CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [148]
Another notable connector is the auxiliary PCI Express (PCIe) power connector. Figure 10-24 shows the 6-pin PCIe power connector. Some motherboards add a Molex socket for PCIe, and some cards come with a Molex socket as well. Higher-end cards have a dedicated 6-pin or 8-pin PCIe power connector. The 8-pin PCIe connector should not be confused with the EPS12V connector, as they are not compatible. Some PCIe devices with the 8-pin connector will accept a 6-pin PCIe power connection instead, but this may put limits on their performance. Often you’ll find that 8-pin PCIe power cables have two pins at the end that you can detach for easy compatibility with 6-pin devices.
Figure 10-24 PCI Express 6-pin power connector
Practical Application
Niche-Market Power Supply Form Factors The demand for smaller and quieter PCs and, to a lesser extent, the emergence of the BTX form factor has led to the development of a number of niche-market power supply form factors. All use standard ATX connectors, but differ in size and shape from standard ATX power supplies.
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NOTE You’ll commonly find niche-market power supplies bundled with computer cases (and often motherboards as well). These form factors are rarely sold alone.
Here are some of the more common specialty power supply types:
TFX12V A small power supply form factor optimized for low-profile ATX systems
SFX12V A small power supply form factor optimized for systems using Flex-ATX motherboards (see Figure 10-25)
CFX12V An L-shaped power supply optimized for microBTX systems
LFX12V A small power supply form factor optimized for low-profile BTX systems
Figure 10-25 SFX power supply
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EXAM TIP The CompTIA A+ exams test you pretty heavily on power supplies. You need to know what power supply works with a particular system or with a particular computing goal in mind.
Active PFC Visualize the AC current coming from the power company as water in a pipe, smoothly moving back and forth, 60 times a second. A PC’s power supply, simply due to the process of changing this AC current into DC current, is like a person sucking on a straw on the end of this pipe. It takes gulps only when the current is fully pushing or pulling at the top and bottom of each cycle and creating an electrical phenomena—sort of a back pressures—that’s called harmonics in the power industry. These harmonics create the humming sound you hear from electrical components. Over time, harmonics damage electrical equipment, causing serious problems with the power supply and other electrical devices on the circuit. Once you put a few thousand PCs with power supplies in the same local area, harmonics can even damage the electrical power supplier’s equipment!
Good PC power supplies come with active power factor correction (active PFC), extra circuitry that smoothes out the way the power supply takes power from the power company and eliminates harmonics (Figure 10-26). Never buy a power supply that does not have active PFC—all power supplies with active PFC proudly show you on the box.
Wattage Requirements
Every device in a PC requires a certain amount of wattage to function. A typical hard drive draws 15 watts of power when accessed, for example, whereas some Athlon 64 X2 CPUs draw a whopping 110 watts at peak usage—with average usage around 70 watts. The total wattage of all devices combined is the minimum you need the power supply to provide.
Figure 10-26 Power supply advertising active PFC
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EXAM TIP The CompTIA A+ Certification exams do not require you to figure precise wattage needs for a particular system. When building a PC for a client, however, you do need to know this stuff!
If the power supply cannot produce the wattage a system needs, that PC won’t work properly. Because most