AMD Radeon R9 285X “Tonga XT” Graphics Card Reportedly Features 2048 SPs, 384-Bit Bus and 3 GB GDDR5 VRAM


According to a report published by Fudzilla, AMD's Radeon R9 285X graphics card which features the fully enabled Tonga XT GPU will launch in September. The Radeon R9 285X will be powered by the Tonga GPU featured in AMD's upcoming FirePro W7100 and Radeon R9 285 graphics cards featuring lower power draw compared to previous generation Tahiti core while being faster in terms of performance.AMD Tonga Radeon R9 285X

AMD Radeon R9 285X "Tonga XT" Graphics Card Reportedly Features 2048 SPs, 384-Bit Bus

When I saw the AIB made Radeon R9 285 that leaked lasat week, I mentioned that the cards featured a lower tier heatsinks compared to the Radeon R9 280 and Radeon R9 280X graphics cards which made me doubt their overall performance but from the recent FirePro W7100 launch, it seems like AMD has indeed made some gains in process design optimization which is the reason why the Tonga GPU ends up consuming way lesser power than the Tahiti Pro and Tahiti XT variants we have seen over the last two years. For comparison, the recently released FirePro W7100 has a sub-150W TDP while Tahiti Pro featured on the FirePro W8000 has a 225W TDP with the Radeon R9 280 "Tahiti Pro" featuring a TDP of 250W due to higher clock speeds. I am not comparing the W7100 with the W7000 since that was based off the Pitcairn core which isn't a direct comparison to the specifications reported for the Tonga GPU.

The specifications of the Tonga GPU have been confirmed and we have already seen block diagram of the Pro variant just a few hours ago which confirm that the Radeon R9 285 will feature 1792 stream processors configured in 28 compute units. Based on the GCN 1.1 die, the Tonga GPU has 32 Compute Units in total but we are looking at a toned down version which has four CUs disabled resulting in the 1792 SPs variant. The Tonga GPU has 4 triangles per clock cycle, 32 ROPs, 112 TMUs, L2 cache of 512/1024 KB and a 256-bit memory controller. The Radeon R9 285 features a 4 GB GDDR5 memory running across a 256-bit bus pumping out a cumulative bandwidth of 176 GB/s since its clocked at 1375 MHz . The Tonga GPU was always meant to be highly efficient and AMD has toned down its TDP to sub-150W so we can say a TDP of 150W is what’s to expect from the consumer Radeon R9 285 variant which goes on sale this month.

From the block diagram comparison posted by Hardware.Fr, we can see that the Tonga GPU houses eight ACE (Asynchronous Compute Units) compared to just two on Tahiti and each shader engine has its own geometry processor and a rasterizer unit which houses 8 Compute Units per block. The Tonga Pro variant has two of these CUs disabled resulting in 1792 stream processors. The Multimedia accelerators block has been updated with the XDMA CrossFire engine and addition of TrueAudio DSPs which deliver the TrueAudio tech. Last we can see a large L2 cache, part of which is blacked out which points that this model doesn’t feature the full core but it does have a larger cache compared to Tahiti which may tell why the card is less resilient to bandwidth.

But the most interesting news comes from Fudzilla that the Radeon R9 285X which is the reported name for the Tonga XT based variants features the full 32 CU die which includes 2048 stream processors, 32 ROPs and 128 TMUs. We don't have any specifics regarding the clock speeds, even the ones reported for the Radeon R9 285 are based off factory overclocked variants so we can't be so sure but 918 MHz is what's being said the reference clock for Radeon R9 285 so we can expect something around 933 MHz+ for the Tonga XT variant. What's weird is that the Radeon R9 285X is allegedly featuring a 384-bit memory bus compared to 256-bit bus on its Pro variant and also includes a higher VRAM updated from 2 GB to 3 GB.

The Radeon R9 285 is already considered a mid-tier board from its looks and design but the Radeon R9 285X could be a decent update over Radeon R9 280X' Being similar to Tahiti in board design but the updated core with new architecture will leverage the performance and while the Tahiti XT variants have a TDP of 250W, we can see a sub 200W TDP for Tonga XT variants which arrive in September as reported by the source. The pricing for the Radeon R9 285 could fall in between $250 US while the Radeon R9 285X could retail at $300 US since Tahiti XT and Tahiti Pro based cards have already received major price cuts during the last few months. Do note that the specifications for the Tonga Pro and the 32 CU full die for Tonga XT is more or less confirmed however we can't say for sure whether the 384-bit bus bit seems legit. We have to wait a bit to confirm this.

AMD Tonga Pro and Tonga XT Block Diagram Comparisons:AMD Tonga XT Block DiagramAMD Tonga Block Diagram

AMD Radeon R9 285 “Tonga” Specification Sheet”:

AMD Radeon R7 260X AMD Radeon R9 270 AMD Radeon R9 270X AMD Radeon R9 280 AMD Radeon R9 280X AMD Radeon R9 285 AMD Radeon R9 285X AMD Radeon R9 290 AMD Radeon R9 290X AMD Radeon R9 295X
AMD Radeon R9 295X2
GPU Core Neptune XT Curacao Pro Curacao XT Tahiti Pro Tahiti XT Tonga Pro Tonga XT Hawaii Pro Hawaii XT Hawaii XTX Vesuvius
GPU Process 28nm 28nm 28nm 28nm 28nm 28nm 28nm 28nm 28nm 28nm 28nm
GPU Cores 896 1280 1280 1792 2048 1792 2048 2560 2816 2816 5632
Core Clock 1100 MHz 900 MHz 975 MHz 933 MHz 1000 MHz 918 MHz TBA 947 MHz 1000 MHz ~1100 MHz 1018
Memory Clock 1625 MHz 1400 MHz 1400 MHz 1250 MHz 1500 MHz 1375
1250 MHz 1250 MHz ~1250 MHz 1250 MHz
Memory Bus 128-bit 256-bit 256-bit 384-bit 384-bit 256-bit 384-bit? 512-bit 512-bit 512-bit 512-bitx2
Memory Bandwidth 104.0 GB/s 179.2 GB/s 179.2 GB/s 224.4 GB/s 288.0 GB/s 176.2 GB/s 288.0 GB/s? 320 GB/s 320 GB/s 320 GB/s 320 GB/s x 2
TMUs / ROPs 56 / 16 80 / 32 80 / 32 116 / 32 128 / 32 112 / 32 128 / 32 160 / 64 176 / 64 176 / 64 176 / 64 x 2