Datasheet

50 Chapter 1
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Hardware
A 20-pin main connector from the power supply to the motherboard is standard for all
ATX power supplies. In addition to this connector, many will include an auxiliary power
connector of either 4 or 6 pins to provide additional power.
In 2004, the ATX12V 2.0 standard was passed, changing the main connector from 20 pins
to 24. The additional pins provide +3.3V, +5V, and +12V (the fourth pin is a ground) for use
by PCIE cards. When a 24-pin connector is used, there is no need for the optional 4- or 6-pin
auxiliary power connectors.
Exam Essentials
Learn to troubleshoot power supplies. Be able to think through common power supply
problems and know that when you replace one you should check the voltage selector switch
and set it properly.
Recognize power-supply problems. Become familiar with the symptoms of a dead, failing,
or overloaded power supply.
Cooling Methods
The cooling system consists of the fan in the power supply, the fan or heat sink on the
CPU, and any additional heat sinks or fans in the case. If a system is inadequately cooled,
lockups and spontaneous reboots may occur.
Critical Information
Air cooling is the most common cooling method used in PCs. CPUs typically have active
heat sinks, which are heat sinks that include an electric fan that constantly channels heat
away. A CPU that is running too hot may benefit from a better cooling fan. The heat sink
portion is a block of spikes that channel heat away from the CPU.
Most passive heat sinks (that is, heat sinks that don’t include a fan) are attached to the
CPU using a glue-like thermal compound. This makes the connection between the heat
sink and the CPU more seamless and direct. Thermal compound can be used on active heat
sinks too, but generally it isn’t because of the possibility that the fan may stop working and
need to be replaced. Thermal compound improves thermal transfer by eliminating tiny air
pockets between the heat sink and CPU (or other device like a northbridge or video chipset).
Thermal glue provides both improved thermal transfer and adds bonding for heat sinks
when there are no mounting holes to clamp the heat sink to the device to be cooled. Clamps
or screws are commonly used to attach heat sinks to CPUs; therefore thermal compound is
used more often than thermal glue for CPU active or passive heatsinks.
In addition to the main fan in the power supply, you can install additional cooling fans
in a case to help circulate air through the case.
Liquid-cooled cases are available that use circulating water rather than fans to keep
components cool. These cases are typically more expensive than standard ones and may
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