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AMD's 780G chipset


Integrated graphics all grown up
— 8:01 AM on March 4, 2008

I've had a computer hooked up to my television for as long as I've had a living room. What would eventually be called a home theater PC had humble beginnings, starting its life tasked with simply playing movies and MP3s before eventually morphing into a personal video recorder and an occasional game box. Before long, living room gaming duties were offloaded to consoles, allowing years to pass with nary an upgrade to my media PC. So long has it been since I last cracked the case that a thin blanket of dust has draped itself across the system's internals, making the now-vintage hardware look all the more old and decrepit.

The HTPC market has exploded since I last built one. What was once an expensive accessory confined to enterprising geeks and do-it-yourself enthusiasts has moved into mainstream living rooms. And thanks to the relatively modest requirements of multimedia playback and recording, even today's budget hardware is up to the task—hardware like AMD's new 780G integrated graphics chipset.

The latest fruit borne of AMD's purchase of ATI packs a DirectX 10-compliant graphics core pulled from a Radeon HD 2400 graphics card, decode acceleration for HD DVD Blu-ray movie playback, second-generation PCI Express, Hybrid CrossFire, a new SB700 south bridge, and a Phenom-ready HyperTransport 3 processor link. All that's coming to motherboards that should cost less than $100. Alongside it, AMD is introducing a new energy-efficient Athlon X2 4850e with a 45W TDP and $89 price tag.

On paper, it looks like we have the recipe for a killer home theater PC or mainstream desktop. But has AMD nailed the execution this time around? We've run the 780G and 4850e through a grueling array of tests in order to find out.


New hotness all around
The 780G is a new chipset from its integrated graphics processor through the north bridge and all the way down to the south bridge. Of those components, the IGP is perhaps the most exciting. Dubbed the Radeon HD 3200, the integrated graphics core is ripped directly from the RV610 graphics processor that powers the Radeon HD 2400 series—a chip that was released just eight months ago. That's incredibly quick trickle down from budget GPU to integrated graphics chipset, making this the first IGP we've had that's really in step with the current generation of discrete GPUs.

Because it's a member of the same graphics family as AMD's discrete GPUs, the Radeon HD 3200 is also eligible for Hybrid Graphics configurations. The chipset's GPU can be teamed with a single graphics card—in this case either a Radeon HD 3450 or 3470—to improve performance in 3D applications. Hybrid CrossFire only delivers performance gains when GPUs of relatively similar horsepower are combined, which is why the Radeon HD 3200 IGP will only work in conjunction with the HD 3400 series of discrete GPUs.

Within the integrated Radeon HD 3200 graphics processor lies a unified shader architecture that spreads 40 stream processors across two shader SIMDs. Also included are single texture and ROP units capable of handling four texels and pixels per clock, respectively. The vertex and texture caches are shared to save die area (they're separate with most other R600-based designs), but the Radeon HD 3200 is still very much a DirectX 10-class part. If you think of the new Radeon HD 3800 series as a V8, the 3200 is essentially a single piston—one that runs at an impressive 500MHz and has access to up to 512MB of system memory.

Thanks to the 780G north bridge chip's HyperTransport 3 link, which scales up to 1.8GHz with AMD's current Phenom processors, the Radeon HD 3200 enjoys a very fat pipe to two channels of DDR2 memory at up to an effective 1066MHz. Motherboard makers can also equip the 3200 with dedicated memory of its own, an addition that AMD says can improve performance by 10-15%. Such support for local memory in an IGP isn't actually new, but it's a capability rarely exploited by motherboards that show up in retail. AMD claims tier-one mobo makers are, er, onboard to take advantage of it this time around, though.


The 780G block diagram. Source: AMD

HyperTransport bandwidth is apparently so important to the Radeon HD 3200 that AMD recommends a 1.8GHz link—currently available only with Phenom—to make the most of the graphics core. The 3200's post-processing engine for high-definition video playback actually requires the 1.8GHz HT link that Phenom provides. You don't need a Phenom to take advantage of the Radeon HD 3200's other video decoding capabilities, though. The integrated GPU's enhanced Universal Video Decoder (UVD) block is capable of handling decoding duties for high definition Blu-ray movies, and if you're a fan of the new Betamax, it'll do HD DVD too.

High-definition-ness is carried all the way through to the HD 3200's outputs, which include not only VGA and DVI, but also HDMI and even DisplayPort. HDCP is supported, as well, and the 780G is smart enough to be able to route S/PDIF audio through its HDMI output.

We've spent a lot of time on integrated graphics, but it's not the only element of the 780G's new hotness. The north bridge also gets 26 lanes of second-generation PCI Express connectivity, should you want to add a discrete graphics card of your own. 16 of those lanes are reserved for an x16 link, while six are distributed across x1 links meant for expansion slots and onboard peripherals. The remaining four links are reserved for the chipset's north bridge-to-south bridge interconnect.

Follow the interconnect south, and you're greeted by AMD's eagerly-anticipated SB700 south bridge chip, which ultimately arrives with a bit of a whimper. The SB700 may be new silicon, but in many ways, it's just more of the same. Take the chipset interconnect, for example. The 780G has four lanes of PCIe 2.0 reserved for its chipset link, and while the SB700 can match its northern neighbor's lane count, those PCI Express lanes come from the previous 1.1 generation. This caps north-south bridge interconnect bandwidth at 2GB/s—half of what it could have been with a top-to-bottom PCIe 2.0 implementation.

We quite literally see more of the same in the SB700's Serial ATA controller. The port count here is up to six, but they're basically six of the same ports you get on the old SB600. Drives can be configured in RAID 0, 1, and 10 arrays, but RAID 5 remains unavailable. This omission is notable because if you're a little paranoid about data loss, a three-drive RAID 5 might be a decent solution for a home theater PC.

On the USB front, the SB700 is up to 12 ports, this time with a dual-channel controller AMD says is faster than what can be found in the SB600. A couple of USB 1.1 ports are also included, apparently at the request of notebook makers who use them for various widgets.

The prospect of 780G notebook applications leads us nicely to the chipset's party piece: its power consumption. A very advanced—at least in chipset terms—55nm fabrication process is used to manufacture the chipset's north and south bridge components, bringing idle power consumption for the chips down to what AMD claims is less than one watt each.