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NOTE Many manufacturers sell what they call BTX power supplies. These are actually marketing gimmicks. See Chapter 10, “Power Supplies,” for details.

Everything in the BTX form factor is designed to improve cooling. BTX cases vent cool air in from the front and warm air out the back. CPUs are moved to the front of the motherboard so they get cool air coming in from the front of the case. BTX defines a special heat sink and fan assembly called the thermal unit. The thermal unit’s fan blows the hot CPU air directly out the back of the case, as opposed to the ATX method of just blowing the air into the case.

The BTX standard is clearly a much cooler option than ATX, but the PC industry tends to take its time when making big changes such as moving to a new form factor. As a result, BTX has not yet made much of an impact in the industry, and BTX motherboards, cases, and thermal units are still fairly rare. BTX could take off to become the next big thing or disappear in a cloud of disinterest—only time will tell.

Proprietary Form Factors

Several major PC makers, including Dell and Sony, make motherboards that work only with their cases. These proprietary motherboards enable these companies to create systems that stand out from the generic ones and, not coincidently, push you to get service and upgrades from their authorized dealers. Some of the features you’ll see in proprietary systems are riser boards like you see with the NLX form factor—part of a motherboard separate from the main one, but connected by a cable of some sort—and unique power connections. Proprietary motherboards drive techs crazy because replacement parts tend to cost more and are not readily available.

Chipset

Every motherboard has a chipset. The chipset determines the type of processor the motherboard accepts, the type and capacity of RAM, and the sort of internal and external devices that the motherboard supports. As you learned in earlier chapters, the chips in a PC’s chipset serve as electronic interfaces through which the CPU, RAM, and input/output devices interact. Chipsets vary in features, performance, and stability, so they factor hugely in the purchase or recommendation of a particular motherboard. Good techs know their chipsets!

Because the chipset facilitates communication between the CPU and other devices in the system, its component chips are relatively centrally located on the motherboard (Figure 9-13). Most modern chipsets are composed of two primary chips: the Northbridge and the Southbridge.

Figure 9-13 Northbridge (under the fan) and Southbridge (lower right, labeled VIA)

The Northbridge chip on traditional Intel-based motherboards helps the CPU work with RAM, as mentioned in earlier chapters. On newer AMD and Intel-based motherboards, however, the Northbridge does not work directly with RAM, but instead provides the communication with the video card. The CPU has taken on the role of the memory controller. Current Northbridge chips do a lot and thus get pretty hot, so they get their own heat sink and fan assembly.

The Southbridge handles some expansion devices and mass storage drives, such as hard drives. Most Southbridge chips don’t need extra cooling, leaving the chip exposed or passively cooled with only a heat sink. This makes the Southbridge a great place to see the manufacturer of the chipset, such as Intel.

Many motherboards support very old technologies such as floppy drives, infrared connections, parallel ports, and modems. Although supporting these old devices was once part of the Southbridge’s job, hardly any modern chipsets still support these devices. Motherboard manufacturers add a third chip called the Super I/O chip to handle these chores. Figure 9-14 shows a typical Super I/O chip.

Figure 9-14 Super I/O chip on ASUS motherboard

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NOTE Super I/O chips work with chipsets but are not part of the chipset. Motherboard makers purchase them separate from chipsets.

The system ROM chip provides part of the BIOS for the chipset, but only at