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.
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.