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Bulldozer mobos from Asus and MSI: Sabertooth 990FX & 990FXA-GD80

Socket AM3+ arrives alongside AMD's 990FX chipset

Bulldozer is coming. AMD lifted the lid on its next-generation processor architecture in August of last year, and PC enthusiasts have been eagerly awaiting its arrival ever since. As one might expect from something named after a multi-ton piece of machinery pulled from the Tonka catalog, Bulldozer's approach has been a slow one. Some nine months after AMD's big reveal of the underlying architecture, the first Bulldozer-based Zambezi CPUs have yet to roll onto store shelves.

AMD's new baby may require a little more gestation before being released into the wild, but Taiwanese motherboard makers seem uninterested in waiting for its official arrival. I can't say I blame them. The Computex trade show takes over Taipei this week, giving mobo manufacturers the opportunity to show off their wares on home turf. Even if it tried, AMD probably couldn't have stopped Bulldozer boards from lining the show floor.

Besides, this incoming wave of Socket AM3+ motherboards is perfectly capable of getting by without Zambezi-based CPUs. The AM3+ socket is backward compatible with standard Socket AM3 processors, so any old Athlon II or Phenom II will do. Impatient fanboys looking to get a head start on their Bulldozer builds will have no shortage of options, and we've rounded up a couple of interesting ones from Asus and MSI.

In Asus' corner, the TUF series, of which we've grown fond, finally adds an AMD-compatible model in the Sabertooth 990FX. Meanwhile, MSI looks to continue its recent upward trajectory with the 990FXA-GD80. Both boards are lavished with all of the luxuries one might expect from high-end enthusiast models, such as military-class electrical components, UEFI replacements for legacy BIOSes, plentiful 6Gbps Serial ATA ports, loads of USB 3.0 connectivity, and enough PCI Express x16 slots for three-way CrossFire or SLI graphics configs. There are important differences between how Asus and MSI have approached this next-generation platform, though. We'll explore those differences over the following pages as we see how the Sabertooth 990FX and 990FXA-GD80 stack up against the latest and greatest Sandy Bridge motherboards.

New socket, same silicon
As far as Zambezi is concerned, the most important element of these new motherboards is the AM3+ socket. Ignore the AM3b label in the picture above. Despite what component maker Lotes would have you believe, the official name for AMD's new socket is AM3+.

At first glance, Socket AM3+ appears to be little more than an AM3 socket done up like Robert Downey Jr. in Tropic Thunder. Black is in, but it's not the only change. If you take the time to count, you'll notice that the AM3+ socket has 942 individual pins—one more than AM3.

Intel made the transition to an LGA socket all the way back in the Pentium 4 days, but AMD continues to put the pins on the processor rather than the motherboard. As someone who handles both components on a daily basis, I have to admit that I prefer the LGA approach. Processors tend to be more expensive than motherboards, so the cost of a bent pin is likely to be higher with a conventional socket. The fact that CPUs are much smaller and easier to mishandle also makes them more prone to accidental pin damage. To be fair, though, realigning a processor's bent pins can be easier than performing similar surgery on an LGA socket.

Sticking with a traditional socket allows AMD to maintain its long-standing tradition of offering some degree of backward compatibility when introducing new CPUs and sockets. As a result, Socket AM3+ motherboards will happily accept existing AM3 CPUs. The picture isn't quite as clear for folks hoping to pair upcoming AM3+ CPUs with older motherboards. Asus and MSI have announced BIOS updates for select Socket AM3 boards that promise compatibility with these next-gen processors. However, neither company has been able to confirm that those updates will allow boards to fully exploit the clock-scaling and power-saving features built into Zambezi. Asus expects everything to work properly, but it won't know for sure until the final CPU silicon is ready. With AMD intent on keeping the details of Zambezi's socket-specific mojo to itself until the CPU's official unveiling, there isn't much more we can add on the subject.

We can tell you that some motherboard makers have introduced Socket AM3+ models based on older 8-series chipsets, and that the presence of 942-pin sockets should guarantee Zambezi will properly. However, with only a + separating these boards from older AM3 models, there's plenty of potential for confusion. To provide some clarity, AMD is rolling out 9-series chipsets that will be available exclusively on Socket AM3+ motherboards.

Led by the 990FX, this core-logic family is new in name only. The 990FX consists of the same north- and south-bridge components as its 890FX predecessor, and those chips continue to be manufactured by TSMC using a 65-nm fabrication process. AMD didn't have a block diagram for the 990FX when we asked, but it only took a couple of minutes in Photoshop to put one together using the block diagram from our 890FX review.

My changes are not-so-subtly highlighted in pink, and there really isn't much to see. The old 890FX block diagram shows a HyperTransport 3.0 processor link with 5.2 GT/s of peak interconnect bandwidth. With the 990FX, that link gets upgraded to version 3.1 and 6.4 GT/s of bandwidth. Because the north-bridge silicon is unchanged, the fatter pipe is likely tied to the socket rather than the chipset. I'd expect AM3+ boards with 8-series chipsets to offer the same boost in HT link speed.

Despite building blocks that are more than a year old, the 8990FX looks very well equipped. The north bridge is essentially a massive PCI Express 2.0 switch loaded with 42 lanes of connectivity. 32 of those lanes can be split evenly between a pair of x16 slots, and the resulting x16 links can be cleaved in two to enable all kinds of multi-GPU excess. Speaking of multi-GPU configs, I probably should have added a couple of SLI logos to the block diagram. After years of preventing multiple GeForce graphics cards from sharing rendering duties on AMD chipsets, Nvidia has a new graphics driver that enables SLI support on 990FX motherboards.

At the south bridge, the SB950 offers a couple of additional PCI Express lanes alongside the usual assortment of I/O blocks. All six of the Serial ATA ports boast 6Gbps connectivity, but the USB controller is so last-generation. To be fair, Intel also stuck with USB 2.0 for its Sandy Bridge chipsets, which have just two 6Gbps SATA ports. Both firms have been slow to embrace the new USB standard, even though it's an arguably more necessary step up in performance than the transition from 3Gbps to 6Gbps SATA. Just about any external hard drive should be fast enough to saturate a USB 2.0 connection, but you'll need a high-end SSD to saturate the bandwidth offered by a 3Gbps SATA port.

And then there were two
As we do before most major chipset launches, we pinged The Big Three motherboard makers to see what they had to offer. Only Asus and MSI were able to provide boards before my flight for Computex left on Saturday morning, so sadly, Gigabyte will have to sit this one out.

  Asus Sabertooth 990FX MSI 990FX-GD80
CPU power 8+2 8+2
Expansion slots 3 PCIe x16 (x16/x16, x16/x8/x8)
1 PCIe x16 (x4)
1 PCIe x1
3 PCIe x16 (x16/x16, x16/x8/x8)
1 PCIe x16 (x4)
2 PCIe x1
Gigabit Ethernet Realtek RTL8111E Realtek RTL8111E
Auxiliary SATA 2 x JMicron JMB362 JMicron JMB362
USB 3.0 2 x ASMedia ASM1042 2 x NEC D720200
Audio Realtek ALC892 Realtek ALC892
FireWire VIA VT6308P VIA VT6315N
Warranty length Five years Three years
Price $209 $200

At least on the surface, the Sabertooth 990FX and 990FXA-GD80 are quite similar. The boards sport the same number of power phases and PCI Express x16 slots, and they rely on identical controllers to handle audio, Gigabit Ethernet, and auxiliary Serial ATA duties. There's some variety on the USB 3.0 front, with MSI opting for NEC's near-ubiquitous controller, while Asus uses a new chip from subsidiary ASMedia.

One of the most notable differences between these two motherboards is the Sabertooth's five-year warranty, which has yet to be matched by desktop boards outside Asus' TUF series. The additional coverage is a nice bonus for folks who upgrade infrequently or migrate older hardware to secondary systems like HTPCs, closet file servers, and PCs for the rest of the family. You'll pay a little extra for the privilege, though.