This led to the decision to split the components onto two separate circuit boards; one housing the CPU/GPU, memory, and power regulators, and a second board to act as a Southbridge board for slower input/output (I/O) functions. The boards mounted on opposite sides of an aluminum chassis helped to create air channels for cooling. The remaining components - the heat sink, the electric shielding, the power supply, the optical drive, and the cooling fan were then arranged in a Tetris-like fashion, according to principal designer Chris Kujawski, to achieve a compact form factor, resulting in the tower-like structure. To meet the acoustics factor, the system includes numerous sensors for controlling the speed of the fan, and the large open top was necessary to assure good air flow through the system. While certain elements like the optical drive, air flow requirements, and heat sink size fixed certain dimensions in the overall form factor, they were satisfied they were able to end up with a square footprint for the unit.