<Li> Because of the DC - DC converters on the motherboard that convert 12 V to the low voltages required by the Intel Pentium 4 and AMD Athlon XP (and subsequent) processors, such systems draw most of their power from the 12 V rail . </Li> <Li> Original ATX PSUs have power distribution designed for pre-P4 / XP PCs . They lack the supplemental 4 - pin 12 - volt CPU power connector, so they most likely cannot be used with P4 / XP or newer motherboards . Adapters do exist but power drain on the 12 V rail must be checked very carefully . There is a chance it can work without connecting the 4 - pin 12 V connector, but caution is advised . </Li> <Li> ATX12V 1. x PSUs have power distribution designed for P4 / XP PCs, but they are also greatly suitable for older PCs, since they give plenty of power (relative to old PCs' needs) both on 12 V and on 5 V / 3.3 V. It is not recommended to use ATX12V 1. x PSUs on ATX12V 2. x motherboards because those systems require much more power on 12 V than ATX12V 1. x PSUs provide . </Li> <Li> ATX12V 2. x PSUs have power distribution designed for late P4 / XP PCs and for Athlon 64 and Core Duo PCs . They can be used with earlier P4 / XP PCs, but the power distribution will be significantly suboptimal, so a more powerful ATX12V 2.0 PSU should be used to compensate for that discrepancy . ATX12V 2. x PSUs can also be used with pre-P4 / XP systems, but the power distribution will be greatly suboptimal (12 V rails will be mostly unused, while the 3.3 V / 5 V rails will be overloaded), so this is not recommended . </Li>

How does the atx form cool the motherboard