Report: AMD's Tonga-XT GPU To Have 384-Bit Memory Bus

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By Niels Broekhuijsen
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Might AMD's next Tonga-based graphics card come with a 384-bit memory interface?

When the AMD Radeon R9 285 arrived, one of the first thoughts that most of us had was whether AMD would also be building a Tonga-based graphics card with more stream processors. Not too much is known about the so-called R9 285X, and although we have been able to speculate, it's not up until now that some concrete potential information has surfaced. Japanese website PCWatch has posted some details of the fully-enabled Tonga GPU along with a block diagram.

According to the report, a fully-enabled Tonga GPU, which we expect to be called the Tonga XT, carries 2048 stream processors, 128 TMUs and 32 or 48 ROPs, along with two additional 64-bit memory controllers over the Tonga-Pro on the R9 285, giving it a 384-bit memory interface. This suggests that a graphics card featuring the GPU would come with 3 GB of GDDR5 memory.

Image Source: PC Watch

That's where the details end. Unfortunately, we still haven't heard anything official about the R9 285X, nor a second graphics card with a Tonga GPU for that matter, so for the time being all we know is that this rumor says that the fully-enabled Tonga GPU carries 2048 SPs and a 384-bit memory interface. Whether a graphics card with said GPU will be built, or what it will be officially called, remains a mystery.

If AMD does build this graphics card, we would expect it to perform a notch above the Radeon R9 280X (just like the R9 285 performed a notch above the R9 280), while operating at a slightly lower TDP than the R9 280X. That said, we can't be sure about this, as the bigger memory interface might just make the card powerful enough to compete with Nvidia's just-announced GTX 970, so let's not get our hopes up.

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Niels Broekhuijsen
Niels Broekhuijsen

Niels Broekhuijsen is a Contributing Writer for Tom's Hardware US. He reviews cases, water cooling and pc builds.

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29 Comments Comment from the forums
  • pacdrum_88
    AMD has come catching up to do if they're going to be able to compete with Nvidia on the level of the 970 and 980. I've always been an AMD guy, but unless they really get their power usage down and ramp up the performance, things aren't looking so good. If the 285 is what we have to look forward to (Reasonably less power usage but not much performance gained) then I see the future weighing heavily in team green's favor.
    Reply
  • Sakkura
    14278765 said:
    This is particularly interesting because it doesn't often happen that we see GPUs with memory controllers disabled, while disabling sets of shaders is a common practice to facilitate the binning process.
    Except for the GTX 660 Ti, which was GK104 cut down from 256-bit to 192-bit. And the GTX 650 Ti, which was GK106 cut down from 192-bit to 128-bit. And the GTX 570, which was GF110 cut down from 384-bit to 320-bit. And the GTX 560 SE and GTX 555, which were GF114 cut down from 256-bit to 192-bit. And the GTX 470, and the GTX 465, and the GTX 275, and so on...
    Reply
  • kinggremlin
    , it's not up until now that some concrete potential information

    Concrete potential? Isn't that an oxymoron?
    Reply
  • spentshells
    AMD has come catching up to do if they're going to be able to compete with Nvidia on the level of the 970 and 980. I've always been an AMD guy, but unless they really get their power usage down and ramp up the performance, things aren't looking so good. If the 285 is what we have to look forward to (Reasonably less power usage but not much performance gained) then I see the future weighing heavily in team green's favor.

    This will compete with the 970 and that's the point, Notice the 285 vs the 7950 the bus width is slower yet it performs slightly above at stock, those same revisions will go into this core and it will be matched with the additional bus width and shader count which will show well at least beating the 780 while bringing down the power. If they keep it cheaper than the 780 thats how they sell cards. I see this happening or at meeting the 780 but later we will see an xtx version of the tonga core almost like a Ghz card which will at the very least beat and get close to the 970. Likely at a cheaper price than at least the 780.
    Reply
  • Sakkura
    14281748 said:
    This will compete with the 970 and that's the point, Notice the 285 vs the 7950 the bus width is slower yet it performs slightly above at stock, those same revisions will go into this core and it will be matched with the additional bus width and shader count which will show well at least beating the 780 while bringing down the power. If they keep it cheaper than the 780 thats how they sell cards. I see this happening or at meeting the 780 but later we will see an xtx version of the tonga core almost like a Ghz card which will at the very least beat and get close to the 970. Likely at a cheaper price than at least the 780.

    The GTX 780 is being phased out, the 970 is what AMD will be competing with going forward.

    Adding in the remaining shaders for an R9 285X is not going to make it as powerful as the 780, let alone the 970. The 285 is barely ahead of the 280, there's no reason to think the 285X will be much faster than the 280X.

    And I really don't see them adding another version of Tonga later on to reach even higher performance levels. They have Hawaii covering the high-end market, Tonga is basically just a smaller version of Hawaii.
    Reply
  • fuzzion
    So my 780ti is still cutting edge.
    Reply
  • alextheblue
    Well Sakkura you have to look at it this way... the 285 is a smidge faster than the 280 despite having a narrower 256-bit bus and far less memory bandwidth. This is lately thanks to serious compression improvements. So IF the 285X has a full 384-bit bus, it will have roughly the same bandwidth as the 280X, but would still have the improved compression that saved the 285. The potential for big performance increases above the 280X is there.

    However, I personally don't put much stock in this rumor. We'll see, though.
    Reply
  • spentshells
    14282137 said:
    14281748 said:
    This will compete with the 970 and that's the point, Notice the 285 vs the 7950 the bus width is slower yet it performs slightly above at stock, those same revisions will go into this core and it will be matched with the additional bus width and shader count which will show well at least beating the 780 while bringing down the power. If they keep it cheaper than the 780 thats how they sell cards. I see this happening or at meeting the 780 but later we will see an xtx version of the tonga core almost like a Ghz card which will at the very least beat and get close to the 970. Likely at a cheaper price than at least the 780.

    The GTX 780 is being phased out, the 970 is what AMD will be competing with going forward.

    Adding in the remaining shaders for an R9 285X is not going to make it as powerful as the 780, let alone the 970. The 285 is barely ahead of the 280, there's no reason to think the 285X will be much faster than the 280X.

    And I really don't see them adding another version of Tonga later on to reach even higher performance levels. They have Hawaii covering the high-end market, Tonga is basically just a smaller version of Hawaii.

    But it will also get the far larger memory bus and when paired with the revised core and a possible overclock we could see a huge boost. Purely speculation. Interestingly 285 did so well with the 256bit bus.

    I want a 970 in the future but I could be swayed back to AMD with performance with the right price.
    Reply
  • N.Broekhuijsen
    14280072 said:
    Except for the GTX 660 Ti, which was GK104 cut down from 256-bit to 192-bit. And the GTX 650 Ti, which was GK106 cut down from 192-bit to 128-bit. And the GTX 570, which was GF110 cut down from 384-bit to 320-bit. And the GTX 560 SE and GTX 555, which were GF114 cut down from 256-bit to 192-bit. And the GTX 470, and the GTX 465, and the GTX 275, and so on...
    Whoops. But all fixed now.

    Reply
  • somebodyspecial
    Unfortunately NV can hit 1.5ghz on OC, so no chance of catching the 15-20% free if someone wants it and even then power wasn't through the roof. So yeah, AMD has a lot of catching up to do. You won't hit 1.5ghz on tonga without some pretty special cooling I'd guess. NV's chip did it at quite a few places with nothing special and not much voltage to play with on the users part. It would seem AMD's only option here is hacking pricing to stay competitive and that just means another quarterly loss most likely which is definitely bad for a company who is far in debt, and very little cash to fight with. Their R&D dropping over the last 4yrs shows this also. NV now spends more and doesn't make many of the things AMD does (cpus for servers, consoles etc).

    When your enemy outspends you, makes 3-5x more profit per year or quarter, and makes less products, you're in serious trouble. Tonga and maxwell show this R&D spending clearly (same with Intel cpus and R&D - we're about to see the same thing happen in gpus, which sucks).
    Reply