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Llano motherboards from Asus, Gigabyte, and MSI

Introducing the A75 Fusion controller hub

Fusion is way past due. Indeed, it took so long for the marriage of AMD and ATI to produce an offspring that combines a CPU and GPU on the same silicon die that Intel popped one out first. The Pineview Atom's CPU and GPU cores have shared the same silicon since 2009. AMD didn't release its first Fusion-based Zacate and Ontario processors until early this year, which is right about when Intel unleashed Sandy Bridge, the first CPU/GPU hybrid for real PCs rather than netbooks and ultraportables. More than six months later, Sandy finally has some competition from Llano, Fusion's second coming.

By now, you've no doubt read our coverage of the mobile variant of this Fusion APU, a so-called "accelerated processing unit" in AMD's hip new lingo for the next generation. You've probably also pored over the pages of test results that make up our in-depth look at how Llano fares on the desktop. Hold tight, because there's even more of this story to tell. Llano comes with a new Socket FM1 and A75 chipset, so it's hitting the desktop amidst a crowd of fresh motherboards eager to prove their mettle.

While AMD may not be able to claim a true first with Fusion (beyond, perhaps, being the first to combine a CPU with a good GPU), its A75 platform hub is thus far the only core-logic chipset to offer native USB 3.0 connectivity. That capability, combined with a stack of PCI Express 2.0 lanes and six 6Gbps SATA ports, makes the A75 a prime candidate for the budget and small-form-factor motherboards that seem perfectly suited to take advantage of Llano's strengths.

To get a better sense of the A75's performance characteristics, we've poked and prodded its integrated peripherals. We've also thrown a collection of affordable ATX and microATX motherboards—including Asus' F1A75-V PRO, Gigabyte's GA-A75M-UD2H, and MSI's A75MA-G55—into a cage match to see if one can emerge victorious.

Each board has a slightly different take on the budget formula. However, they're all based on the same A75 Fusion controller hub. Fabbed on an unassuming 65-nm process, this tiny piece of silicon consumes just 7.8W yet packs more cutting-edge peripherals than any other platform hub. Most of you will recognize it as a south-bridge chip.

With modern processors sporting their own graphics cores and north-bridge components, chipsets have been whittled down to single-chip I/O hubs. The A75 is about as modern as they come thanks to its integrated USB 3.0 controller. In addition to ten run-of-the-mill USB 2.0 ports, the chip has four of the SuperSpeed variety. The USB 3.0 ports are handled by separate controller logic that promises substantially higher transfer rates with portable hard drives and docking stations.

AMD gets a gold star for doling out four ports rather than skimping with two. All of the mobos in this round-up (and likely most of the A75-based mobos you'll find on the market) offer two USB 3.0 ports in the rear cluster and an onboard header that'll hook up to a case's front-panel connector for two more. Most auxiliary USB 3.0 controllers offer just two ports, making the A75's native solution all the more impressive. We'll see in a moment whether it can match the performance of some of those third-party alternatives.

The A75 is also stacked with third-generation Serial ATA connectivity. Otherwise known as SATA 6Gbps, this standard isn't new to AMD chipsets; support has been around since the SB850 south bridge, which was available more than a year ago. All half-dozen of the A75's SATA ports are 6Gbps, a trait of the controller design it shares with the SB850. Intel's 6-series chipsets, meanwhile, can push SATA speeds to 6Gbps on just two ports out of six.

If you were hoping to build a closet file server with Llano, note that the A75's RAID support is limited to 0, 1, and 10 arrays. RAID 5 is out despite the fact that it's supported by the SB850 and surely implemented in software rather than hardware. This parity-infused array type offers redundancy with a much more efficient use of disk capacity than either RAID 1 or 10, so it's a disappointing loss.

The A75 block diagram. Source: AMD

With competent graphics on the CPU and goodies like USB 3.0 and SATA 6Gbps permeating the chipset, few Llano-based systems will need auxiliary peripheral chips or expansion cards. Nevertheless, the A75 features four PCI Express 2.0 lanes reserved for slots and onboard devices. Four additional PCIe-like lanes are devoted to the link between Llano and the A75. Dubbed UMI, short for unified media interface, this interconnect offers 4GB/s of bidirectional bandwidth (2Gb/s in each direction) between the two chips.

As you can see in the block diagram above, Socket FM1 APUs have their own display interfaces, DDR3 memory controller, and PCIe lanes. Four of those lanes are available for general use, while 16 can be consolidated into a single link for discrete graphics cards. The 16-lane link can be split into a dual-x8 config for CrossFire, if the motherboard supports it, or a pair of Radeons will work together in an asymmetrical PCIe config when the second GPU is connected to the four other PCIe lanes stemming from the APU. Llano's integrated GPU can also be combined with select graphics cards in a special Dual Graphics CrossFire mode.

Obviously, there's a lot to say about all the features AMD integrates into the Llano APU. We're focusing on the chipset and motherboard in this article, but I highly recommend checking out our coverage of the notebook-bound A8-3500M for more on the APU's architecture. That review explores Llano's CPU and GPU components in much greater detail than we'll indulge here.

While the block diagram is still within scrolling distance, there are a few things I want to point out. The APU may be loaded with digital display circuitry, but VGA output gets piped through a digital-to-analog converter located in the chipset. The A75 also keeps around a legacy PCI controller for that Xonar DG sound card you've been craving. Most of Intel's recent chipsets have dropped the old expansion standard completely, forcing motherboard makers to employ secondary silicon just to offer PCI slots.

Finally, I'm going to get an early start on beating the fan-control drum by pointing out that the Llano platform—code-named Lynx, by the way—has some very promising fan-control logic. We've heard at least one motherboard maker call both the hardware and software side of AMD's implementation buggy, though. Perhaps that's why we haven't seen it implemented widely. Only one of the boards we're looking today uses the AMD logic to control the CPU fan.

A range of A75 options
Before taking a closer look at each board, I should pause to introduce them with a little context. The Asus F1A75-V PRO stands out the most, not just because it's the only one to use the full ATX form factor, but also because it costs $20-30 more than the others. That's a notable premium when the Llano line tops out with the $135 A8-3850 processor.

  Asus F1A75-V PRO Gigabyte GA-A75M-UD2H MSI A75M-G55
Form factor ATX microATX microATX
Expansion slots 2 PCIe x16 (x16, x4)
2 PCIe x1
2 PCIe x16 (x16, x4)
1 PCIe x1
2 PCIe x16 (x16, x4)
1 PCIe x1
Gigabit Ethernet Realtek RTL8111E Realtek RTL8111E Realtek RTL8111E
Auxiliary SATA ASMedia ASM1061 NA NA
Auxiliary USB 3.0 ASMedia ASM1042 NA NA
Audio Realtek ALC892 Realtek ALC889 Realtek ALC887
FireWire NA VIA VT6308 NA
Warranty length Three years Three years Three years
Price $130 $110 $100

To its credit, the PRO boasts additional USB 3.0 and 6Gbps SATA controllers. FireWire is only available on the Gigabyte GA-A75M-UD2H, which sits in the middle of our three-way throwdown. The UD2H offers a handful of upgrades over the MSI A75M-G55 for only $10 more.

As one might expect from the cheapest board of the lot, the G55's spec sheet is the most spartan. Keep in mind that the A75 chipset does a nice job of covering the essentials with little need for embellishment, though. MSI adds only a Gigabit Ethernet controller and an audio codec.