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PC Hardware in a Nutshell, Second Edition by Barbara Fritchman Thompson, Robert Bruce Thompson

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Power Connectors

All power supplies provide two types of power connectors. The first powers the motherboard and differs according to form factor. The second powers drives and other internal peripherals, and comes in two varieties, which are described below. Tower/AT and Tower/BAT power supplies include a third type of power connector—a high-voltage cable that connects the power supply to an external main power switch.

AT Main Power Connector

Table 26-6 lists the standard AT Main Power Connector pinouts used by all AT power supply variants, including Desktop/AT, Tower/AT, Desktop/BAT, Tower/BAT, and LPX. PC/XT power supplies use the same pinouts, except that pin P8-2 is unused. In addition to supplying various standard voltages, this connector includes a special-purpose pin. Pin P8-1, PG, carries the Power Good signal, which the power supply asserts once it has started and stabilized. The motherboard will not attempt to boot until the power supply asserts PG.

Table 26-6. Standard motherboard connector pinouts for an AT power supply

Pin

Color

Signal

Pin

Color

Signal

P8-1

orange (white)

PG

P9-1

black

ground

P8-2

red

+5V

P9-2

black

ground

P8-3

yellow

+12V

P9-3

white (blue)

-5V

P8-4

blue (brown)

-12V

P9-4

red

+5V

P8-5

black

ground

P9-5

red

+5V

P8-6

black

ground

P9-6

red

+5V

Note that P8 and P9 are separate connectors from the power supply, but mate to a combined connector on the motherboard.

Warning

The P8 and P9 connectors are individually ...

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