We are all familiar with the behavior of a desktop PC running Windows XP with respect to applying power to and shutting down the system. Modern desktop PCs use an ATX compatible power supply which applies intelligence to the power-on/off behavior. These systems have essentially two power control switches. The power supply itself has a master switch that controls whether the power supply itself is on or off. Yet the power supply can also be controlled with software. When you execute a shut-down from Windows XP, the operating system sends a command to the power supply to shut off. The power supply’s power switch remains in the on-position. The system is then turned back on by pressing a “power-on” button, usually on the
front of the system. Pressing the power button tells the system to send a command to the power supply to turn on and the system boots.