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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Amiga500 - Wednesday, June 25, 2008 - link
Apple has passed over control of Open CL to the Khronos group, which manage open sourced coding.To all intentions and purposes, it is open source. :-)
emergancyexit - Wednesday, June 25, 2008 - link
i hope you do 3x crossfire can do. maybe a 4x 4850 vs 3x GTX 260 just to satisfy us readers for the moment would be lovely!DerekWilson - Wednesday, June 25, 2008 - link
i'm not sure if this is supported out of the box ... ill have to check it out ...emergancyexit - Wednesday, June 25, 2008 - link
i would really like to know what type of performance theese cards could get in an MMO. (and hopefully compare them to some cheaper cards) Games im interested in are some of the newer titles like Age of conan ( i hear it's graphics are great and is a workout for even a 8800 ultra) And Eve-online (thier new graphics engine works cards pretty hard too)MMO's Graphics usually get pretty intesive with some odd 200+ characters flying around shooting fireballs evrywhere with missles sailing through the air in a land of hundreds of monsters as far as the eye can see. it can get pretty demanding on a gameing computer, just as much (if not more) as a hit new title.
for example, on my current Rig i can get around 50FPS steady at 1440x900 but on Eve-Online i get 35 at the most at peacefull times and 20 or even 15 in a large fight with FEW graphics options selected.
MIP - Wednesday, June 25, 2008 - link
Great review, the 4870 looks to be fantastic value. However, we're missing the 'heat and noise' part.skiboysteve - Wednesday, June 25, 2008 - link
Not only do these cards rock, but I wouldn't be surprised if AMD has an ace up its sleeve with the 4870x2... with that crossfire interconnect directly connected to the data hub that you showed on the chart. That and the fact that they have been looking forward to this crossfire strategy of attacking the high end for quite some time so they might have some tricky driver stuff coming with it.I have been disappointed with the heat and power consumption of these cards. But:
1) Someone said powerplay is getting a driver tweak and, I can always clock them lower in 2D than 500/1000 (which is insane for 2d)
2) That hardware site someone linked earlier showed a more than 50% reduction in temperatures with an aftermarket cooler! Thats insane!!
And finally, if I can get the 1 & 2 fixed... I want to know how well these babys overclock. If I can get a 4850 running like a 4870 or better... yum. And in that case, how high will a 4870 OC? And I want to know this with a non stock cooler, because apparently the stock ones suck. With a non stock cooler if the 4850 clocks up to 4870 level, but the 4870 clocks way up too... i'm gonna have to grab a 4870.
So yeah, fix #1 and #2 and find me non-stock cooler OC #s and I'll go buy one (maybe two?) when nehalem comes out
Powered by AMD - Wednesday, June 25, 2008 - link
Impressive review, Thanks :)A few glitches:
It says "Power Consumption, Heat and Noise", but the graphs only shows Power Consuption.
In Page 17 (The Witcher), in second paragraph, it says 390X2 instead of 3870.
Thanks again.
Cheers from Argentina.
Conscript - Wednesday, June 25, 2008 - link
atleast that was the tile of the second to last page...but only see two power consumption graphs?Proteusza - Wednesday, June 25, 2008 - link
I quote one Kristopher Kubricki regarding whether the RV770 is inferior to the GT200:"It is. Even AMD isn't going to tell you otherwise. You can debate this all you want, but it's still a $200 video card."
So, please tell me now why I should pay $650 for a GTX280. I'm struggling to see the logic here.
Source: http://www.dailytech.com/Update+AMD+Preps+Radeon+4...">http://www.dailytech.com/Update+AMD+Pre...50+Launc...
(near the bottom)
AbRASiON - Wednesday, June 25, 2008 - link
I can live with a greedier card than my 8800GT but I refuse to put up with a noisy machine.Any comments on the heat and noise please? would be nice!