785G Chipset Features
So is ATI's latest chipset a Radeon 3000 series product, as the 785G designation implies or is it a Radeon 4000 series part? It's a bit of both, but we'd definitely call it an extension of the 780G architecture instead of a new RV7xx integrated part.
Fundamentally the architecture of the graphics core itself is pretty similar to the GPU found in the 780G's Radeon 3200 graphics. You've got the same 40 stream processors with 4 texture units and 4 ROPs as the 780G, the same ability to address up to 512MB of system RAM, and the same 500MHz core clock speed.
This is probably a disappointment for those of you who were hoping for a true next-generation successor based on ATI's highly successful RV7xx architecture. The Radeon HD 4350 for instance sports twice the stream processors -- 80 -- with eight texture units and 4 ROPs. With the 785G chipset relying on the same 55-nm manufacturing process as the 780G, ATI couldn't affordably fit the 4350's 242 million transistors into their transistor budget for 785G.
As such, 785G's Hybrid Graphics support is limited to the Radeon 3400 series, just like its predecessor the 780G.
Hybrid Graphics isn't going to be a big selling point this time around though. Finding Radeon 3400 cards is becoming increasingly difficult. Newegg for instance only lists three Radeon 3450 boards in stock right now, and two of them are priced higher than the Radeon 4350. Not that it would matter anyway, as one Radeon HD 4350 graphics card is going to run faster than the 780G+Radeon 3450 Hybrid Graphics combination. Radeon 4350 cards start for just $3 more than the cheapest 3450 card on Newegg.
We ran benches with the 785G's integrated graphics and discrete Radeon 4350 graphics card benchmarks for this article so you can see how the two graphics solutions fare against each other.
ATI has added a few new ingredients to the 785G IGP that aren't found in 780G though. For starters, the chip now fully supports DirectX 10.1, whereas 780G was limited to supporting DirectX 10.0. DirectX 10.1 is a pretty incremental improvement over DirectX 10 though, and considering that IGPs don't have the graphics processing horsepower to run DX10 titles anyway it's probably more of a check mark feature for OEMs than anything else.
More notable additions ATI has incorporated into the 785G chipset include HDMI 1.3 support (780G was limited to HDMI 1.2), and RV7xx features like support for hardware video transcoding on the GPU rather than the CPU utilizing ATI Stream, and ATI's Unified Video Decoder 2 (UVD 2); both of these features were first introduced with the Radeon 4000 series of GPUs last year. 785G can also output multi-channel LPCM audio over HDMI as well.
UPDATE 8/5/09: AMD confirmed that multi-channel LPCM audio over HDMI isn't supported by 785G; like 780G the 785G chipset is limited to 2 channels only.
If you recall, UVD 2 includes support for hardware-accelerated picture-in-picture for watching Blu-ray movies, and video enhancement features like dynamic contrast, HD color enhancement (including flesh tones and color vibrance), and post-processing effects like noise reduction, de-interlacing and HD pulldown detection, which is only supported when dynamic contrast is turned off.
So essentially with 785G you could say ATI's fusing the graphics horsepower of RV620 with the video capabilities of RV730. That description isn't completely accurate, but it gives you a quick synopsis of how the new IGP differs from previous ATI offerings. The South Bridge carries over unchanged, with AMD's SB7xx series of chips supported. This is the same chip already in use on current 7-series platforms.
To test the capabilities of the 785G platform out we've got two motherboards from ASUS and Gigabyte. The ASUS board is their M4A785TD-M EVO, while the Gigabyte motherboard used for testing is an engineering sample GA-MA785GPMT-UD2H. We normally don't like to test engineering sample motherboards, preferring to stick with retail samples instead, so instead we'll provide an overview of the product and its current feature set and BIOS. We'll save the more detailed analysis with performance for when we get our hands on a retail sample.