<P> When Intel developed the ATX standard power supply connector (published in 1995), microchips operating on 3.3 V were becoming more popular, beginning with the Intel 80486DX4 microprocessor in 1994, and the ATX standard supplies three positive rails: + 3.3 V, + 5 V, and + 12 V. Earlier computers requiring 3.3 V typically derived that from a simple but inefficient linear regulator connected to the + 5 V rail . </P> <P> The ATX connector provides multiple wires and power connections for the 3.3 V supply, because it is most sensitive to voltage drop in the supply connections . Another ATX addition was the + 5 V SB (standby) rail for providing a small amount of standby power, even when the computer was nominally "off". </P> <P> There are two basic differences between AT and ATX power supplies: the connectors that provide power to the motherboard, and the soft switch . In ATX - style systems, the front - panel power switch provides only a control signal to the power supply and does not switch the mains AC voltage . This low - voltage control allows other hardware or software to turn the system on and off . </P> <P> As transistors become smaller on chips, it becomes preferable to operate them on lower supply voltages, and the lowest supply voltage is often desired by the densest chip, the central processing unit . In order to supply large amounts of low - voltage power to the Pentium and subsequent microprocessors, a special power supply, the voltage regulator module began to be included on motherboards . Newer processors require up to 100 A at 2 V or less, which is impractical to deliver from off - board power supplies . </P>

What is the difference between at and atx power supply
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