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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Final Destination II - Wednesday, June 25, 2008 - link
http://www.techpowerup.com/reviews/Powercolor/HD_4...">http://www.techpowerup.com/reviews/Powercolor/HD_4...Look! Compare the Powercolor vs. the MSI.
Somehow MSI seems to have done a better job with 4dB less.
Final Destination II - Wednesday, June 25, 2008 - link
Try ASUS, 7°C cooler.Justin Case - Wednesday, June 25, 2008 - link
I thought it was only Johan, and it was sort of understandable since he's not a native English speaker, but it seems most Anandtech writers don't know the difference between "its" and "it's"."It's" means "it is" or "it has" (just as "he's" or "she's"). When you're talking about something that belongs to something else, you use "its" (or "his" / "her").
In a sentence such as "RV770 in all it's [sic] glory.", you're clearly not saying "in all it is glory" or "in all it has glory"; you sare saying "in all the glory that belongs to it". So you should use "its", not "it's".
Even if you can't understand the difference (which seems pretty straightforward, but for some reason confuses some people), modern grammar checkers will pick this up 9 times out of 10.
CyberHawk - Thursday, June 26, 2008 - link
I am not a native English speaker, but I am well aware of the difference. I am also sure that reviewers are also ... it's just that - with all this text, we can forgive them, can't we?I have a bachelor of computer science, studying for higher degree, but: I look at the technical side of the article, so I don't even notice the errors :D (although I can tell the difference I simply don't see it while reading)
CyberHawk - Thursday, June 26, 2008 - link
Oh, I forgot: maybe I'm just being too enthusiastic ;)JarredWalton - Wednesday, June 25, 2008 - link
More likely is that with a 10000 word article and four lengthy GPU reviews in two weeks, errors slipped into the text. I know at one point I noticed Derek says "their" instead of "there" as well, and I can assure you that he knows the difference. I know I use Word's grammar checker, but I'm not sure Derek even uses Word sometimes. :)araczynski - Wednesday, June 25, 2008 - link
of the 4850's, slickdeals has posted a sale, between rebate and coupon off...$150 each. can't beat that bang/$ by anything from nvidia.first ati cards that will ever be in my computers since i've started with the voodoo/riva tnt :)
Denithor - Wednesday, June 25, 2008 - link
Page 15: first reference to "GTX 280" should be "GTX 260" instead.Page 19: I think you meant "type" not "time" in this paragraph.
natty1 - Wednesday, June 25, 2008 - link
This review is flawed. It shows greater than 100% scaling for Crossfire 4870 in Call of Duty 4. Why don't they just give us the raw numbers for both single and dual cards in the same scenario? Why use a method that will artificially inflate the Crossfire results?Denithor - Wednesday, June 25, 2008 - link
If you read the comments before yours, you'd see the answer.Experimental error and/or improved scaling for each card versus a single card. Read the earlier comment for more details.