Introduction

The strategy of rebranding current-generation high-end chips as next-generation performance-segment ones worked quite differently for NVIDIA and AMD. NVIDIA designed its previous-generation high-end chip, the GK104, as skillfully as the G92. It is energy efficient, has a relatively low transistor count, only requires eight memory chips to tag along, and can make do with cost-effective VRM designs. AMD's "Tahiti" silicon, in contrast, was built to be a "big" chip, with about 24 percent more transistors than the GK104, a requisite twelve memory chips occupying its wider memory bus, and heftier VRM design requirements. Despite all that, GK104 and Tahiti ultimately powered graphics cards in the same performance segment.

Fast forward to the "next generation," and NVIDIA deployed its big GK110 silicon to power high-end parts, relegating the GK104 to such power performance-segment cards as the GeForce GTX 760 and GTX 770. According to the latest Steam Hardware survey, the GTX 760 is also a highly popular graphics card. It can run any game at 1080p, comes at a sub-$250 price, and is energy-efficient to the extent of not looking out of place in this segment. The same can't be said for "Tahiti." Although it powers the $250-ish Radeon R9 280, it is more expensive to make (lower scope for price-cuts) and has power supply requirements rivaling GPUs two segments above it. With the next-gen 20 nm silicon fab process still out of sight, AMD must definitely be feeling the pinch of selling a 4.3 billion transistor GPU with 12 memory chips, complex VRM, and heavy coolers for under $250, so their efforts into looking for a solution don't come as a surprise. Enter "Tonga."



AMD's new "Tonga" silicon continues to be built on the 28 nm process, but is aimed at weeding out all the shortcomings which make "Tahiti" seem out of place in this market segment. It has as much (if not higher) shading power and room for higher clocks, but a narrower memory interface, lower transistor count, and more efficient implementation of the Graphics CoreNext architecture. The idea behind "Tonga," hence, is to power graphics cards that offer nearly the same performance as the R9 280 and R9 280X, but with less power consumed, lighter cooling solutions, simpler VRM, and greater room for price-cuts. The first card based on this chip is the Radeon R9 285, which we're reviewing today. The R9 285 doesn't have all the shaders of the Tonga silicon enabled (indicated by the red area in the architecture diagram above). At $250 and with factory overclocked cards coming at $10-$20 premiums, the R9 285 is designed to compete with NVIDIA's GeForce GTX 760 at not just raw performance, but also energy-efficiency and noise.

The Radeon R9 285, by virtue of its naming, is designed to replace the Radeon R9 280 from AMD's product stack (which has been declared end-of-life). It has 1,792 stream processors, 112 TMUs, and 32 ROPs, the same as the R9 280, but a narrower 256-bit wide GDDR5 memory interface with less memory, 2 GB. One can expect some AMD add-in board partners to come up with 4 GB non-reference R9 285 cards. While the GPU is clocked at 918 MHz, the memory is clocked to run at 5.50 GHz (GDDR5-effective), working out to 176 GB/s of memory bandwidth. It's worth noting here that "Tonga" uses a newer version of the Graphics CoreNext architecture. It is supposed to provide higher performance per clock than "Tahiti," and offers many of the features "Hawaii" (the chip that powers the R9 290 series) and "Bonaire" (R7 260X) introduced, including XDMA CrossFire (no more CrossFire bridge cables needed), TrueAudio DSP (our kettle is whistling), and the ability to build 4-display Eyefinity setups using all four display connectors on the card.



The specific card we're reviewing today is the Sapphire Radeon R9 285 Dual-X OC, a factory-overclocked implementation by AMD's leading AIB partner that offers overclocked speeds of 965 MHz on the core and 5.60 GHz on the memory. Its most striking feature is the Dual-X cooling solution, which may not win beauty contests, but earned the reputation of being one of the quietest VGA cooling solutions on the market. Sapphire used something similar to tame its Tahiti-based R9 280, so we're optimistic about the cooling solution on this card.