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AMD's A8-3850 Fusion APU


Llano lands on the desktop
— 11:17 PM on June 29, 2011

Ever get the feeling you're in an ever-repeating scenario like the one from the movie Groundhog Day? That's been the mood here in Damage Labs lately. We finished our review of AMD's mobile A-series APUs, and then we turned around and began testing the desktop variants of the same chip. Apparently, we're being given the chance to write about APUs every day until we get it right. Trouble is, if our 10,000-word treatment of the mobile version wasn't sufficient, we're doomed to more sequels than a Ubisoft video game franchise. You see, the chip code-named "Llano" makes perfect sense in laptops, but its placement among desktop processors is somewhat more precarious.

The desktop A-series APUs
To understand why Llano's footing on the desktop isn't quite so sure as it is in laptops, you'll first want to understand the chip itself. Of course, we're going to point you to our massive and righteous coverage of the chip's architecture and implementation, first and foremost. For those of you who aren't, you know, really strong readers, we'll offer the Cliff's Notes version.

AMD calls this chip an APU, or accelerated processing unit, but most of the world would simply call it a highly integrated CPU, very much like its direct competition from Intel, the Sandy Bridge processors. Llano is AMD's first processor based on GlobalFoundries' 32-nanometer-plus-acronyms (SOI HKMG DSL) chip fabrication process, and the incredible transistor density offered by this process has allowed the integration of a whole host of functions into a single die. The chip's four CPU cores are a tweaked version of the "Stars" core found in Phenom II processors. A move to 1MB of L2 cache per core and some incremental improvements to the execution engine have netted a claimed 6% increase in per-clock instruction throughput. The "Sumo" integrated graphics processor is the spitting image of the discrete "Redwood" GPU used in the Radeon HD 5670, though its UVD video processing block has been updated with broader codec acceleration. An integrated memory controller gives both the CPU and GPU cores access to twin channels of DDR3 memory, and 24 lanes of second-gen PCI Express connectivity offer a path to expansion cards and peripherals. Oh, and there are dual display output paths, so the chip can drive two monitors at once.

Phew. That's a lotta stuff.

There are fairly straightforward reasons why a highly integrated chip like this one is best suited for laptops. Integration saves space and power, both of which are at a premium beneath a laptop's keyboard. Also, Llano's value proposition relies pretty heavily on its relatively beefy integrated graphics solution. In laptop, you're generally stuck with whatever GPU the system's manufacturer chose to use. On the desktop, where popping in a video card is literally a snap, questions must be asked about the worth of that IGP.

Anyhow, we'll explore those potentially difficult questions soon enough, but first we should discuss a number of other matters, starting with the basic specs of the new A-series APU lineup.


The A-Series models and key specs. Source: AMD.

The mobile versions of Llano are constrained by relatively tight 35W and 45W power and thermal envelopes, but the desktop versions get to breathe freely. As a result, both CPU and IGP clock speeds are substantially higher. The mobile A8-3500M we reviewed had a base CPU clock of 1.5GHz and a 444MHz IGP. By contrast, the desktop A8-3850's four cores run at 2.9GHz, and the IGP clock is up to 600MHz. Those gains come with a price, in the form of exponential increases in power consumption. The A8-3850 APU we have for review sports a very, um, healthy 100W TDP, nearly triple that of the A8-3500M.

We were expecting to see AMD's Turbo Core dynamic clock speed technology deployed across the Llano lineup, but it hasn't worked out that way. Only the 65W parts feature Turbo Core, while the 100W versions stick with the tried-and-true formula of aggressive base clock speeds.

AMD tells us the two 100W APU models shown above will start selling soon, although we'd better relay the exact wording, since it's a little slippery. The official statement says: "Global availability will begin to ramp July 3rd." It's possible availability may be wider in some international markets, particularly China, initially. When it does hit stores over here, the A8-3850 will set you back $135, while the A6-3650 will list for $115. (We don't yet have pricing on the 65W models, but AMD expects them to be priced pretty close to their 100W counterparts.)

The A8-3850 is the model we have on hand for review today, and its $135 list price puts it smack-dab between a couple of Sandy Bridge-based offerings from Intel. The most obvious competitor is the Core i3-2100, a dual-core, 3.1GHz processor that currently sells for $125. However, the i3-2100 is gimpy in one key area: graphics. The closer competition is a slightly newer model, the Core i3-2105, which has the exact same CPU specs but includes the fully realized HD 3000 version of the Intel IGP, with all 12 execution units enabled. Intel very quietly introduced the Core i3-2105 in May, probably because Llano was close on the horizon. The i3-2105 is going for $140 online, making it the most direct competitor to the A8-3850. We have both the i3-2100 and i3-2105 on hand for testing, of course.

Despite their similar pricing, the matchup between the A8-3850 and the Core i3-2100/2105 involves a little bit of asymmetrical warfare. Llano has four cores, while the Core i3 has two—though it does support four execution threads, thanks to Hyper-Threading. The Intel processors are based on a much smaller slab of silicon, and they'll fit into a much tighter 65W thermal envelope, as well.

For a lot of do-it-yourself PC builders, the A8-3850 may have an even more formidable challenger in the form of an incumbent offering from AMD. The Phenom II X4 840 has four cores at 3.2GHz, a 95W TDP, and sells for just $105 right now. That formula has made the X4 840 a favorite system guide rec here at TR. Of course, the X4 840 lacks integrated graphics, but for anyone looking to build a system with a discrete GPU, it may be the better choice.

As you might have guessed, Llano chips are probably more likely to make their way into relatively low-end systems, especially the type where a small footprint might be prized—small-form-factor desktops, all-in-one (AIO) systems a la the HP Omni series, and so on. For what it's worth, AMD expects A6-based systems to start at about $500 and A8-based ones to start at around $600. Also for what it's worth, we doubt many of those smaller PCs or AIOs will incorporate the 100W parts. The 65W parts are better suited to small-form-factor desktops and are likely to be more popular with the big PC builders. What's more, we think the 35W/45W mobile APUs are the better fit for all-in-ones.

We have one more sad duty to perform on the pricing and positioning front, and that relates to the Dual Graphics feature of the A-series APUs. As you may know, the Llano IGP can team up with a discrete GPU of similar power via AMD's CrossFire technology to deliver higher frame rates than either single GPU could achieve. In response to this fact, AMD's marketing folks have created a host of new brand names—some for the Llano IGPs, and others representing the combined power of the Llano IGP and a discrete GPU.

Confused? You'll be more confused once you understand it. Here, have a look at this table.

So here's the deal. The left column shows various models of discrete Radeon GPUs. Across the top are the two Radeon brands assigned to A8 and A6 APUs, Radeon HD 6550D and 6350D, respectively. In the middle, the strings with "D2" at the end show the model numbers of the combined Dual Graphics solution, which may be affixed to a PC at Best Buy.

This is the point where Scooby looks into the camera, tilts his head, and says "Ruh?"

But think about it. Now, all you need to do is look at the "Radeon HD 6550A2" sticker on a retail system, write it down, come home, and Google for it. Eventually, you'll find a chart like the one above. Then, you can correlate the 6550A2 to the combination of the integrated Radeon HD 6530D and the discrete Radeon HD 6450A. After that, you can attempt to find a desktop graphics card analogous to the Radeon HD 6450A in order to get a feel for its approximate performance. Several hours later, you can give up, secure in the knowledge that no one really knows.

We do, however, know that the A8-3850's IGP and our discrete Radeon HD 6670 interlock to become the Radeon HD 6690D2. Test results are forthcoming.