Single page Print

AMD's Radeon R9 285 graphics card reviewed


Tonga is quite the surprise
— 7:00 AM on September 2, 2014

As a guy who reviews video cards, it's pretty easy to become cynical about these things. That's been especially true during the past couple of years, as we've seen the same handful of graphics chips spun into multiple "generations" of products. The core GPU technology is a technological wonder, but the endless re-spins get to be tiresome.

When AMD revealed the imminent arrival of the Radeon R9 285 recently, I have to admit, I wasn't exactly thrilled. Yes, the R9 285 would be based on a new chip, code-named Tonga, but that chip just looked to be a cost-reduced and slightly tweaked variant of existing silicon—not quite the stuff of legend.

The Radeon R9 285 by the numbers
Heck, have a look at the specs for the Radeon R9 285 versus the card it replaces, and you'll see what I mean.

GPU
boost
clock
(MHz)
ROP
pixels/
clock
Textures
filtered/
clock
Shader
processors
Memory
interface
width
(bits)
Memory
transfer
rate
Board
power
Starting
price
Radeon R9 280 933 32 112 1792 384 5 GT/s 250W $279
Radeon R9 285 918 32 112 1792 256 5.5 GT/s 190W $249
Radeon R9 280X 1000 32 128 2048 384 6 GT/s 250W $299

In terms of key specs, the principal change from the Radeon R9 280 to the R9 285 is the move from a 384-bit memory interface to a 256-bit one. The narrower interface should make the R9 285 cheaper to produce, but it will also mean less memory bandwidth—and memory bandwidth is one of the primary performance constraints in today's graphics cards. Aside from the reduction in memory throughput, the R9 285 appears to be very similar to the R9 280 card that it replaces (and to the Radeon HD 7950 that came before it and was essentially the same thing.)

Ho-hum.

Worse, the $249 starting price for the R9 285 doesn't seem like much of a bargain, given that the R9 280 is going for $219 at online retailers right now, presumably while they close out stock to make room for the new card. That all felt like kind of a raw deal, frankly. What could AMD be thinking?

My, uh, lack of enthusiasm was dampened somewhat when the first example of the R9 285 arrived in Damage Labs. Behold the MSI Radeon R9 285 Gaming OC Edition:


This puppy is gorgeous, and its twin-fan cooler performs as well as its looks suggest. There's good news on the performance front, too, since MSI has cranked up the Boost clock to 973MHz, 55MHz above stock.

At least MSI was doing good work with its part of the equation.

Still, I thought, a snazzy cooler and paint job couldn't fix the basic problem with the R9 285. Although the new Radeon was up to snuff elsewhere, its memory bandwidth just looked a bit anemic.

Peak pixel
fill rate
(Gpixels/s)
Peak
bilinear
filtering
int8/fp16
(Gtexels/s)
Peak
shader
arithmetic
rate
(tflops)
Peak
rasterization
rate
(Gtris/s)
Memory
bandwidth
(GB/s)
Radeon R9 280 30 104/52 3.3 1.9 240
Radeon R9 285 29 103/51 3.3 3.7 176
Radeon R9 280X 32 128/64 4.1 2.0 288
GeForce GTX 760 33 99/99 2.4 4.1 192
GeForce GTX 770 35 139/139 3.3 4.3 224

The MSI card's higher boost clocks would give it a bit more oomph in some categories than the stock numbers shown for the R9 285 above, but it wouldn't do anything to address the biggest issue. The R9 285's 176 GB/s of memory bandwidth is just a lot less than the R9 280's 240 GB/s—and quite a bit less than what the competing GeForces have to offer, too.

Tonga's dilemma
So you can understand my reticence. Tonga looked to be nothing more than a dreary re-spin of AMD's existing technology, based on the same Radeon DNA as the Hawaii GPU introduced one year ago—and the Bonaire chip first outed in March of 2013. Those chips weren't that different from the Tahiti GPU that debuted at the end of 2011.

To be fair, AMD did make some notable improvements in Hawaii and Bonaire. Both of those chips have the TrueAudio DSP block onboard, so that games can offload audio processing to a dedicated hardware unit on the GPU. Those chips include a new XDMA data transfer mechanism for CrossFire, which allows frame data to be transferred via PCI Express instead of over an external bridge. Hawaii and Bonaire also have updated display outputs with support for the latest DisplayPort standards.

In fact, AMD tells us that only Radeon cards based on Bonaire, Hawaii, and Tonga will support the variable refresh displays being enabled by its Project FreeSync initiative. I wasn't aware that older Radeons would be excluded, but apparently they will.

One other addition in Hawaii—and now Tonga—is a smarter version of AMD's PowerTune dynamic voltage and frequency scaling (DVFS) scheme. The new PowerTune monitors the GPU's current state constantly and makes fine-grained adjustments to clock speeds and supplied voltages in order to keep the GPU within its pre-defined thermal and power peaks. The smarter PowerTune algorithm allows the graphics chip to squeeze out every ounce of performance possible within those limits.

These tweaks are all well and good, and Hawaii in particular is a truly impressive GPU specimen, but they don't do that much to improve the GPU's fundamental performance or efficiency. Hawaii gets its potency from sheer scale more than anything else.

That reality was a problem for Tonga, in my view, because Maxwell is coming. Nvidia has already released a small-scale version of its new GPU architecture aboard the GeForce GTX 750 Ti, and we know the little Maxwell is about twice as power-efficient as the corresponding chip based on the Kepler architecture. Nvidia is widely rumored to be prepping larger Maxwell derivatives for release soon. Those chips are likely to convert this architecture's increased power efficiency directly into higher performance. If Tonga were just a cost-reduced Tahiti chip with TrueAudio added, AMD could be in for a world of hurt.