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790GX: Dissected

AMD 790GX: RV610 For Enthusiasts?
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The 790GX consists of two components (versus Nvidia’s single-chip platforms) : the 790GX northbridge and an SB750 southbridge.

790GX : A Little of This, A Little of That

From the top-down, chipset diagram view, there’s actually very little distinguishing the 790GX northbridge from the 780G that came before it. Both components support HyperTransport 3 connectivity to AMD’s latest processors (790GX runs at up to 2.6 GHz). They both incorporate dual, independent display controllers — one digital and one analog. Support for DVI, HDMI, and DisplayPort are shared between the pair. And the two include onboard graphics based on AMD’s RV610 core.

However, one noticeable difference is PCI Express connectivity. Both chipsets boast a x16 PCIe 2.0 link for graphics. But while the 780G takes a single add-in card, 790GX is able to branch off into a pair of x8 links, offering the same 8 GB/s per slot you’d get from a first-gen x16 connection.

The flexible PCIe configuration lets 790GX boast CrossFireX support for higher-end gaming, similar to what Nvidia did with 780a SLI, which begs the questions, “How many enthusiasts need integrated graphics on their gaming machine” and “How many mainstream gamers need a pair of x16 slots for dual-card setups ?” Aren’t the 790FX and 780G chipsets already doing a great job keeping those respective segments satisfied ?

Fortunately, 790GX offers more than just a divisible PCIe link. The integrated RV610 core, armed with 40 stream processors, the same UVD support, and a 16-bit memory interface gets accelerated from 500 MHz on 780G to 700 MHz on 790GX — exciting since the northbridge is manufactured using the same 55 nm process used to etch 780G. Then again, AMD always did seem confident in the core’s available headroom. As a result of its higher clock, the graphics solution is now being called Radeon HD 3300-class.

Moreover, the side-port memory feature made available to board vendors before (but was rarely used) looks like it’s turning into a standard feature. As a refresher, side-port memory is a DDR2/DDR3 cache that lives on the motherboard, directly connected to the graphics core. Without the memory, the RV610 core utilizes the HyperTransport interface to access DDR2 memory attached to the processor’s integrated controller. But by adding even just 128 MB of DDR3 running at 1,333 MHz, AMD claims performance jumps by as much as 15 percent. We’ll be putting those claims to the test in a performance suite brand new to Tom’s Hardware.

Northbridge
AMD 790GX AMD 780G Nvidia GeForce 8300
Processor Interface HT 3.0/5,200 MT/s HT 3.0/5,200 MT/s HT 3.0/5,200 MT/s
PCI Express Support 2.0/26 lanes/2x8 Graphics 2.0/26 lanes/1x16 Graphics 2.0/19 lanes/1x16 Graphics
Integrated Core RV610 RV610 G86
DirectX/OpenGL 10.0/2.0 10.0/2.0 10.0/2.0
Graphics Clock 700 MHz 500 MHz 500 MHz
Display Outputs DisplayPort, HDMI, DVI, VGA DisplayPort, HDMI, DVI, VGA HDMI, DVI, VGA
Multi-GPU Hybrid CrossFireX, CrossFireX Hybrid CrossFireX GeForce Boost
Addtl. PCIe Six x1 PCIe 2.0 Six x1 PCIe 2.0 Three x1 PCIe 2.0
Southbridge SB750 SB700 N/A
Interconnect A-Link Xpress (4 x PCIe 1.1) A-Link Xpress (4 x PCIe 1.1) N/A
RAID Support RAID 0, 1, 10, 5 RAID 0, 1, 10 RAID 0, 1, 10, 5
Audio HD Audio HD Audio HD Audio
USB 12 USB 2.0 + 2 USB 1.1 12 USB 2.0 + 2 USB 1.1 12 USB 2.0
Ethernet N/A N/A Gigabit Ethernet


Beyond the core’s 3D capabilities, 790GX retains the same video capabilities introduced with 780G. Mainly, it boasts the first-gen Avivo HD display pipeline, including AMD’s Universal Video Decoder. Even if you don’t install a discrete card, the integrated core’s UVD handles Blu-ray playback with ease. To that end, HDCP support is of course an important part of the package and, like AMD’s add-in boards, the Radeon HD 3300’s HDMI output does S/PDIF audio as well. It simply lacks some of the functionality introduced with the RV770 core : acceleration of dual video streams, dynamic contrast, and 7.1-channel audio over HDMI.

As with 780G, 790GX offers two independent display controllers ; one analog (VGA) and the other digital (dual-link DVI, HDMI, or DisplayPort). In all frankness, we would have liked to see two digital outputs this time around. After all, if a gamer is flush enough to afford two cards in CrossFire, he probably has a couple of LCDs, too. Given the scarcity of DisplayPort-equipped displays, expect most 790GX boards to include VGA, DVI, and HDMI outputs, just like we saw with 780G.

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  • 6 Hide
    kitsilencer , August 6, 2008 4:47 AM
    Great review, and it's good to see that AMD is at last able to target more enthusiast markets competitively.
  • 0 Hide
    cangelini , August 6, 2008 5:38 AM
    kitsilencerGreat review, and it's good to see that AMD is at last able to target more enthusiast markets competitively.


    Thanks for the feedback Kit.
  • 1 Hide
    eklipz330 , August 6, 2008 6:19 AM
    ^^^iseriously thought that was sarcasm, until i saw the authors name
  • 0 Hide
    waffle911 , August 6, 2008 7:01 AM
    So... why does a page 15 and 16 of this article exist if there is no page 15 or 16 to the article?
    Take a closer look. What happened?
  • 2 Hide
    YYD , August 6, 2008 7:15 AM
    PCMark seems Intel biased, please read this:
    http://arstechnica.com/reviews/hardware/atom-nano-review.ars/6

    Please change this benchmark suite or check if PcMark Vantage is unbiased.
  • 0 Hide
    cangelini , August 6, 2008 7:23 AM
    waffle911So... why does a page 15 and 16 of this article exist if there is no page 15 or 16 to the article?Take a closer look. What happened?


    That was strange. Should be fixed now.
  • 0 Hide
    cangelini , August 6, 2008 7:24 AM
    YYDPCMark seems Intel biased, please read this:http://arstechnica.com/reviews/har [...] view.ars/6Please change this benchmark suite or check if PcMark Vantage is unbiased.


    Fortunately, with no Intel platforms tested, this should be a non-issue for the current situation ;-) In the future, you'll be seeing SYSmark, though.
  • 1 Hide
    Anonymous , August 6, 2008 7:30 AM
    Seems past page 8 or something the links are corrupt.. can't fully read this article and getting error 404 - page not found.
  • 1 Hide
    Anonymous , August 6, 2008 7:32 AM
    .. and now the article seems to be removed even from the main page!?!?!
  • 0 Hide
    cangelini , August 6, 2008 7:51 AM
    lacrits.. and now the article seems to be removed even from the main page!?!?!


    Alright, mystery solved. It's back up, sans the blank page. Thanks for pointing that out lacrits!
  • 2 Hide
    nickchalk , August 6, 2008 9:31 AM
    Hi, i wanted to ask something aout the article.
    why you use 3470 and 8500 for the tests?
    hybrid crossfire and nvidia boost don't work with faster cards?
    is the performance gain not big with 3870 or 9600gt?
    thanks
  • 2 Hide
    cangelini , August 6, 2008 9:36 AM
    Hybrid CrossFireX uses alternate frame rendering, as does GeForce Boost, I believe. As a result, both technologies are best complemented by discrete boards evenly matched to the integrated core. In the case of the GeForce 8300, that'd be an 8500 GT. For the 790GX, AMD recommends the 3470. To spend any more money on discrete graphics for either platform would be a waste of money even if you could use faster cards.
  • 1 Hide
    nickchalk , August 6, 2008 9:42 AM
    thanks for responding so fast.
    so what if i use a 3650 with this board? or why will i buy a quad core and dont spend some more for a 3850?
  • 0 Hide
    cangelini , August 6, 2008 9:54 AM
    Unfortunately, performance won't scale with the 3650. With that said, you'll still see reasonable gaming performance in Hybrid CrossFireX. The beauty of this board is that you CAN drop in a 3850, 3870, 4850, etc. and then add a second one later for CrossFireX.
  • 0 Hide
    zenmaster , August 6, 2008 11:20 AM
    cangeliniUnfortunately, performance won't scale with the 3650. With that said, you'll still see reasonable gaming performance in Hybrid CrossFireX. The beauty of this board is that you CAN drop in a 3850, 3870, 4850, etc. and then add a second one later for CrossFireX.


    Nice Review, However I would like to see how well SLI scales on this board using a 4850 and 4870 vs another AMD Board with full Duel 16x PCIE 2.0 Slots.

    I've seen some other reviews where Dual 8x PCIE 2.0 Slots start having scaling issues on the 4850 at are not seen on the 3800 Series.
  • 1 Hide
    computerfarmer , August 6, 2008 11:20 AM
    Thank you for this excellent article.
    Does the 128mb side-port limit the on board video to that amount of memory? Does this affect Vista Areo?
  • 1 Hide
    jimmysmitty , August 6, 2008 1:13 PM
    Good article. Phenom can finally OC. I wounder if the mobo makers are going to make them with higher quality voltage regulators so it can support the 9850BE and higher across the selection.
  • 1 Hide
    cshorte , August 6, 2008 1:47 PM
    good review,

    i have a question why do you recommend ddr1066 over 800? i thought there wasn't a huge difference.

    also im a bit confused about this 16x, vs. 8x 8x...
    if i use a single card (for now) which motherboard (790g, 790gx) will produce more graphixs capabilities?
  • 1 Hide
    ltcommander_data , August 6, 2008 2:03 PM
    It would have been interesting to see a comparison between the GMA X4500 and the 790GX.

    http://www.hkepc.com/?id=1510&page=5&fs=idn#view

    The GMA X4500 seems to be much faster than the GMA X3500 and within 10-30% of the 780G in actual games. I guess the 790GX was a timely addition and with it being 20% faster than the 780G, that should open up the lead over the GMA X4500 to 30-50%.
  • 1 Hide
    kenyee , August 6, 2008 2:08 PM
    and which of these upcoming 790GX motherboards are microATX?
    The only one I know of is the DFI one...
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