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AMD Pitcairn With 768 Shaders: What is This Mystery Chip?

By - Source: Tom's Hardware DE | B 37 comments

Tom's Hardware Germany got its hands on a prototype of a AFOX HD 7850, the world's first single-slot board with this chip, which ended up being more than meets the eye. Is it an unannounced GPU, or something that was never meant to ever leave the lab?

Our colleagues at one of our European labs were handed an early version of an AMD Pitcairn-based Radeon HD 7850. What made this AFOX unit special from the currently existing Radeon HD 7850 reference design that we've already peeled apart is that is it a single-slot solution as opposed to one that takes up two of your expansion spaces. Here is what comes up with plugging it into GPU-Z:

A look at the device ID, the clock speeds and memory reveal nothing out of the ordinary. What caught our attention, however, was the number of available shader units. While the Radeon HD 7850 we were expecting comes with 1024 shaders, our sample had only 768 shaders.

This compelled us to dig deeper, so we removed the cooler and the abundant amounts of thermal paste. The board itself was produced by AOLIDA, Jiutan Xinhua Town (Guangdong).

Please keep in mind that this is just an engineering sample, and is not a fair representation of any final shipping product. Any product packing a Radeon HD 7850 GPU will obviously be equipped with 1024 shaders. We're treating this product as something of a mystery in the Tom's Hardware labs.

We tried looking into the BIOS to see if it would shed some light on the unexpected number of shaders, but none of our traditional BIOS tools revealed any information. The card identified itself as a Radeon HD 7850 in AMD's current Catalyst driver suite software, but it was incompatible with the Overdrive overclocking functions.

BIOS limitation, laser-cut or faulty chip?

With a card that identifies itself (somewhat) as a Radeon HD 7850, we were expecting a chip stamped with the batch number 1151, like all of the other HD 7850 and 7870 chips so far, but scrubbing the GPU revealed 1152 ENG as the batch number, further confusing the matter. If it is indeed a different chip, then perhaps it isn't a case of cut or BIOS-disabled shaders. In fact, even after attempting to flash the reference firmware of an HD 7870 and an HD 7850, the card was both stable and exhibited no change in performance, leading us to assume that it truly only packs 768 shaders.

We've brought this issue to AMD only to be referred back to the board partners. AFOX told use that this chip belonged to a batch of GPUs AMD delivered in March 2012 for layout and design purposes. Still, we're not sure how this 768-shader GPU ended up on the board designated for the HD 7850, pre-production sample or not.

One theory is that AMD is sending out partially defective chips for PCB developers to experiment with instead of throwing them away, but that may go against the logic of having engineers trying to validate on an 'incomplete' GPU. Maybe - just maybe - it's an unannounced Radeon HD 7830 that slipped through the cracks and into our labs.

Our team in Germany will be putting this card through its paces. Stay tuned for that coming next week!

Update 05/03/2012

AMD Shanghai became aware of our discovery of a Pitcairn chip with 768 shaders and made it clear that it wasn't especially happy about us spreading news of a Radeon HD 7850 with only 768 shaders. To be clear, AFOX was just as surprised as everyone else to learn about this mystery chip. The PCB with our mystery chip was produced at the beginning of the Radeon HD 7800-series' production run. It's plausible that these 768-shader chips were indeed for validation due to supply considerations. Given the stir that this discovery has created, it's safe to assume that this chip wasn't intended to leave the engineering labs.

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Top Comments
  • 38 Hide
    ScrewySqrl , May 3, 2012 2:53 PM
    almost too bad...
    there's a market for the 768-shader chip of a 7830 somewhere around $180, filling the gap between 7770 ($130) and 7850 ($230), replacing the old 6850/6870 and competing with the 560/560ti
  • 26 Hide
    ctbaars , May 3, 2012 2:56 PM
    I look for single slot solutions. Maybe AMD's next success.
  • 23 Hide
    EzioAs , May 3, 2012 3:30 PM
    Quote:
    almost too bad...
    there's a market for the 768-shader chip of a 7830 somewhere around $180, filling the gap between 7770 ($130) and 7850 ($230), replacing the old 6850/6870 and competing with the 560/560ti


    Agreed. And with nvidia not releasing mid range cards for some time now, they could have the best solution for $200 and lower which is a great sweet spot for gamers in that budget
Other Comments
    Display all 37 comments.
  • 23 Hide
    monsta , May 3, 2012 2:52 PM
    CSI Shanghai
  • 38 Hide
    ScrewySqrl , May 3, 2012 2:53 PM
    almost too bad...
    there's a market for the 768-shader chip of a 7830 somewhere around $180, filling the gap between 7770 ($130) and 7850 ($230), replacing the old 6850/6870 and competing with the 560/560ti
  • 26 Hide
    ctbaars , May 3, 2012 2:56 PM
    I look for single slot solutions. Maybe AMD's next success.
  • 4 Hide
    osamabinrobot , May 3, 2012 3:14 PM
    im very interested in finding out how these perform heat wise. especially if i can drop two into my box in crossfire without there being like 1/2" between them for better air flow to knock back that almost automatic 10 degree jump in temp on the top card.
  • 23 Hide
    fulle , May 3, 2012 3:26 PM
    I was also hoping it was something filling the gap between the 7770 and 7850. A 768 shader Pitcairn could potentially be a near perfect HTPC card too. Enough performance to do some gaming, single slot solution, really low power consumption....
  • 23 Hide
    EzioAs , May 3, 2012 3:30 PM
    Quote:
    almost too bad...
    there's a market for the 768-shader chip of a 7830 somewhere around $180, filling the gap between 7770 ($130) and 7850 ($230), replacing the old 6850/6870 and competing with the 560/560ti


    Agreed. And with nvidia not releasing mid range cards for some time now, they could have the best solution for $200 and lower which is a great sweet spot for gamers in that budget
  • 21 Hide
    ern88 , May 3, 2012 4:08 PM
    7830 anyone!!!
  • 21 Hide
    fuzznarf , May 3, 2012 4:08 PM
    edvinasmCall it whatever you want, unless it works with Adobe Creative Suite (which it won't as it's not Cuda architecture) it is irrelevant for anything but games. IMO...

    wrong! CS6 supports OpenCL.
  • 17 Hide
    semisonic , May 3, 2012 4:11 PM
    Maybe it's related to the design chip for the new Xbox or PS4?
  • 14 Hide
    frombehind , May 3, 2012 4:36 PM
    semisonicMaybe it's related to the design chip for the new Xbox or PS4?


    Maybe... But that does not explain the clearly PC-form-factor of this card, or the PC type connections.

    Looks like a pet project that AMD decided not to pursue for whatever reason...

    Although a single slot card of that kind of power does sound kinda cool.
  • 13 Hide
    de5_Roy , May 3, 2012 4:47 PM
    7830 or 7790? i thought 7790 would be a bit less powerful than this.
    ba 7830 would be nice. there's a big gap between 7770 and 7850 that needs to be filled.
    with nvidia facing supply issues and (afaik) no midrange kepler in sight... amd stands to make quite a bit of money at that segment. 7800 cards already offer very good performance in their class.
  • 8 Hide
    eddieroolz , May 3, 2012 5:30 PM
    An incomplete board is not always the best thing to be using for validation, since it might behave differently from the complete board. In either case though, I think we just ruined AMD's 7830 launch party.
  • 4 Hide
    Anonymous , May 3, 2012 6:06 PM
    They do have a gap, and this surfacing sure gets the speculation going for a 7830 or 7790.
  • 16 Hide
    cobra5000 , May 3, 2012 6:14 PM
    aftcometIs "Pitcairn" another word for irrelevant?

    No, but aftcomet is.
  • 2 Hide
    alidan , May 3, 2012 6:53 PM
    i would love a single slot "gameing" solution...
    i dont need the best of the best, in fact i turn down shadows in every game reguardless of when it was made just because it gives me that much more headroom.
    if i could put this instead of a 2 slot i would get it.
  • 2 Hide
    blazorthon , May 3, 2012 7:03 PM
    There're several gaps in performance between the GCN cards. The 7750 and 7770 have a large gap (7750 performs on par with the 6750, but the 7770 is right next to the 6850). The 7770 and the 7850 have a large gap (the 7770 is right with the 6850 the 7850 is between the 6950 2GB and the 6970). A 7830 would solve one of these gaps and it would do so very nicely. I doubt that the other gaps will be filled, but that's me.
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