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In recent years the "digital home" has created a need for many electronic home appliances. Some of them are redesigned from PCs and have made the physical PC invisible everywhere in our living environment. Thus "System standby all the time" has become an important feature for turning on a PC instantly. In this paper we use the "Suspended to RAM" method to replace the "System off method to perform an instantaneous turning-on just like some other consumer electronics have done, and we redesign the circuit to reduce the standby power consumption of a PC. First, we use CMOS as the current switch, thus avoiding the static current consumption between chips or modules, and we turn off the USB, PS/2 and network controller power supply with the USB, PS/2 and LAN waking-up function disabled. Second, we turn off the power supply for the termination resistor of the memory modules. Third, we use the high-efficiency pulse width modulation power regulator to replace the linear power regulator. Fourth, we enlarge the value of the divider resistors for the reference voltage to reduce the leakage current. Overall, these improvements reduce the standby power consumption from 2.4 watts to 0.7 watt. In addition, our design shows that the PC can be turned on within 3 seconds by reloading the OS in the DRAM.