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
POST A COMMENT

56 Comments

View All Comments

  • gigahertz20 - Monday, July 14, 2008 - link

    AMD needs to get on the ball with their drivers, they still don't even have the 4850 and 4870 listed on their site under video card drivers.

    http://ati.amd.com/support/driver.html">http://ati.amd.com/support/driver.html

    Seems like all their effort was put into just releasing the hardware to sell and make money, and not putting as much time into perfecting the drivers as they should be.
    Reply
  • docmilo - Wednesday, July 16, 2008 - link

    This hotfix is a new set of drivers for the 4800 series. I installed them last night on my 4850 and when I run the Overdrive I reach 700mhz on the gpu stable.
    Reply
  • docmilo - Wednesday, July 16, 2008 - link

    Well the link didn't work. Here's the address:

    http://support.ati.com/ics/support/default.asp?dep...">http://support.ati.com/ics/support/defa...mp;task=...
    Reply
  • Lerianis - Monday, July 14, 2008 - link

    They probably haven't released a new driver for these cards yet and expect you to use the driver they include on the disk with the card. Wait until next month, they will most likely finally have a driver on their website for these cards. Reply
  • alzg22 - Monday, July 14, 2008 - link

    They do have drivers, Catalyst 8.6 introduced support for the 4800 series. It's just not listed under the driver finder, probably. Reply
  • bob4432 - Monday, July 14, 2008 - link

    i think they are referring to a driver that changes the fan speed so you don't cook the 4850/4870s.... Reply
  • KikassAssassin - Monday, July 14, 2008 - link

    You can do that now by creating an Overdrive profile in the control center, and editing the profile's file (Documents/username/AppData/Local/ATI/ACE/profilename.xml) in Notepad. There's a line in there for fan speed that you can edit. I set mine to 40% (up from the default 20%) and idle temps on my 4870 dropped from about 75C to 45C, and load temps dropped from about 95C to about 65C. 40% fan speed was right about at the upper limit I could set it to before the fan noise became annoying (the thing seriously sounds like a freaking jet engine at max speed).

    It'd be nice if they'd add an option to change the fan speed in the control center, though.
    Reply
  • sc3252 - Monday, July 14, 2008 - link

    This card is hot for a $500 video card. I cant wait to pick one up. Two questions I have. Does it actually share the memory or is it separate? Did they fix the stutter associated with Crossfire? Reply
  • DerekWilson - Monday, July 14, 2008 - link

    oh yeah, and we're going to wait until the card actually comes out to look at things like micro-stutter etc... Reply
  • DerekWilson - Monday, July 14, 2008 - link

    memory is not shared. shared framebuffer won't come out for a while yet apparently ...

    each GPU has a separate 512MB framebuffer.
    Reply

Log in

Don't have an account? Sign up now