The Big Picture
In many ways, the motherboard is the heart of the modern computer system, as it affects almost every other component. Choosing a motherboard is a fairly complicated task since you have seven to nine different factors to consider, of varying importance.
Take some time to think about how you'll use your system. Someone with a power meter that requires a serial port will care a lot more about the peripheral features than the average user will, while the hard-core gamer will probably focus on the GPU, CPU, and chip set while ignoring peripherals and form-factor issues.
CPU: The CPU, commonly referred to as the brains of a PC, is one of the key components (if not the key component) of a modern system. You have several mainstream options for your CPU. Intel currently has the highest-performing processor lineup, with the Core 2 Duo and the Core 2 Quad (which use the LGA775 socket). As the names imply, the Core 2 Duo is a dual-core CPU, while the Core 2 Quad is a four-core processor. AMD uses the AM2 and AM2+ socket and offers the Phenom (quad- or triple-core) and Athlon 64 (dual-core) CPUs. AMD's products are solid, but they generally provide lower performance. A lesser-known third player, Via Technologies, produces the low-power C7 processor; the C7 is a much less common option since it offers dramatically less performance than mainstream processors from Intel or AMD do.
Chip set: If the CPU is the brains of the PC, then the chip set is the spinal cord, responsible for tying together all of the different devices in the computer, and moving data among them. The chip set determines which CPUs, memory, and other devices can be used, and it can strongly influence performance.
The chip set is the single most important component of a motherboard. Since motherboards using the same chip set will usually have identical performance (barring serious design mistakes), they're differentiated by other features, such as the expansion slots, storage options, and other discrete chips that may be included.
Chip sets typically employ two different chips referred to as the northbridge and southbridge. Generally speaking, the northbridge is responsible for dealing with high-performance devices, while less-sensitive devices tend to cluster around the southbridge.
The northbridge traditionally includes the memory controller, plus integrated graphics or an interface for discrete graphics. (Note that AMD has the memory controller integrated into the CPU, rather than the chip set.) The southbridge includes networking, storage, audio, general peripherals, and other devices. The image here shows an example, the Intel X48 chip set with partitioning between the northbridge (or MCH) and southbridge (or ICH).
Memory: Selecting memory for your PC is usually a simple decision: You just pick a reliable brand that's as cheap as possible (unless you like overclocking, but that's a whole different story). Every so often, however, memory types undergo a transition--and one happens to be going on right now. Most chip sets use DDR2 memory at up to 800 MHz (PC2 6400), but newer chip sets from Intel may also use DDR3. DDR3 offers more bandwidth (1066 to 1600 MHz), consumes less power, and will be mainstream in a year, but for the moment it is more expensive. DDR3 is more likely to be useful for later upgrades, but it will carry a price premium until sometime in 2009.
Telling a DDR3 board from a DDR2 board without the manual or box isn't particularly easy, since both slots use 240 pins. The difference is that the key (a small gap between the pins) is closer to the center of the DIMM (the memory module) for DDR2, while it is closer to the edge of the DDR3 DIMM. Remember: If the memory module doesn't fit into the slot, don't force it!
Graphics hardware: The graphics hardware (the graphics processing unit, or the GPU) is the third-most-important component of a system, right after the CPU and chip set. The main considerations for graphics are cost, performance, and upgradability.
The lowest-cost option is a chip set with integrated graphics. Integrated graphics processors (IGP in industry parlance) are intended for basic 2D and 3D functionality and often use system memory instead of dedicated graphics memory. All of the major vendors (AMD, Intel, nVidia, and VIA) offer integrated graphics with some chip sets. An IGP is a fine choice for users interested in a little multimedia, office work, and other lighter workloads.
Integrated graphics will work fine for about 60 percent of the world, but the technology almost always lacks the performance necessary for gaming. For users who want to play on their PC, the next step up is a motherboard with a single PCI Express x16 slot, which accommodates a discrete graphics card from ATI/AMD or nVidia.
PCI Express comes in two flavors, Gen 1 and Gen 2. The difference is that Gen 2 PCI Express slots run at 5 GHz, twice the speed of the previous generation. That distinction doesn't particularly matter for current GPUs (or most other peripherals), but it will be an issue for upgrading in the future. For a motherboard that you expect to outlast the GPU you pair it with, springing for a faster PCI-E slot makes the most sense.
If price is no object and maximum gaming performance is your goal, your selection is a bit different. True multi-GPU support is a very high-end feature and is priced accordingly. The only options for multiple GPUs are SLI (for nVidia cards) or CrossFire (for ATI cards). Given that nVidia is the clear performance leader, SLI is the superior choice for now; note, though, that SLI works only with nVidia chip sets and Intel's Skulltrail motherboard.
A separate but related concern is the graphics interface. You have three major alternatives: VGA, DVI, and HDMI. VGA is the traditional 15-pin analog monitor connector, designed for CRT displays. DVI is a digital connector specifically intended for use with LCD monitors, and HDMI is a variant of DVI with the DRM (digital rights management) technology required to play Blu-ray and other high-definition media.
Sound: Integrated sound, which comes in two major flavors, will meet the needs of all but the most selective users and audio enthusiasts. AC97 is an older audio standard that has been superseded by HD Audio (or "Azalia"). You really have no reason to settle for the older standard, although the newer tech might carry a modest premium. For the dedicated enthusiasts who would benefit from a discrete sound card, an extra PCI-E slot is easy enough to find.
Storage: Like memory, basic storagetends to be relatively straightforward, but it gets tricky with some of the various options and platform transitions. In the past few years, storage experienced a transition from Parallel ATA to Serial ATA (SATA) and then to 3-gbps SATA. 1.5-gbps versus 3-gbps SATA can make a bit of a difference in performance, but typically only in video editing and other media-heavy workloads.
Most hard drives use SATA, while some older DVD+/-RW drives use Parallel ATA. Most motherboards support four or more SATA ports (even as many as ten), which is sufficient for most users.
eSATA is a relatively new standard for connecting external drives via SATA instead of FireWire or USB. eSATA offers higher performance than the other two, and also supports reliability and manageability features such as SMART (Self Monitoring And Reporting Technology). eSATA is not nearly as common as USB 2.0, but going forward it is likely to be more widely adopted, and it is certainly a better interface.
The other real storage issue concerns RAID, which is standard with many modern motherboards. You can use RAID 0 or 1 with two hard drives; the former increases read and write performance, while the latter increases reliability and read performance. RAID 5 requires at least three drives, and RAID 6 (which is really for businesses only) needs at least four; both are oriented around increased reliability and read performance, with acceptable write performance and less overhead than RAID 1. Most systems simply don't need that many drives, so in many ways 6 is a nice option but hardly a requirement. For video editing and other multimedia-rich tasks, basic RAID 0, 1, or 5 will do the trick and should be a requirement.
Networking: Wired networking is dead simple, as any worthwhile chip set will have at least one integrated gigabit ethernet port. For the most part, Wi-Fi is not necessary for desktops, and most motherboards tend to avoid it simply to cut down costs; it's an optional feature.
Assorted peripherals: On a motherboard, the peripherals can include USB 2.0, FireWire, PS/2, serial and parallel ports, and a floppy drive. Of those options, USB 2.0 is an absolute necessity and FireWire can be nice, but the rest are pretty much obsolete unless you need a a specific peripheral device.
Form factor: The last aspect of the motherboard to consider is the form factor. This is ultimately an aesthetic choice that the chassis for the system determines. Most motherboards use the ATX form factor, with the microATX design meeting the needs of space-conscious users. Quite a few other variants (which are beyond the scope of this article) are available for users with particular requirements, however.