steve Jobs on iMovie 2