The tech behind AMD's A-Series Fusion chips

14th Jun 2011 | 14:21

The tech behind AMD's A-Series Fusion chips

Why AMD's latest chips mean serious gaming on budget laptops

AMD has delivered its second Fusion processor – combining four CPU cores with powerful HD graphics on the same chip. The new Sabine platform, which the A-Series is part of, kills Intel's Sandy Bridge on graphics performance in midrange laptops. We've tested it, but what's the tech behind it?

The A-Series – previously codenamed as Llano - is what AMD refers to as an APU – an Accelerated Processing Unit. It's a combination of the CPU and GPU, just as Sandy Bridge is, but AMD's graphics experience (gained from its 2006 takeover of ATI) really begins to tell.

The A-Series is a cheaper chip than Intel's higher end Core i lines, designed for low-cost laptops. Quite how much laptops featuring the A-Series will cost remains to be seen - we'll know more on this in the coming days.

There are two variants of the A-Series 32nm die, one with 1.4 billion transistors and the second with 758 million. While the versions already announced are quad-core,

AMD will follow this up with a dual-core variant which it is currently tight-lipped about – some of these will no doubt be rejected quad-core units.

Much of the Core i3, Core i5 and Core i7 line will still outperform the A-Series for CPU performance as we saw in our review, but it's in graphics where AMD's new chip hits a home run. In the top A-Series chip, the 3500M, the graphics core is known as the Radeon HD 6620G and has all 400 cores enabled and runs at up to 444MHz. As Jeremy Laird says in our review, "it absolutely destroys Intel's equivalent integrated graphics core, the HD 3000".

"Trust me, this is really discrete-level graphics. This isn't only about gameplay, it's about features," said AMD general manager Rick Bergman at the recent Llano launch event attended by TechRadar.

Rick bergman

"By this time next year, 90 per cent of our processors will be APUs."

"The world of graphics changed 10 years ago. It's no longer about GHz," Bergman says. "You have to look deeper. We've dedicated almost half the die to our GPU technologies." The A-Series is fully DirectX 11 graphics compliant, rather than the DirectX 10-capable Sandy Bridge. AMD has already sold more than five million of the original Bobcat Fusion C and E Series CPUs since late 2010. These have been put into netbooks under HD graphics branding.

The A-Series chips offer some serious computing power, with up to 400 gigaflops of compute power in notebooks and up to 500 gigaflops in desktops. And, what's more, the tech will be expanded to lower power devices in due course. "Fanless APUs are on the horizon," predicts Bergman. "We can actually expand this to tablets… later in the year. Devices with an entirely different level of capabilities"

Another boon of the A-Series is battery life. AMD cites up to 10.5 hours are possible, though we got around 6.5 hours on our whitebook test machine running 720p video for that period.

"We're delivering Fusion supercomputing power in a notebook that lasts all day," continued Bergman. "There [has been] scepticism. AMD [has previously] struggled with battery life. Two years later, we're delivering on that promise."

Rick bergman

"We actually have two links into our GPU into the Northbridge. GPU performance scales with memory bandwidth, so we have this direct path through the Northbridge to the DDR, this gives the GPU priority access to access the system memory with high bandwidth – the Radeon Memory Bus."

AMD llano

The new platform also supports HDMI 1.4a, DisplayPort 1.1 and USB 3.0 to drive multiple displays and devices. AMD has also done a lot of power saving work including its Turbo Core Technology, which dynamically optimises or boosts CPU and GPU performance depending on the applications being run. AMD claims up to 10 per cent faster than Intel for USB 3.0 transfers.

AMD llano

Llano utilises AMD's Stars core design. Llano has up to four Stars cores, the Radeon graphics cores, 1MB of independent L2 cache per core, plus an integrated Northbridge, Unified Video Decoder ("this is the block that helps us do multimedia playback at very good power levels"), dual-channel DDR3 support, 24 PCI Express (Gen2) lanes and dedicated digital display interfaces (there's support for HDMI, DisplayPort and DVI). It all represents around "12-14 months of engineering effort" according to Bergman.

AMD llano

Fusion Compute Links enable the GPU to access coherent cache and memory. "It's the same I/O path that other devices use, but as it's internal we can plumb it better. Our APIs like Open CL can better share memory with the CPU."

AMD has also introduced a feature called Steady Video with the A-Series that's designed to stabilise videos during playback – making unsteady content look steadier.

John Taylor, Director of Product Marketing, told us that the lower end A4 parts will start at a sub-$300 price point. Taylor says that the sweet spot for the platform is in pitching the A6 chip against Intel's Core i3. "That's four cores versus two and we've got better battery life."

"Intel has flirted with [promoting on] 'ditch the discrete'. We will be marketing on full DirectX 11 support with the 320 Radeon cores from the A6."

"We light those pixels up better and more beautifully than anyone else in the industry."

AMD says the new APUs will appear in over 150 laptops and destops during the coming months and you'll see the A4, A6 and A8 processors appear under the AMD Vision branding. We're trying to get hold of a desktop setup at the moment and will review that as soon as we can.

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