AMD: Southern Islands (7*** series) Speculation/ Rumour Thread

it probably have same amount of L2 Cache that would explain the missing transistors..
according to CV CF numbers, 7850 should be faster than 6870 and 7870 more or less 6970..

 

The memory speed is a bit surprising. Pitcairn appears to be roughly equal (maybe even a tad superior) to Cayman, but has significantly lower bandwidth. I wonder what motivated that choice… perhaps power? I suppose caching and memory controller improvements might alleviate that, we'll see.

 

Targeted die-size?

btw.
7950: 200W maximum board power
7870: ~175W typical board power

Could be HD 7870 real world consumption above HD 7950?

 

Do you mean that it would have allowed AMD to use a smaller PHY on Pitcairn? I guess that's possible, but I'm not sure how much of an impact this would have had, given that the memory clock gap between Pitcairn and Tahiti is about 13%.

I think typical and maximum power really mean the same thing in this case, i.e. maximum power with default PowerTune settings.

 

Sharp eyes.
Will be interesting to see actual test results, it may well draw more than the HD7950, as you say.

 

->@->

Performance : 2560 GFlops
DP Performance : 160 (320?) GFlops

 

Speaking of that, I think the chip should be rather small (below 250mm²), if that's 2xCV.

AMD didn't give a number for Typical Board Power for HD7950, but for HD7970 it was 210W (compared to 250W Max Board Power). So keeping similar ratios between Typical and Maximum for HD7950, I'd say the 7870 should draw about the same. We'll see how that turns out in practice.

That speculated 0.5MB of L2 cache difference is only good for ~24 million transistors (ok probably a bit more), not ~200 million. Though granted the transistor count numbers may use generous rounding.

Just based on specs I would say it should be a bit faster than that. The 7850 should imho beat a 6950, with the 7870 ending up between gtx570 and gtx580.
(A 7950 has 40% more CUs, the 7870 has 25% higher clock, which turns out to be a 12% advantage for the 7950 in the shader department - but from that angle I would actually think the 7870 is probably at least as fast due to scaling better with clock. The 7950 though has 54% more memory bandwidth which should give it a ~15% advantage.)
Interesting to note that the 7950 (and 7970 too) have nearly twice the memory bandwidth per theoretical ROP throughput than the 7870...

 

im quite impressed, 114W card performance around GTX580

http://www.forum-3dcenter.org/vbulletin/showpost.php?p=9193514&postcount=195

 

Later on in that thread with more games added the result isn't as good. Looks like it's strong in DX11 just like Cape Verde, but similarly loses pace in DX9.

edit: This is the performance summary in that thread. Which looks to include BFBC2, Crysis Warhead, Dirt3, Dragon Age 2, ME2, Metro2033, Starcraft 2

100%= 7970
580 88.3%
7950 85.1%
6970 77.7%
570 75.9%
560TI 448 73%
7870 72.9%
6950 68.7%
560Ti 64%
7850 60.8%
560 58%
6780 56.5%

 

These scores are right around my predictions. I guess I was too optimistic though, in that thread they also have overall performance scores and there the 7850/7870 did quite a bit worse (the 7850 below 6950, the 7870 below 6970), strange.

 

If it holds up that it does best in most demanding games though since it does really well in BF3/Crysis 2, who cares if it gets 100 FPS instead of 140 in a bunch of DX9 old games.

I already figured it would be ~6970. Each shader in GCN is honestly about =to a shader in VLIW4/5 (will do better in newer/tess games, but overall)

So 1280 SP's at 1ghz is pretty easy to peg as somewhere around 6970. Somewhat fewer SP's at a higher clock.

 

7870 is 16% slower than 6970 with 12% lower texture/compute power.. lack of bandwidth ?
and 29% faster than 6870 with 26% higher compute power and 58% texture fillrate..

 

I think this depends also by the resolution and AA levels tested, as in higher resolutions the Bandwidth could be more and more a limiting factor. As Pitcairn is 2x Cape Verde in almost every aspect, I'd expect not less that 60-80% more performance than 7700.

 

VR-Zones take: http://chinese.vr-zone.com/11249/amd-hd7870-hd7850-03032012/

Maybe someone can find more than 20 CUs on Pitcairn. And also the die-size can be measured, if the dies are in scale.

 

Photoshop tells me they are not in scale in that slide.

 

Whats the rumoured release date, 8th March correct?

If you're bored and have nothing else to do, could you scale and check it against Tahiti's die size and Cape Verde's die size separately? At least we'll have something to speculate on (However flawed it is )

 

some more info on the 7800 series (hope this hasnt already been posted)
http://www.3dcenter.org/news/die-spezifikationen-zur-amd-radeon-hd-7800-serie

 

from AMD benchmarking guide..



EDIT:


http://www.3dcenter.org/news/erste-benchmarks-zu-radeon-hd-7850-7870

 

they choose 570/560ti to compare against, are they priced to compete against those cards ?