Benchmarking AMD's 768-Shader Pitcairn: Not For Public Consumption

What If A 768-Shader Pitcairn Existed?

In last week’s news story AMD Pitcairn With 768 Shaders: What is This Mystery Chip?, we reported that, while testing a pre-production sample Radeon HD 7850 shipped to us in a rare single-slot form factor, we discovered a mysterious GPU that didn't match the Pitcairn we were expecting. Instead of coming equipped with the usual 1024 shaders, our engineering sample sported only 768 active shader cores.

We made a number of phone calls and exchanged a number of emails with AMD in an attempt to clarify our sample's origin and intention. What we found was that the 768-shader part did not, in fact, represent a piece of silicon destined to drive an upcoming super-secret derivative product. Rather, the GPU was only intended for board partners. It was never meant to go on sale, and it was certainly never supposed to land in our lab.

But if the part wasn't intended to sell or test, what was its purpose? There is a good explanation for its existence. For AMD’s add-in board partners, it is important to get their hands on GPUs as early as possible. Early access allows them to build boards in preparation for a launch. On the other hand, AMD is wary of leaks that would give away the performance profile of its GPUs in a very competitive graphics market. That’s where deliberately-hobbled engineering samples like this one come into play, allowing board partners to start developing their custom implementations with a chip that thermally and electrically simulates the final product. Meanwhile, AMD doesn’t need to worry about the performance attributes of its final effort getting outed by a company with unfettered access to its technology.

There remain a few points for us to clarify, though. When the single-slot Radeon HD 7850 that we tested appears for sale, we're told that it will feature a complete 1024-shader Pitcairn GPU. Obviously, the sample we're testing today isn't indicative of that final production product. To that end, the benchmark results we'll be presenting on the following pages are most easily thought of as experimental. We have a card here that nobody else has. It's properly recognized by AMD's Catalyst driver as a Radeon HD 7800-series board. And it effectively operates as a single-slot piece of hardware. AMD stresses that, at least for now, there are no plans to produce a Pitcairn GPU with a 768-shader configuration. As far as we are concerned, that’s actually too bad, since the benchmark numbers make such a chip a pretty interesting product. Also, judging by the overwhelmingly positive feedback our initial report generated, both on our own sites and around the Web, there is certainly a market for it. As such, this piece isn't a review so much as it's an exploration of a hypothetical component that doesn't exist (though we'd certainly welcome it if it ever did materialize).

Our prototype with the vendor edited out. The final version will sport the 1024 SPs of a full Radeon HD 7850.

But what makes this chip so interesting if it was never meant for public consumption? We don’t want to give too much away, but let’s take Crysis 2 as an example and look at the performance we get when we run the card through our benchmark using some settings that reflect what a board of this price range can be expected to face in real life.

Let's use a 1920x1080 resolution, 16x AF, 2x MSAA, Ultra details, and DirectX 11 mode for our example. A Radeon HD 7850, which can be found on Newegg starting around $250 (ignoring some rebate offers) takes those settings in stride, achieving a comfortable 41 FPS, on average. The next card down in AMD’s current portfolio, Radeon HD 7770, which sells for about $100 less, is not playable under the same load, averaging around 28 FPS. That leaves a gap of 13 FPS and $100 separating playability and disappointment. Doing a bit of math, the halfway-point between the fastest 7700- and entry-level 7800-series SKU gets us a price tag around $200 and a frame rate around 35 FPS. Lo and behold, the engineering sample in our lab comes in at a respectable 36.5 FPS!

AMD insists that there is no product planned in between the Radeon HD 7770 and 7850. The company is adamant that the 768-shader Pitcairn part was only intended for high-level validation and board characterization. And, at the end of the day, this might go down in history as a cool piece of technology that never makes it out of one site's testing lab.

However, we're certainly allowed to have the opinion that AMD has a gap in its line-up that we think it should be filling rather than ceding to the competition without a fight. And that’s why this GPU is so interesting (aside from the benchmark results that enthusiasts like us find fascinating in their own right). The comments on our news report showed that a card based on a chip like this would definitely appeal to gamers on a limited budget that currently can’t find the right card. While it’s not really our job to find and point out business opportunities to the companies whose products we review, we believe this card would find an audience, and we hope AMD takes note and listens to your comments!

Benjamin Kraft
  • woe96
    i want one, that a amazing place in performance and probably only be $200
  • s3anister
    I would never buy this card for myself but I would find myself recommending a 1GB model, like you mentioned, to family and friends. If the price is right AMD could have a great mid range card.
  • wolley74
    while a nice card, the 6850 is incredibly close and nearly $60 cheaper, the only thing is it does consume more power
  • borden5
    oh man that single slot would be really nice for people who wanted small factor rig
  • slomo4sho
    Wouldn't 2 7750s in crossfire perform better than this rig and also consume less power at the ~$200 price point?
  • erraticfocus
    Slomo4shOWouldn't 2 7750s in crossfire perform better than this rig and also consume less power at the ~$200 price point?
    Maybe, depending on your local market, but the single slot and price point is the whole point to this...
  • Say hello to the AMD HD Radeon 7790.
  • pwnorbpwnd
    This card would be an AMAZING pick for an HTPC, Single slot, Low power, 2gb DDR3 for HDTV's, not to say 1gb wouldn't be okay. But really AMD, do it up! All of this positive feedback is great reason to make a crippled 7850!
  • weatherdude
    This card performs great and a 1 GiB version selling at ~$200 would fill in a very large gap in the market. It would only make sense if AMD is cooking up something they'll likely call a 7830 to do just that. I guess though it would differ from this engineering sample if they're so insistent that they aren't bringing it to market. Maybe it'll have less texture units or ROPs.

    Still this card with 1 GiB at ~$200 would be pretty sweet AMD *nudge* *nudge*.
  • Doesn't the 7770 have 40 Texture Units and not 14?