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The platform


Block diagram of the "Sabine" platform. Source: AMD.

The Llano platform has its own code name, as well: "Sabine." Thanks to Llano's broad integration of components, the Sabine platform is a two-chip solution that should have a smaller footprint than AMD's prior efforts in this segment. AMD calls the single support chip in its APU platforms a "Fusion controller hub" or FCH, although the FCH is essentially the same thing as a traditional south bridge.

AMD offers two FCH options for Sabine. The A60M chip, already widely used in the low-cost "Brazos" platform, may see duty in relatively inexpensive Llano systems. We'd expect the A70M to be more prevalent thanks to its support for up to four USB 3.0 ports, a nice-to-have and much-needed feature distinguished by the fact that it's not natively provided by Intel's Sandy Bridge platforms. For external hard drives and other devices capable of high-speed transfers, USB 3.0's roughly 10X theoretical improvement over USB 2.0 can be a godsend.

AMD has built several features into the Sabine platform to make it more attractive. One is a dynamic screen brightness capability known as adaptive backlight modulation (ABM). ABM analyzes the image to be displayed and, when possible, reduces the backlight strength while raising the brightness of the pixels being displayed. The goal is to deliver a similar-looking on-screen image while using less power to drive the LCD, extending battery life.

Another feature of note is a dynamic switchable graphics facility. Although it has a relatively powerful IGP, as these things go, Llano can be paired with a discrete GPU for higher-performance graphics. As with prior platforms, the system can switch between the integrated and discrete GPUs in order to save power or to deliver better frame rates, either via user direction or by making an automatic swap to the IGP when on battery power. What's new here is another alternative, a dynamic switching capability that will choose the most optimal GPU based on application profiles. For instance, a session of web surfing in the GPU-accelerated IE9 might use the lower-power Sumo IGP, which is adequate to the task, but firing up a game would cause the system to hand off rendering duties to the discrete GPU.

In our experience, the dynamic switching feature works pretty seamlessly, transitioning between the responsible GPUs with little delay or drama. However, changing from one type of switching mechanism to another—from manual to dynamic or vice-versa—involved some garbled screens and big, hairy delays on our review system. Still, we expect most folks will choose dynamic switching and never look back, especially because the system prompts the user to pick the appropriate GPU for unrecognized applications.

Dynamic switching operates in conjunction with another intriguing feature, the innocuously named Dual Graphics, a mobile version of AMD's CrossFire multi-GPU teaming technology. AMD says the Llano IGP can cooperate with discrete Radeons in both the 5000- and 6000-series lineups. We've seen various attempts at teaming IGPs with discrete GPUs in the past, and they've been pretty uneven in terms of long-term support and compatibility. This incarnation comes with a big caveat right out of the starting gate, because it only works with games using DirectX 10 or 11. A great many games still use DX9, so Dual Graphics' applicability is narrower than we'd like. Still, if the difference in throughput between the IGP and the discrete GPU isn't too large, GPU teaming potentially makes some sense.

On evenly matched discrete GPUs, the preferred and most common method of divvying up the workload is to assign even-numbered frames to one GPU and odd-numbered ones to the other, a method known as alternate-frame rendering (AFR). On a pair of equally fast GPUs, AFR can achieve nearly twice the frame rate of a single chip. In the case of an IGP + GPU pairing that's somewhat asymmetrical, performance isn't likely to scale as well. AMD quotes a figure of "up to 75% additive performance" with Dual Graphics, and that's a best-case number. To overcome more extreme asymmetry between IGP and GPU, Dual Graphics can use a 2:1 split in frame assignments between the discrete and integrated GPUs. You're looking at more modest frame rate gains in such a configuration, but as Demers pointed out in a bit of a competitive dig, that's better than Nvidia's discrete GPUs, which can't gain any additional performance by splitting the workload with IGPs from Intel or AMD. Whether Dual Graphics is useful for things other than scoring marketing points is something we'll have to explore for ourselves.