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
Dear girls and guys,does anyone know of a manufacturer, who offers a HD4850 with a better cooler? I'm desperately searching for one...
Please reply!
Graven Image - Wednesday, June 25, 2008 - link
Asus recently announced a 4850 with a non-stock cooler, though their version still doesn't expel the air out the back like a dual slot design. (http://www.asus.com/news_show.aspx?id=11871)">http://www.asus.com/news_show.aspx?id=11871). Its not available yet thought. My guess is mid-July we'll probably start seeing a couple different fan and heatsink designs.strikeback03 - Thursday, June 26, 2008 - link
Only dual-slot card I've ever used was an EVGA 8800GTS 640, it sucked air in the back and blew it into the case.Final Destination II - Wednesday, June 25, 2008 - link
Nice! 7°C cooler, that's a start! I guess I'll wait a bit more, then.Spacecomber - Wednesday, June 25, 2008 - link
Although I'm somewhat dubious about dual card solutions, I keep looking at the benchmarks and then at the prices for a couple of 8800 GTs.Perhaps, if the 4870 forces Nvidia to reduce their prices for the GTX 260 and the GTX 280, they will likewise bring down the price for the 9800 GX2. This is already the fastest single card solution, and it sells for less than the GTX 280. If this card starts selling for under $400 (maybe around $350), will this become Nvidia's best answer to the 4870?
Given the performance and the prices for the 4870 and the 9800 GX2 will Nvidia be able to price the GTX 280 competitively, or will it simply be vanity product - ridiculously priced and produced only in very small numbers?
It should be interesting to see where the prices for video cards end up over the course of the next few weeks.
kelmerp - Wednesday, June 25, 2008 - link
Better HD knickknacks? Better offloading/upscaling?chizow - Wednesday, June 25, 2008 - link
The HD4000 series have better HDMI sound support with 8ch LPCM over HDMI, but still can't pass uncompressed bistreams. Image quality hasn't changed as there isn't really any room to improve.kelmerp - Wednesday, June 25, 2008 - link
It would be nice to have a video card, where it doesn't matter how weak the current-gen processor is (say the lowliest celeron available), the card can still output 1080p HDTV without dropping any frames.Chaser - Wednesday, June 25, 2008 - link
Good to have back at the FRONT of the finish line.JPForums - Wednesday, June 25, 2008 - link
Ragarding the SLI scaling in Witcher:The GTX 280 SLI setup may be running into a bottleneck or driver issues, rather than seeing inherent scaling issues. Consider, the 9800 GTX+ SLI setup scales from 22.9 to 44.5. So the scaling isn't an inherent SLI scaling problem. Though it may point to scaling issues specific to the GTX 280, it is more likely that the problem lies elsewhere. I do, however, agree with your general statement that when CF is working properly, it tends to scale better. In my systems, it seems to require less CPU overhead.