Cayman: The Last 32nm Castaway

With the launch of the Barts GPU and the 6800 series, we touched on the fact that AMD was counting on the 32nm process to give them a half-node shrink to take them in to 2011. When TSMC fell behind schedule on the 40nm process, and then the 32nm process before canceling it outright, AMD had to start moving on plans for a new generation of 40nm products instead.

The 32nm predecessor of Barts was among the earlier projects to be sent to 40nm. This was due to the fact that before 32nm was even canceled, TSMC’s pricing was going to make 32nm more expensive per transistor than 40nm, a problem for a mid-range part where AMD has specific margins they’d like to hit. Had Barts been made on the 32nm process as projected, it would have been more expensive to make than on the 40nm process, even though the 32nm version would be smaller. Thus 32nm was uneconomical for gaming GPUs, and Barts was moved to the 40nm process.

Cayman on the other hand was going to be a high-end part. Certainly being uneconomical is undesirable, but high-end parts carry high margins, especially if they can be sold in the professional market as compute products (just ask NVIDIA). As such, while Barts went to 40nm, Cayman’s predecessor stayed on the 32nm process until the very end. The Cayman team did begin planning to move back to 40nm before TSMC officially canceled the 32nm process, but if AMD had a choice at the time they would have rather had Cayman on the 32nm process.

As a result the Cayman we’re seeing today is not what AMD originally envisioned as a 32nm part. AMD won’t tell us everything that they had to give up to create the 40nm Cayman (there has to be a few surprises for 28nm) but we do know a few things. First and foremost was size; AMD’s small die strategy is not dead, but getting the boot from the 32nm process does take the wind out of it. At 389mm2 Cayman is the largest AMD GPU since the disastrous R600, and well off the sub-300mm2 size that the small die strategy dictates. In terms of efficient usage of space though AMD is doing quite well; Cayman has 2.64 billion transistors, 500mil more than Cypress. AMD was able to pack 29% more transistors in only 16% more space.

Even then, just reaching that die size is a compromise between features and production costs. AMD didn’t simply settle for a larger GPU, but they had to give up some things to keep it from being even larger. SIMDs were on the chopping block; 32nm Cayman would have had more SIMDs for more performance. Features were also lost, and this is where AMD is keeping mum. We know PCI Express 3.0 functionality was scheduled for the 32nm part, where AMD had to give up their PCIe 3.0 controller for a smaller 2.1 controller to make up for their die size difference. This in all honesty may have worked out better for them: PCIe 3.0 ended up being delayed until November, so suitable motherboards are still at least months away.

The end result is that Cayman as we know it is a compromise to make it happen on 40nm. AMD got their new VLIW4 architecture, but they had to give up performance and an unknown number of features to get there. On the flip side this will make 28nm all the more interesting, as we’ll get to see many of the features that were supposed to make it for 2010 but never arrived.

Refresher: The 6800 Series’ New Features VLIW4: Finding the Balance Between TLP, ILP, and Everything Else
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  • DoktorSleepless - Wednesday, December 15, 2010 - link

    What benchmark or game is used to measure noise? Reply
  • Hrel - Wednesday, December 15, 2010 - link

    I'm not 100% but I believe they test it under Crysis. It was either that or a benchmark that put full load on the system. It was in an article in last year or 2, I've been reading so long it's all starting to mesh together; chronologically. But suffice it to say it stresses the system. Reply
  • Hrel - Wednesday, December 15, 2010 - link

    It's furmark, it's in the article. Reply
  • Adul - Wednesday, December 15, 2010 - link

    nice Christmas gift from the GF :D Reply
  • AstroGuardian - Wednesday, December 15, 2010 - link

    I saw my GF buying a couple of those. One is supposed to be for me and she doesn't play games...... WTF? Reply
  • MeanBruce - Wednesday, December 15, 2010 - link

    Wow, you are getting a couple of 6950s? All I am getting from my 22yo gf is a couple of size F yammos lying on a long narrow torso, and a single ASUS 6850. Don't know which I like better, hmmmmm. Wednesday morning comic relief. Reply
  • Adul - Wednesday, December 15, 2010 - link

    damn sounds good to me :) enjoy both ;) Reply
  • SirGCal - Wednesday, December 15, 2010 - link

    I'm happy to see these power values! I did expect a bit more performance but once I get one, I'll benchmark it myself. By then the drivers will likely have changed the situation. Now to get Santa my wish list... :-) If it was only that easy... Reply
  • mac2j - Wednesday, December 15, 2010 - link

    One of the most impressive elements here is that you can get 2x6950 for ~$100 more than a single 580. That's some incredible performance for $600 which is not unheard of as the price point for a top single-slot card.

    Second... the scaling of the 6950 combined with the somwhat lower power consumption relative to the 570 bodes well for AMD with the 6990. My guess is they can deliver a top performing dual-GPU card with under a 425-watt TDP .... the 570 is a great single chip performer but getting it into a dual-gpu card under 450-500w is going to be a real challenge.

    Anyway exciting stuff all-around - there will be a lot of heavy-hitting GPU options available for really very fair prices....
    Reply
  • StormyParis - Wednesday, December 15, 2010 - link

    It's nice to have all current cards listed, and helps determine which one to buy. My question, and the one people ask me, is rather "is it worth upgrading now". Which depends on a lot of things (CPU, RAM...), but, above all, on comparative perf between current cards and cards 1-2-3 generations out. I currently use a 4850. How much faster would a 6850 or 6950 be ? Reply

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