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CompTIA A+ Certification All-in-One Exam Guide

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Figure 7-19 Molex splitter

ATX

The original ATX power supplies had two distinguishing physical features:

the motherboard power connector and soft power. Motherboard power came

from a single cable with a 20-pin P1 motherboard power connector. ATX

power supplies also had at least two other cables, each populated with two or

more Molex or mini connectors for peripheral power.

When plugged in, ATX systems have 5 V running to the motherboard.

They’re always “on,” even when powered down. The power switch you press

to power up the PC isn’t a true power switch like the light switch on the wall

in your bedroom. The power switch on an ATX system simply tells the

computer whether it has been pressed. The BIOS or operating system takes

over from there and handles the chore of turning the PC on or off. This is

called soft power.

Using soft power instead of a physical switch has a number of important

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