Remember this slide?

The "Scalable design" block we already know about, that's RV770 - we reviewed it last month. The 150W TDP $300 part is the Radeon HD 4870, and the 110W $200 part is the Radeon HD 4850, the two cards that have caused NVIDIA quite a bit of pain already. The smaller $100 part has a name, and a release date, neither of which we can talk about at this point, but it's coming.

Today however, is about the 250W, $500 multi-GPU solution - internally known as R700. Hot on the heels of the Radeon HD 4800 series launch, AMD shipped out ten R700 cards worldwide, attempting to capitalize on the success of the 4800 and showcase the strength of AMD's small-GPU strategy.

We're assuming that AMD will call the R700 based cards the Radeon HD 4870 X2, and based on the chart above we're expecting them to retail above $500 (possibly $549?). Today's article is merely a preview as R700s won't be officially launched for at least another month, but AMD wanted to unveil a bit of what it's cooking.


ATI R700 ATI Radeon HD 4870 ATI Radeon HD 4850 ATI Radeon HD 3870
Stream Processors 800 x 2 800 800 320
Texture Units 40 x 2 40 40 16
ROPs 16 x 2 16 16 16
Core Clock 750MHz 750MHz 625MHz 775MHz+
Memory Clock 900MHz (3600MHz data rate) GDDR5 900MHz (3600MHz data rate) GDDR5 993MHz (1986MHz data rate) GDDR3 1125MHz (2250MHz data rate) GDDR3
Memory Bus Width 256-bit x 2 256-bit 256-bit 256-bit
Frame Buffer 1GB x 2 512MB 512MB 512MB
Transistor Count 956M x 2 956M 956M 666M
Manufacturing Process TSMC 55nm TSMC 55nm TSMC 55nm TSMC 55nm
Price Point > $500 $299 $199 $199

The R700 board is literally made up of two RV770s with a PCI Express switch connecting the two. The clock speeds are identical to the Radeon HD 4870, and memory size per GPU has been doubled to 1GB, which could help in hi res cases with AA enabled. In other words, R700 should perform very much like a pair of 4870s in CrossFire. Or should it?

Building a Better CrossFire

When AMD began talking about no longer building high end hardware using single monolithic GPUs a few weeks back, we let them know that improving CrossFire support would be incredibly important going forward. AMD told us that they are putting a lot into that but also that they have some exciting technology up their sleeves with R700 to help out as well. Unfortunately, we haven't gotten as much detailed information on how it works, but the new technology is GPU to GPU communication.

Until now, CrossFire has done zero GPU to GPU or framebuffer to framebuffer communication. As with the first iteration, each card fully renders the parts of the screen for which it is responsible (be it a whole frame in AFR, the top or bottom half of a screen, or alternating tiles). These results are sent to a combiner where the digital signals are merged and output to the screen. This is the only communication that takes place in CrossFire at the moment. R700 will change that by allowing GPUs to communicate.


RV770 has a CrossFire X Sideport...we assume that the two RV770s on a single R700 board somehow connect Sideports and make fast. AMD hasn't told us how yet.

It is not clear how extensive this communication will be, what information will be shared, or how much bandwidth requirements are increased because of this feature. And while it is a step in the right direction, the holy grail of single-card multi-GPU solutions will be a shared framebuffer. Currently both GPUs need a copy of all textures, geometry, etc., and this is a huge waste of resources. While the R700 has 2GB of RAM on board, it will still be limited in many of the same ways a 1GB RV770 would be as each GPU only has access to half the RAM on the card. Of course, since we don't have a 1GB RV770 yet, this card could show some advantages over the single 4870 regardless of CrossFire.

Regardless of where we want (and need) to see multi-GPU technology get to, R700 is the first part to follow AMD's official change in strategy, and as such it will be very important to establish their place in the market and will need to prove to gamers that they are taking the high end seriously. It's great that single-card multi-GPU solutions are capable of providing high end performance, but when spending the amount of money required to put a high end part in your system, people expect compatibility, reliability, and consistent performance. We can't really talk about how well they pull that off with prerelease hardware and prerelease drivers, but we can't emphasize the importance of this enough. We will certainly be putting the screws to it when the hardware does eventually make it out into the wild.

UPDATE: Our initial publication of this article indicated a 2x 512MB framebuffer for a total of 1GB on board. We have since learned that the R700 we tested has 2GB of RAM total for 2x 1GB framebuffers. This has affected some of our analysis and conclusion. We do apologize for any confusion this may have caused.

The Card
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  • toyota - Monday, July 14, 2008 - link

    I have seen 4 so far plus all the individuals that have personal cards now and they have ALL been 2gb models. like I said earlier ATI doesnt even have a 4870 X2 1gb model in their slides. Reply
  • Alexstarfire - Tuesday, July 15, 2008 - link

    I've become curious as this is like the 4-5th comment I've come across that talks about a 2GB model and a 1GB model. What I'm curious is whether or not you are talking about a 2x2GB model, to make 4GB across 2 cards, or just 2GB in total RAM, because the one on this site has 2GB of RAM total 2x1GB, 4GB across 2 cards.

    I have a feeling many are just getting confused, but I'd like to sk to make sure.
    Reply
  • Lakku - Monday, July 14, 2008 - link

    AMD, you fail! Without even reading the whole article, which I will finish in a sec, that board layout already has me in a tizzy. Are you really going to point the PCI-E 8 and 6 pint connectors facing that way? Maybe because it's so long, but I am not sure I like that idea of having a stiff cable (most PS's these days have sleeved cables) having to be routed that way. Then again, I am flying off half-cocked right now, so (if you live around Austin, TX and listen to 93.7 12 to 1, you'll know I am part of Snatch... so this may just all backfire in my face after I get done reading the article). Reply
  • Lerianis - Monday, July 14, 2008 - link

    Yeah, I have to agree that is a stupid way to point the connectors..... DOWN? They should be pointed towards the wall of the computer, not the bottom of the computer, in order to take into account that most people have a card or three UNDERNEATH those video cards. Reply
  • toyota - Monday, July 14, 2008 - link

    I didnt read through the whole article but why did Anandtech end up with a 1024mb version when EVERYBODY else is getting 2048mb versions? heck even all the ATI slides showed 2048mb for the R700.

    http://www.driverheaven.net/reviews.php?reviewid=5...">http://www.driverheaven.net/reviews.php?reviewid=5...
    http://enthusiast.hardocp.com/article.html?art=MTU...">http://enthusiast.hardocp.com/article.html?art=MTU...
    http://techreport.com/articles.x/15105">http://techreport.com/articles.x/15105
    Reply
  • orionmgomg - Monday, July 14, 2008 - link

    I was wondering the exact same thing.

    Maybe they are going to release even better results with the 2GB version and blow away Nvida!?

    I am a Nvidia Fan Boy - or should I say - who ever gots the biggest guns Fan Boy, so if ATI brings in the meat and potatos, Ill eat em all up.

    PS: I have an ASUS X38 DDR3 with QX9650 & 2 Gigs DDR3 1600 7-7-7-20, and I have been running just 1 EVGA 8800 Ultra Because SLI is not supported with this mobo, so when I upgraded from the 680i I sold my other Ultra...

    But!!!!!!!! This MOBO HAS CrossFIRE!!!

    As almost all other X38/X48 Mobos do! And I have been waiting for a Cross Fire solution that was worthy. If I could just get 2 of the 4870x2 cards in my system for Quad GPU - that would be really nice - give my Dorkfielf 4.0 something to do. LOL

    PS; Also need to upgrade to Vista 64 as a 32 bit OS would not like 4 gigabytes of ram on the video cards, and with 2GBs system memory - may be a problem - plus upgrade ro 4 GBs of course...
    Reply
  • csiszarerik - Tuesday, July 15, 2008 - link

    Hm, reply on your PS: try to install service pack 1 for Vista... my 4 gigs are there... before it was only 3.3 gigs... i have read somewhere that the new core in SP1 supports higher ram amounts... Reply
  • imaheadcase - Monday, July 14, 2008 - link

    Ram on video card means Jack Squat in all but a few games out, even then its not noticeable. A 512meg vs 2gig card means no performance difference if 2 equal cards.

    Reply
  • Lerianis - Monday, July 14, 2008 - link

    It doesn't? That's funny: every single testing place I have seen says that when you have a lot of memory on the card to hold textures and other things, it does help with performance a lot, since they don't have to page things to the hard drive or pull things from the hard drive as often. Reply
  • Alexstarfire - Tuesday, July 15, 2008 - link

    That's if, AND ONLY IF, all the stuff doesn't already fit onto the cards memory. Most of the time you'll run the FPS into the ground before that happens, negating any performance gain you may possibly get. If, however, you happen to find a game where the FPS remains high, like in GRID, then it will help. Course, you'd need quite a big monitor to get a resolution that high, but that's beside the point. Reply

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