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Four Socket AM3 motherboards collide

Asus, Gigabyte, Jetway, and MSI in the hizz

The birth of AMD's Phenom processor was a difficult one. The first chips debuted at slower clock speeds than expected, and their performance was further crippled by a patch for the infamous TLB erratum. That didn't give AMD's new microarchitecture much of a chance against Intel's mature Core 2 line, which offered better performance, lower power consumption, and a more attractive overall value proposition. No wonder the original Phenoms never made the starting lineup for any of the builds in our regular system guides. Instead, they were relegated to the bench as alternates.

Fortunately for AMD, much has changed in the nearly 18 months since the Phenom's official launch. The processor's second coming has arrived, as has a new Socket AM3 designed for DDR3 memory. Aggressive pricing has allowed the Phenom II to deliver surprisingly solid value when compared to its Core 2 rivals. AMD has added new wrinkle in the form of the Phenom II X3 720 Black Edition, too. This triple-core chip runs at 2.8GHz, has an unlocked upper multiplier and loads of apparent overclocking headroom, and sells for an affordable $150.

The X3 720 is such a good value that it's cracked Intel's dominance of our mid-range system guide build. Indeed, our latest guide's ~$750 Utility Player system features the triple-core Black Edition as our primary recommendation.

In that particular system, we've taken advantage of the Phenom II's backward compatibility with older AM2+ sockets and paired it with a lower-cost DDR2 platform. Socket AM3 is the future for Phenom II, though, and thanks to falling memory prices fueled by Intel's Core i7 launch, DDR3 has quickly become a reasonable option, even for frugal enthusiasts.

Naturally, running a Phenom II with DDR3 memory requires a motherboard upgrade. Socket AM3 boards have started trickling onto the market, and we've thrown a trio from the usual suspects—Asus, Gigabyte, and MSI—into the ring with a wild card from Jetway to see whether we can find the best Socket AM3 platform for a Phenom II build.

Lining up the competition
The four boards we've gathered today are based on two different chipsets, both of which come from AMD. Nvidia does have an nForce 980a chipset designed for Socket AM3, but it was launched very quietly and looks to be little more than a repurposed nForce 780a. Shocking, I know. The 980a doesn't appear to be available on retail motherboards just yet, anyway.

In today's stable, we have two boards based on the 790GX chipset and another two based on the 790FX. The Asus M4A78T-E and Jetway HA08 opt for the 790GX, which has enough gen-two PCI Express lanes for dual-x8 CrossFire configurations, in addition to an integrated Radeon HD 3300 GPU. This integrated GPU uses the same graphics component as AMD's 780G chipset, but its core clock speed has been raised to 700MHz and it's been paired with 128MB of dedicated "Sideport" memory. Both of those factors conspire to improve the integrated Radeon's performance dramatically, although it still lacks the horsepower to play the latest games with detail levels turned up, even at modest resolutions. Fortunately, the Radeon HD 3300 also features a video decode engine capable of smooth Blu-ray playback, even with a low-end CPU. For more on the 790GX's integrated GPU and its performance, see our initial review of the chipset.

The 790GX's graphics component makes it either a flexible jack of all trades or a little confused, depending on your perspective. By contrast, the 790FX is a more focused product. This high-end core logic package does away with the GX's integrated GPU and adds enough PCI Express lanes to enable dual-x16 CrossFire setups. Gigabyte's GA-MA790FXT-UD5P takes advantage of these additional PCIe lanes by serving up a pair of full-bandwidth x16 slots. The Asus and Jetway boards have dual x16 slots, too, but they only get eight lanes of bandwidth each when both slots are in use. MSI's approach is quite different, with the 790FX-GD70 splitting its PCI Express lanes between four physical x16 slots, each of which offers eight lanes of connectivity in a four-way config.

Asus M4A78T-E Gigabyte GA-MA790FXT-UD5P Jetway HA08 MSI 790FX-GD70
Chipset AMD 790GX AMD 790FX AMD 790GX AMD 790FX
DIMM slots 4 240-pin DDR3 4 240-pin DDR3 4 240-pin DDR3 4 240-pin DDR3
Expansion slots 2 PCI Express x16
2 PCI Express x1
2 32-bit/33MHz PCI
2 PCI Express x16
3 PCI Express x1
2 32-bit/33MHz PCI
2 PCI Express x16
2 PCI Express x1
2 32-bit/33MHz PCI
4 PCI Express x16
1 PCI Express x1
2 32-bit/33MHz PCI
Auxiliary storage NA Gigabyte GSATA2 NA JMicron JMB322
Networking Atheros L1E 2 x Realtek RTL8111DL Realtek RTL8111CVC 2 x Realtek RTL8111DL
Audio VIA VT1708S Realtek ALC889A Realtek ALC888 Realtek ALC889
Firewire VIA VT6315N T.I. TSB43AB23 NA VIA VT6315N

Despite differences in PCIe payload and integrated graphics, the 790GX and FX both share the same SB750 south bridge component. The SB750 has a competitive feature set, with six Serial ATA RAID ports, a dozen USB ports, and an HD audio interface. However, the chip's storage controller is largely unchanged since the old SB600, and its AHCI support has never quite worked right. In our own testing, we've seen that getting ACHI performance to scale effectively via Native Command Queuing incurs a sizable CPU utilization penalty. Perhaps that's why AMD recommends running the SB750's storage controller in plain old IDE mode. Of course, IDE mode gives up support not only for command queuing, but for SATA hot plugging, as well.

The Gigabyte and MSI boards bolster the SB750 with auxiliary SATA controllers. Both ultimately use JMicron JMB322 chips, although the UD5P hides its pair behind a "GSATA" chip that's actually just a Silicon Image controller in disguise.

As the most expensive boards of the bunch, the Gigabyte and MSI models unsurprisingly feature dual Gigabit Ethernet controllers, with two of Realtek's RTL8111DL GigE chips on each board. Another Realtek networking component—this time the RTL8111CVC—graces the Jetway board. That leaves the Asus as the only one without something from the crab; the M4A78T-E sports a Gigabit controller from Atheros instead.

Realtek's dominance of the motherboard peripheral market continues on the audio front. Gigabyte and MSI employ versions of the ALC889 codec, although only the former takes advantage of its support for real-time Dolby Digital Live encoding. Jetway taps a lesser ALC888 codec chip, which unlike the 889s, can't play back lossless Blu-ray audio. This is the first we've seen of the VIA VT1708S used by Asus. This chip looks to be a pretty run-of-the-mill 8-channel HD audio codec, and we'll see how it does in our signal quality tests in a moment.

We'll look at Firewire performance, too, so don't worry if you don't recognize the VT6315N or the TSB43AB23. In fact, perhaps, worry if you do. And note that the Jetway board doesn't have a Firewire chip at all. That's to be expected given that it's the cheapest of the bunch by nearly $30. The Asus board rings up nicely in the middle of the pack at $140, while our 790FX-based Gigabyte and MSI boards square off at $180.