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AMD's 785G integrated graphics chipset


A classic gets updated
— 11:00 PM on August 3, 2009

As a PC enthusiast, my attention naturally gravitates toward the bleeding edge. I can't help but want to see what's new, what's fast, and what's coming up next. These days, though, it's hard to justify lusting after a high-end system. The vast majority of applications are still single-threaded, and even those who multitask can generally get by with an affordable dual-core CPU. Additionally, the prevalence of games designed primarily for the dated hardware underpinning the current generation of consoles has ensured that you don't need to spend much more than a $150 to enjoy the latest games with all their eye candy enabled on monitors up to 24 inches.

Heck, if you don't play games, you don't even need to buy a graphics card. Today's integrated graphics chipsets are certainly up to the task of handling standard desktop applications, and they're endowed with high-definition video decoding capabilities. They even sport a couple of digital display outputs, should you wish to run a multi-monitor setup without futzing with analog conversions.

Even the motherboards based on modern integrated graphics chipsets are pretty good. Years ago, it seemed motherboards with integrated graphics were designed exclusively for system integrators and major PC brands looking to crank out budget systems with little flair and only the bare minimum of function. While adequate for mainstream folks, these boards were a little low-rent for enthusiasts. Fast-forward to the present day, however, and you'll find that the landscape has changed dramatically. You can now get full-featured integrated graphics boards loaded with BIOS tweaking and overclocking options, high-quality electrical components, plentiful I/O ports, and even dual PCI Express x16 slots.

Since enthusiasts have traditionally been gamers, few of us have stripped the discrete graphics cards from our primary desktops. We have, however, expanded the number of PCs in our homes, adding media-centric home theater PCs, closet file servers, and even little systems tucked away in our kitchens. These auxiliary machines tend not to play games, making them perfect candidates for integrated graphics.

Such as those provided by AMD's new 785G chipset, perhaps.

Descended from the 780G, our favorite integrated graphics chipset for the better part of a year and a half, the 785G's pedigree is impressive. That's important, because the 785G is very much like its predecessor.


Despite this strong family resemblance, the 785G is more than a marketing-driven model number uptick to denote support for the latest Socket AM3 processors. The chipset's north bridge component is all-new silicon, albeit built on the same 55nm node as its forebear, with roughly the same number of transistors. Some 205 million transistors made up the 780G's north bridge silicon, and AMD says that number hasn't gone up by much for the 785G.

So what does a modest increase in transistors get you? A new RV620 graphics core otherwise known as the Radeon HD 4200. As its name implies, this integrated GPU has all the enhancements one might expect from the Radeon HD 4000 series, including support for DirectX 10.1. However, the number of stream processors remains the same. Like the Radeon HD 3200 found inside the 780G, the 4200 GPU has 40 stream processors ticking at 500MHz. They don't run at that speed all of the time, though; the 785G's PowerPlay energy saving scheme constantly adjusts clock speeds based on GPU utilization, bringing the core down to just 60MHz when idling. Indeed, all the internal clocks inside the 785G scale dynamically to save power, although chipset voltages remain constant.

Rather than having the 785G's integrated Radeon cannibalize system memory bandwidth and capacity, motherboard makers have the option of pairing it with dedicated "sideport" memory of its own. Sideport memory was an option on the 780G, too, but few mobo makers took advantage of it. AMD says that has changed with the 785G, with more boards expected to sport dedicated video RAM.

Much like its 3D core, the Radeon HD 4200's Universal Video Decoder (UVD) has also been tweaked. This second-gen UVD block retains the original's ability to handle the lion's share of processing associated with Blu-ray playback across all three common formats. Now it can apply that decode acceleration to multiple streams, which is perfect for the picture-in-picture commentary tracks included with some new movies. Also new in the 785G's UVD is the ability to perform detail enhancements on the fly.

In another nod to the home theater PC crowd, AMD has upgraded the 780G's HDMI 1.2 support to version 1.3 for the 785G. However, the new chipset retains its predecessor's inability to pass uncompressed multi-channel LPCM audio over HDMI—a capability competing integrated graphics chipsets possess. The 785G can't pass TrueHD or DTS-HD audio over its HDMI output, either.


Although its embedded Radeon is really the star of the show here, the 785G is more than just a GPU. The chipset's north bridge component also houses a 2GHz HyperTransport link compatible with the latest Socket AM3 processors. It also has 22 second-generation PCI Express lanes split between a single x16 link for graphics and six x1 links for expansion slots and onboard peripherals. The chipset can't split its x16 link in order to feed a pair of x8 connections, though. That will force motherboard makers to get creative if they want to support CrossFire configs that extend beyond pairing an ultra-low-end Radeon with the integrated GPU. The Radeon HD 4200 can't participate in CrossFire configs with discrete graphics cards that posses substantially more horsepower.

Like the rest of AMD's core-logic lineup, the 785G uses PCI Express to link its north and south bridge components. A pipeline offering 2GB/s of bi-directional bandwidth sits between the 785G and its SB710 sidekick.


The SB710 is essentially an SB750 without support for RAID 5 arrays. The chip still has six 300MB/s Serial ATA ports, but they're limited to RAID 0, 1, and 0+1. AMD also throws in a single ATA channel so mobo makers don't have to use auxiliary peripheral chips just to provide an IDE port.

A dozen USB ports and a high-definition audio interface round out the SB710. Support for next-gen USB and SATA standards would have been nice here, but keep in mind we're talking about a budget chipset targeted at sub-$100 motherboards.