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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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  • Roland00Address - Wednesday, December 15, 2010 - link

    1) The architecture article is something that can be written before hand, or written during benching (if the bench is on a loop). It has very little "cramming" to get out right after a NDA ends. Anand knows this info for a couple of weeks but can't discuss it due to NDAs. Furthermore the reason anandtech is one of the best review sites on the net is the fact they do go into the architecture details. The architecture as well as the performance benchmarks is the reason I come to anandtech instead of other review sites as my first choice.

    2) The spelling and grammar errors is a common thing at anandtech, this is nothing new. That said I can't complain for my spelling and grammar is far worse than Ryan's.

    If you don't like the style of the review go somewhere else.
    Reply
  • Ryan Smith - Wednesday, December 15, 2010 - link

    1) That's only half true. AMD told us the basics about the 6900 series back in October, but I never had full access to the product information (and more importantly the developers) until 1 week ago. So this entire article was brought up from scratch in 1 week.

    It's rare for us to get too much access much earlier than that; the closest thing was the Fermi launch where NVIDIA was willing to talk about the architecture months in advance. Otherwise that's usually a closely held secret in order to keep the competition from having concrete details too soon.
    Reply
  • Dracusis - Wednesday, December 15, 2010 - link

    Neither the AMD 6xxx series or Nvidia's 5xx series have been added. Would like to see how my 4870x2 stack up against this latest generation and weather or not it's worth upgrading. Reply
  • Makaveli - Wednesday, December 15, 2010 - link

    The Canadian pricing on these cards are hilarious.

    Ncix is taking preorder for the 6970 at $474.

    While they sell the 570 for $379.

    Can someone explain to me why I would pay $100 more for the radeon when the 570 gives equal performance?

    Are these retailers that retarded?
    Reply
  • stangflyer - Thursday, December 16, 2010 - link

    They will price the 6950/6970 high for a few days to get the boys that bleed red and have to have the new cards right away to pay top dollar for the card.

    After a week they will probably be about the same price.
    Reply
  • Ryan Smith - Thursday, December 16, 2010 - link

    Bench will be up to date by the start of next week. Reply
  • Paladin1211 - Thursday, December 16, 2010 - link

    Whats wrong with you rarson? Do you even know whats the difference between "Graphics card review", "Performance review", "Performance Preview"? I dont know how good your grammar and spelling are, but they dont matter as long as you cant understand the basic meaning of the words.

    Most of the sites will tell you about WHAT, but here at AnandTech, you'll truly find out WHY and HOW. Well, of course, you can always go elsewhere try to read some numbers instead of words.

    Keep up the good works, Ryan.
    Reply
  • Belard - Thursday, December 16, 2010 - link

    The 3870 and 3850 were the TOP end for ATI, as was the 4800 and the 5800. Their relationship of model numbers do not have anything to do with the status of Nvidia.

    When the 3870 was brand new, what was the HIGHEST end card ATI had back then? Oh yeah, the 3870!

    4800 is over the 3870, easily.
    4600 replaced the 3800

    The 5800s replaces the 4800s... easily.
    the 5700s kind of replaced the 4800s.

    The 6800s replaces the 5700 & 5800s, the 6900s replace the 5800s, but not so much on performance.

    I paid $90 for my 4670 and a much better value than the $220 3870 since both cards perform almost the same.
    Reply
  • AmdInside - Thursday, December 16, 2010 - link

    I can't think of a single website that has better hardware reviews, at least for computer technology than Anandtech. Ryan, keep up the great work. Reply
  • George.Zhang - Thursday, December 16, 2010 - link

    BTW, HD6950 looks great and affordable for me. Reply

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