The evolution of the ATX power supply seems to be a constant process as computer hardware becomes more powerful and power hungry. First we had simple units with three basic +3.3V, +5V, and +12V rails, then came extra features like Power Factor Correction (PFC) to help deliver cleaner, more efficient power, then came the introduction of SATA hard drives and the PCI-Express interface spurring on the introduction of a new ATX 12v 2.0 standard.