BUILD YOUR SYSTEM
The big decision here is choosing a motherboard with the right chipset. Typically consisting of two chips (the Northbridge and Southbridge), the chipset determines various factors such as memory speeds, expansion-slot capabilities, and bus speeds. Intel, AMD, and nVidia are among the chipset manufacturers you'll encounter. The easiest way to determine the features of a chipset is to look at the motherboard's feature list. Chipset characteristics will be reflected by the board's capabilities: how many graphics-card slots are offered, whether Serial ATA (SATA) drives are supported, how many networking ports are available, and so on. If you want to use the newest technologies, such as processors with a fast front-side bus (FSB) or multiple graphics cards, you'll need to pick a board with a chipset that that supports them. We suggest sticking with the latest chipset revisions, such as Intel's G, P, and X series; nVidia's 630i and 750/780i; and AMD's 7-series. Choosing motherboards based on these newer chipsets will give you the latest features and possibly spare you from having to replace your motherboard in 18 months when you're ready to upgrade again.
MEMORY MATTERS
If you're using memory from your previous computer on your new motherboard, choose a board with DDR2 memory support (unless your old PC is really ancient and uses plain old DDR—at which point, it's time to buy new RAM). High-end Intel-chipset boards are available in both DDR2 and DDR3 memory-slot varieties. DDR2 memory remains dramatically less expensive than DDR3 for the moment, but DDR3 offers faster speeds and the most potential for future upgrades. A few manufacturers, such as Gigabyte, offer boards such as the GA-X38-DQ6, which has sockets for both DDR2 and DDR3, allowing you to use older memory now and upgrade after prices drop.
Currently, Intel-based boards are the only ones that can make use of DDR3 memory, though AMD plans to introduce support for the new memory in 2009.
THE SLOT MACHINE
Gamers looking for top graphics per-formance will want to ensure that their motherboard offers at least one PCI Express (PCIe) x16 graphics-card slot. You can increase graphics performance further by installing multiple graphics cards. Unfortunately, while you can drop a single graphics card from any manufacturer into your graphics-card slot, current motherboards that can host multiple graphics cards support either nVidia's Scalable Link Interface (SLI) or AMD's CrossFire technology, but not both. Thus, if you want support for more than one card, you'll need to decide whether you're going to opt for SLI- or CrossFire-compatible cards and choose a board accordingly.
The newest motherboards let you go even further by adding up to three (3-Way SLI) or four (CrossFireX) video cards. You'll get the best performance if all of your video slots support x16 communications. Some dual-slot boards, such as those based on the Intel P35 chipset, run the second card in x4 mode, significantly slowing down multicard operation.
You'll also want to check that there are enough remaining slots to support any other cards you want to add. Many boards have plenty of PCIe slots, which often go unused, but skimp on slots that support the fading PCI standard. If you're building a home-theater PC and want to add, say, a pair of PCI TV-tuner cards and a PCI sound card, you'll need to ensure that your system has three open PCI slots, and that none of them is blocked if you're using a double-width video card.
SIZE MATTERS
Obviously, you need to make sure the board you choose will fit in your PC's case. Full-size motherboards use the ATX form factor, which defines standard dimensions for the board, as well as placement of mounting holes, components, and expansion slots. You can generally swap out any ATX board for another, though some variations in component placement can make for difficulties in small or nonstandard ATX computer cases. Also, some PCs from major manufacturers such as Hewlett-Packard and Dell use custom case-and-cooling combinations that might prevent installation of third-party motherboards.
MicroATX boards use the general ATX design, but they include fewer expansion slots, allowing for a shorter board that can fit in a smaller case. These are popular with builders of home-theater PCs, who are creating small computers for placement in their stereo racks.
Recent years saw a push to create a new standard, BTX, which moved board components around and dropped the power supply to the bottom of the case, with the aim of improving thermal management inside the PC. With the advent of cooler processors and buyers' resistance to a new standard, however, we're not seeing new BTX boards on the market.
POWER PLAY
One component that's a key companion to your motherboard—and one you're likely to need to replace if you're upgrading to a cutting-edge motherboard—is the power supply. Not only might your new setup require more wattage than the one it's replacing, but it might also use different power connectors. A few years ago, power supplies attached to motherboards using a single 20-pin ATX connector; now, that connection has grown to 24 pins. Then a second connector was added, commonly referred to as an "EPS/ATX12V" connector. It first appeared in a four-pin version, then with eight pins. All of the motherboards here require 24-pin ATX connectors, and while some can get by with the four-pin version of the EPS/ATX12V cable, a few require the full eight pins.
Your best bet is to purchase a power supply that's flexible. We used Corsair's new TX750W supply when testing boards for this article. It offers plenty of power, and, like with many new power supplies, both the ATX and EPS/ATX12V connectors are split into 20+4 and 4+4 pin configurations, accommodating motherboards old and new. It also includes four PCIe graphics-card connectors in a 6+2 configuration, allowing it to accommodate the newest video cards in CrossFire or SLI modes.
Don't skimp when buying a power supply. Though you can find generic power supplies with prices as low as their wattage ratings are high, these often don't provide clean, stable power. An inexpensive power supply may promise lots of watts, but once you start loading it up with hard drives, video cards, and a high-end processor, it may not pump out the necessary voltage. This can result in unpredictable system crashes and other reliability problems