The Radeon HD 4850 & 4870: AMD Wins at $199 and $299
by Anand Lal Shimpi & Derek Wilson on June 25, 2008 12:00 AM EST- Posted in
- GPUs
One, er, Hub to Rule them All?
With R500 AMD introduced its first ring bus, a high speed, high bandwidth bus designed to move tons of data between consumers of memory bandwidth and the memory controllers themselves. The R600 GPU saw an updated version of the ring bus, capable of moving 100GB/s of data internally:
On R600 the ring bus consisted of two 512-bit links for true bi-directional operation (data could be sent either way along the bus) and delivered a total of 100GB/s of internal bandwidth. The ring bus was a monster and it was something that AMD was incredibly proud of, however in the quest for better performance per watt, AMD had to rid itself of the ring and replace it with a more conventional switched hub architecture:
With the ring bus data needed to be forwarded from one ring stop to the next and all clients got access to the full bandwidth, regardless of whether or not they needed it. For relatively low bandwidth data (e.g. UVD2 and display controller data), the ring bus was a horrible waste of power.
With the RV770 all that exists is a simple switched hub, which means that sending data to the display controller, PCIe and UVD2 (AMD's video decode engine) traffic are now far less costly from a power standpoint. Another side effect of ditching the ring bus is a reduction in latency since data is sent point to point rather than around a ring. With the move to a hub, AMD increased their internal bus width to 2kbits wide (which is huge). Maximum bandwidth has increased to 192GB/s (in 4870) but this depends on clock speeds.
With nearly double the internal bandwidth and a point to point communication system, latency between memory clients should be decreased, and huge amounts of data can move between parts of the chip. Certainly getting enough data on to the GPU to feed 800 execution units is a major undertaking and AMD needed to make a lot of things wider to accommodate this.
The CrossFire Sideport
Although AMD isn't talking about it now, the CrossFire Sideport is a new feature of the RV770 architecture that isn't in use on the RV770 at all. In future, single-card, multi-GPU solutions (*cough* R700) this interface will be used to communicate between adjacent GPUs - in theory allowing for better scaling with CrossFire. We'll be able to test this shortly as AMD is quickly readying its dual-GPU RV770 card under the R700 codename.
One thing is for sure, anything AMD can do to assist in providing more reliable consistent scaling with CrossFire will go a long way to help them move past some of the road blocks they currently have with respect to competing in the high end space. We're excited to see if this really makes a difference, as currently CrossFire is performed the same way it always has been: by combining the output of the rendered framebuffer of two cards. Adding some sort of real GPU-to-GPU communication might help sort out some of their issues.
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jALLAD - Wednesday, July 9, 2008 - link
well I am looking forward to a single card setup. SLI or CF is beyond the reach of my pockets. :PGrantman - Friday, July 4, 2008 - link
Thank you very much for including the 8800gt sli figures in your benchmarks. I created an account especially so I could thank Anand Lal Shimpi & Derek Wilson as I have found no other review site including 8800gt sli info. It is very interesting to see the much cheaper 8800gt sli solution beating the gtx 280 on several occasions.Grantman - Friday, July 4, 2008 - link
When I mentioned "no other review site including 8800gt sli info" I naturally meant in comparison with the gtx280, gx2 4850 crossfire etc etc.Thanks again.
ohodownload - Wednesday, July 2, 2008 - link
computer-hardware-zone.blogspot.com/2008/07/ati-radeon-hd4870-x2-specification.tml
DucBertus - Wednesday, July 2, 2008 - link
Hi,Nice article. Could you please add the amount of graphics memory on the cards to the "The Test" page of the article. The amount of memory matters for the performance and (not unimportant) the price of the cards...
Cheers, DucBertus.
hybrid2d4x4 - Sunday, June 29, 2008 - link
Hello!Long-time reader here that finally decided to make an account. First off, thanks for the great review Anand and Derek, and hats off to you guys for following up to the comments on here.
One thing that I was hoping to see mentioned in the power consumption section is if AMD has by any chance implemented their PowerXpress feature into this generation (where the discrete card can be turned off when not needed in favor of the more efficient on-board video- ie: HD3200)? I recall reading that the 780G was supposed to support this kind of functionality, but I guess it got overlooked. Have you guys heard if AMD intends to bring it back (maybe in their 780GX or other upcoming chipsets)? It'd be a shame if they didn't, seeing as how they were probably the first to bring it up and integrate it into their mobile solutions, and now even nVidia has their own version of it (Hybrid Power, as part of HybridSLI) on the desktop...
AcornArmy - Sunday, June 29, 2008 - link
I honestly don't understand what Nvidia was thinking with the GTX 200 series, at least at their current prices. Several of Nvidia's own cards are better buys. Right now, you can find a 9800 GX2 at Pricewatch for almost $180 less than a GTX 280, and it'll perform as well as the 280 in almost all cases and occasionally beat the hell out of it. You can SLI two 8800 GTs for less than half the price and come close in performance.There really doesn't seem to be any point in even shipping the 280 or 260 at their current prices. The only people who'll buy them are those who don't do any research before they buy a video card, and if someone's that foolish they deserve to get screwed.
CJBTech - Sunday, June 29, 2008 - link
Hey iamap, with the current release of HD 4870 cards, all of the manufacturers are using the reference ATI design, so they should all be pretty much identical. It boils down to individual manufacturer's warranty and support. Sapphire, VisionTek, and Powercolor have all been great for me over the years, VisionTek is offering a lifetime warranty on these cards. I've had poor experiences with HIS and Diamond, but probably wouldn't hesitate to get one of these from either of those manufactures on this particular card (or the HD 4850) because they are the same card, ATI reference.Paladin1211 - Saturday, June 28, 2008 - link
Now that the large monolithic, underperforming chip is out, leaving AMD free to grab market share, I'm so excited at what to happen. As nVidia's strategy goes, they're now scaling down the chip. But pardon me, cut the GTX 280 in half and then prices it at $324.99? That sounds so crazy!Anyone remembers the shock treatment of AMD with codename "Thunder"? DAAMIT has just opened "a can of whoop ass" on nVidia!
helldrell666 - Friday, June 27, 2008 - link
Anand tech why didnt you use and amd 790FX board to bench the radeon cards instead of using an nvidia board for both nvidia and ATI cards.It would be more accurate to bench those cards on compatible boards .I think those cards would have worked better on an amd board based on the radeon express 790fx chipset.