AMD confirms R680 is two chips on one board
- Thread starter nicolasb
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If only it had the 512bit bus... I'm sure it would hit memory bandwidth limits at 900Mhz core.
Based on what?Considering it's still 16 RBEs, I'd be quite surprised if that where the case under 90% of possible scenarios.
Precisely. And with 2.25-2.5GHz GDDR4 to back it up, RV670 is anything but bandwidth-deficient.
Perhaps there's something similar to this going on with the PLX bridge:
But if the PLX has 3 ports, 1 to the slot, 2 for the chips, there's no way the other card could communicate directly via it from the CF bridge?
Slightely OT but if RV670 is anything but bandwidth limited with 72GB/s then what on earth is the use of Xenos having 256GB/s connected to a considerably weaker core?
I don't think the scenarios are even remotely comparable.
He was talking about R600, so I kinda assumed it would be stuck with the order of the day, which if I remember correctly was 1.8Ghz mem?
Maybe I read your post wrong, but the 256GiB/s is between the ROPS/Z-etc and the 10MiB eDRAM. The bandwidth between the eDRAM die and the shader core is 32GiB/s.
Yeah, that happens when I go for a smoke while writing the post, and not checking after writing the end of it
The point being what?Let me put it differently:how BW limited does the 8800GT appear to be under most common scenarios?BW is certainly important, but when you have what to do with it, oversupplying it does about jack to help performance.
Why aren't they comparable? Its a pretty simple comparison.
What makes the Xenos core capable of using 256GB/s while the R670 core cannot use 72GB/s?
Its not a "Xenos is in a console" thing because being in a console doesn't mean you use more bandwidth, if anything it would mean less because its being used more efficiently.
I acknowledge felix's statement about the lack of compression, thats a valid point and if the consensus is that its that, and that alone which is responsible for the disparity then fine. But if its not (and it would be pretty incredible if compression alone could have such a huge effect) then I can only see 2 possibilites:
Xenos cannot use 256GB/s and thus some, or even much of that bandwidth is wasted.
RV670 is bandwidth limited at 72GB/s, at least in some circumstances even at 720p.
No dude. The EDRAM itself was thought out for very particular cases, namely 4X AA and 720p rendering and was planned in such a way as to provide supposedly free AA. For further Xenos detailing ask Jawed because he loves that chip, I haven't really dealt with it much.
Let's ignore the fact that Xenos is a tad more primitive in the way it handles memory communication(the lack of compression techniques and so on). Bear in mind the memory arrangement IT DOES have, with the UMA and its 700MHz only clock. I don't know how many titles currently use tiling/the EDRAM, so how can you evaluate its impact on Xenos, aside from giving a big figure to quote?Not to mention that for the life of me I can't understand how can a valid comparison between a console GPU and a desktop one be made, all things considered.
Care to show me how you determined that Xenos can/cannot use 256GB/s and how RV670 is BW limited at 720p under MOST circumstances?Could it be under some circumstances?Perhaps. Are those common enough?Probably not or there would've been a significant Delta between it and the R600, considering the BW delta that exists and the fact that they're pretty much the same basic architecture, bar some tweaks.
Now you've made me read up on Xenos:http://www.beyond3d.com/content/articles/4/3
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At last--considering the performance of basic blending op's--RV670 in its GDDR4 flavour is bandwidth limited in almost linear manner (read: not even close to its theoretical rate). At 2600MHz for the memory, an HD3870 is measurably faster (~10%) than a 2200MHz 8800GTS-512 board with similar core clocks, concerning the fore mentioned scenario.
No dude. The EDRAM itself was thought out for very particular cases, namely 4X AA and 720p rendering and was planned in such a way as to provide supposedly free AA. For further Xenos detailing ask Jawed because he loves that chip, I haven't really dealt with it much.
Let's ignore the fact that Xenos is a tad more primitive in the way it handles memory communication(the lack of compression techniques and so on). Bear in mind the memory arrangement IT DOES have, with the UMA and its 700MHz only clock. I don't know how many titles currently use tiling/the EDRAM, so how can you evaluate its impact on Xenos, aside from giving a big figure to quote?Not to mention that for the life of me I can't understand how can a valid comparison between a console GPU and a desktop one be made, all things considered.
Care to show me how you determined that Xenos can/cannot use 256GB/s and how RV670 is BW limited at 720p under MOST circumstances?Could it be under some circumstances?Perhaps. Are those common enough?Probably not or there would've been a significant Delta between it and the R600, considering the BW delta that exists and the fact that they're pretty much the same basic architecture, bar some tweaks.
Now you've made me read up on Xenos:http://www.beyond3d.com/content/articles/4/3
I not saying that Xenos can/can't use 256GB/s bandwidth or that RV670 is/isn't bandwidth limited.
I'm saying it can't be both.
Either 72GB/s isn't enough for RV670 or it is, and by extension its enough for Xenos aswell.
Aside from the compression difference and perhaps some other minor efficiency improvements, there's nothing about the Xenos core (that i'm aware of) that makes it likely to consume more bandwidth than RV670. In fact, the exact opposite is true. The fact that Xenos was designed for 720/4xAA only strengthens my point since they are very low settings for RV670 were its even less likely to be bandwidth limited.
Its nothing to do with it being in a console because if there is a situation in a console environment were a chip is bandwidth limited then that same situation can easily translate over to a PC, expecially given how many games on the 360 turn up on the PC. For example, if Lost Planet used 200GB/s on the 360, why would it only need 50GB/s for the same visual result in the PC?
The bottom line is that if RV670 is incapable of using 72GB/s in most situations then so is Xenos. Conversly, if Xenos finds itself regularly eating up well over 72GB/s then so would RV670 (afterall, both are playing mostly the same games with the same visuals).
All this is of course assuming that the compression issue doesn't make up for the large gap.
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