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GDDR5 uses an 8-bit prefetch, like GDDR4, but ushers in more innovations. First of all, GDDR5 uses two clock frequencies, CK and WCK, the latter being twice as fast as the former. Commands are transferred in SDR at frequency CK; addresses are transferred in DDR at frequency CK; and finally, data are transferred in DDR and at frequency WCK. In the case of the Radeon HD 4870, which uses GDDR5 at 900MHz, commands are transferred at 900MHz SDR, addresses at 900MHz DDR and data at 1800MHz DDR.
This approach reduces problems related to signal quality during transmission of commands and addresses while enabling very high frequencies for data transmission. Unfortunately, the higher frequencies also mean higher error probability. So to ensure the validity of the data transmitted, GDDR5 implements an error detection mechanism based on the one used by networks. If an error is detected by the memory controller, the command that caused it can be re-executed.
So, AMD and Nvidia have made very different choices in order to meet the bandwidth needs of their GPUs, and those choices are related to their divergent visions of graphics processors. Nvidia, faithful to its concept of enormous monolithic GPUs, could afford to use a 512-bit bus, thus avoiding the supply problems that generally accompany the use of a leading-edge memory technology. Conversely, from the inception of the RV770, AMD has concentrated its efforts on a GPU with a reduced die size for high-end cards. As the AMD engineers told us, the first version of the RV770 was supposed to have no more than 480 ALUs, but the GPU proved to be "pad limited" in that configuration.
Consequently, AMD was able to offer the GPU it just released, with 800 ALUs that are almost “free” in terms of die surface area. It’s a problem Nvidia will face in developing its GT200b using a finer process: how to keep a 512-bit bus on a smaller die without being pad limited. With the preceding generation, Nvidia was forced to abandon the 384-bit bus when it moved from the G80 (0.08µ) to the G92 (0.065µ). So there’s a good chance that will also happen with the 512-bit bus. But this time, Nvidia may rely on GDDR5 to compensate for the loss of bandwidth.
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finally ATI is getting some love
I have the 4950 and it is great
nice review..I wonder why the 4850 can not render race driver : GRID
for the pure gamer at heart, the 4870 seems to be a steal.
however, what are the possibilities for a CUDA like processing environment or handling Physics engines? I think AMD has done a great job making a pure video card, but I believe the future will be with unified technologies of having the GPU assist in other tasks as well.
Time will Tell
Would REALLY help alot if there were charts with these new cards and some of the last gen (what's in the desktop charts now) that way I could
see how much I could gain by upgrading. Maybe thats an update to the desktop charts that just hasnt been dont yet? Seems like it would have already been.
Under load, the heat sink did its job and the temperature didn’t rise all that much – at least not as much as the little Radeon HD 4850.
The 4850 went up 6* and the 4870 went up 10*... I think the 4870 went up more, but you (Tom's) said it went up less.
LOL you don't even have your drivers working properly if a 3870 and 3870x2 are matching each other in performance. Crossfire on the card isn't even working properly, check any bench of a 3870x2 vs 3870 in Call of Duty 4 (ATI preferred drivers).
The real key is what all the prices on these cards are when Nehalem is released.
LOTS of enthusiasts are planning a Nehalem build toward the end of the year. I image they will be getting 4850/4870s or GTX260/GTX280s. All depending on where the prices are I imagine.
Would REALLY help alot if there were charts with these new cards and some of the last gen (what's in the desktop charts now) that way I couldsee how much I could gain by upgrading. Maybe thats an update to the desktop charts that just hasnt been dont yet? Seems like it would have already been.
I agree about the charts. I don't consider buying a 4870 vs an older card like an x1950, but it sure would be nice to see how much it has improved over time.
Thank you ATI. Though I won't be buying your card cause I just bought an 8800 GT maybe this will force nVidia to drop there prices and give me a cheap step up
.
I loved ati since the rage era, im so glad they are back in the game again, i might even consider trading in my 9800gtx sli for a 4850 crossfire down the line, maybe when i setup to ddr3. But for now best bang for the buck cards are the 9800gtx and the 4850 in my opinion
I want either a 48701GB or a 4870X2. I have a 2900Pro 1GB and going to 512MB would not work for me. Plus I wounder if at much higher resolutions if another 512MB would help.
Gawd, I can't wait to get my mits on one of these. I should prolly get my order in now...
I wonder where they tested these cards? My 4850 runs between 52C idle and usually never above 65C while under load. I just use ASUS SmartDoctor which allows you to control the fan speed. Before using smartdoctor the fan speed never changed and it did run at 80C under load.
WTF is going on with those locked minimum clock speeds? I'm already pissed off by HD 3870 running at 300/1126 in XP, what a waste of power! Why don't they offer the possibility to manually (in control panel) underclock the card all the way down to 150-200/300-400 MHz is beyond me.
Finally AM/ATI's on the field. Glad to see the card is performing well esp. given the price. Now all ATI has to do optimize the drivers. Congrats to Toms on a good article written in a while.
Would be interesting if they actually tested these cards on an AMD Platform. Why do that always test AMD parts seperately?
WTF is going on with those locked minimum clock speeds? I'm already pissed off by HD 3870 running at 300/1126 in XP, what a waste of power! Why don't they offer the possibility to manually (in control panel) underclock the card all the way down to 150-200/300-400 MHz is beyond me.
This is because just like underclocking a CPU there is a minimum frequency and a minimum voltage that is needed. Also these are gaming class GPUs aimed at raw power(= more power use + heat)and not really to be energy efficient. Although energy efficiency (usually goes hand in hand with heat output) counts to a certain extent when OCing and higher clock speeds these negatives of lower energy efficiency can be overcome through better HSFs/smaller manufacturing process etc.
Would be interesting if they actually tested these cards on an AMD Platform. Why do that always test AMD parts seperately?
Because the Phenom's aren't very good!
From what Ive heard, the 150 clock is one of the gen clocks on a few of the bios, just not implemented yet. Give it time
Yes, the idle clocks aren't going nearly low enough with the current BIOSs. I've actually seen a BIOS floating around that had the right idle clocks (160/500MHz I think). Hopefully this will be corrected soon.
On a separate note, what's up with RV770 and UE3? I hadn't realized until now that the GeForce cards really pull ahead in those tests. With any other engine it wouldn't be that big a deal, but UE3 is kind of important.