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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  • anactoraaron - Wednesday, December 15, 2010 - link

    I would like to thank Ryan for the article that makes me forget the "OC card in the review" debacle. Fantastic in depth review with no real slant to team green or red. Critics go elsewhere please. Reply
  • Hrel - Wednesday, December 15, 2010 - link

    When are you guys gonna put all these cards in bench? Some of them have been out for a relatively long time now and they're still not in bench. Please put them in there. Reply
  • ajlueke - Wednesday, December 15, 2010 - link

    I agree with most of the conclusions I have read here. If you already own a 5800 series card, there isn't really enough here to warrant an upgrade. Some improved features and slightly improved FPS in games doesn't quite give the same upgrade incentive as the 5870 did compared a 4870.
    There are some cool things with the 6900 and 6800 series. Looking at the performance in games, the 6970 and even the 6870 seemed to get much closer to 2X performance when placed in crossfire as compared to 5800 series cards. That is a pretty interesting development. All in all, a good upgrade if you didn't buy a card last generation. If you did, it seems the wait is on for the 28 nm version of the GPU.
    Reply
  • Belard - Wednesday, December 15, 2010 - link

    NO!

    The 800 cards were the HIGH end models since the 3000 series and worked well through to the 5000 series with the 5970 being the "odd one" since the "X2" made more sense like the 4850X2.

    It also allows for a "x900" series if needed.

    AMD needs to NOT COPY Nvidia's naming games... did they hire someone from Nvidia? Even the GeForce 580/570 still belong to the 400 series since its the same tech. SHould have been named 490 and the 475... But hey, in 12 months, Nvidia will be up to the 700 series. Hey, Google Chrome is version 8.0 and its been on the market for about 2 years! WTF?!

    What was their excuse again? Oh, to not create confusion with the 5700 series? So they frack up the whole model names for a mid-range card? The 6800's should have been 6700s, simple as that. Yes, there will be some people who will accidentally downgrade.

    What the new 6000 series has going for AMD is that they are somewhat cheaper and easily cost less to make than the 5000s and what Nvidia makes.

    In the end, the 6000 series is the first dumb-thing AMD has done since the 2000 series, but nowhere near as bad.
    Reply
  • MS - Wednesday, December 15, 2010 - link

    In terms of effienct usage of space though AMD is doing quite well; ... should be efficient

    Nice article so far,

    Regards,
    Michael
    Reply
  • nitrousoxide - Wednesday, December 15, 2010 - link

    The power connector on the left (8-pin of 6970 and 6-pin of 6950) has a corner (bottom left corner) cut down, that's because the cooler doesn't fit with the PCB design, if you install it with force the power connector would get stuck. So the delay of 6900 Series could be due to this issue, AMD needs one month to 'manually polish' all power connectors of the stock-cards in order to go with the cooler. Well, just a joke, but this surely reflects how poorly AMD organizes the whole design and manufacture process :) Reply
  • nitrousoxide - Wednesday, December 15, 2010 - link

    you can find this out here :)
    hiphotos. baidu. com/coreavc/pic/item/70f48d81ffe07cf26d811957. jpg
    Reply
  • nitrousoxide - Wednesday, December 15, 2010 - link

    AMD promises that every one will get a unique 6970 or 6950, different from any other card on the planet :) Reply
  • GummiRaccoon - Wednesday, December 15, 2010 - link

    The performance of these cards is much better with 10.12, why didn't you test it with that? Reply
  • Ryan Smith - Wednesday, December 15, 2010 - link

    10.12 does not support the 6900 series.

    8.79.6.2RC2, dated December 7th, were the absolute latest drivers for the 6900 series at the time of publication.
    Reply

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