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As with the Radeon HD 4870 X2 and Nvidia’s second-generation GeForce GTX 295, ATI’s Radeon HD 5970 populates a single PCB. It consists of two 2.15 billion transistor Cypress GPUs with 1GB of GDDR5 memory each, joined by a 48-lane PLX PCI Express bridge. The bridge is, for the most part, the same one seen on last-generation’s Radeon HD 4870 X2. However, it has been updated for PCI Express 2.1, an incremental and non-performance-related evolution.
|Radeon HD 5970||Radeon HD 5870||Radeon HD 5850|
|Total Transistors||4.3 billion||2.15 billion||2.15 billion|
|Shader Processors||2 x 1,600||1,600||1,440|
|Engine Clock Rate||725 MHz||850 MHz||725 MHz|
|Memory Clock Rate||1,000 MHz||1,200 MHz||1,000 MHz|
|Memory Bandwidth||2 x 128 GB/s||153.6 GB/s||128 GB/s|
|Texture Units||2 x 80||80||72|
|Texture Fillrate||116 GTexel/s||68 GTexel/s||52.2 GTexel/s|
|ROPs||2 x 32||32||32|
|Pixel Fillrate||46.4 GPixel/s||27.2 GPixel/s||23.2 GPixel/s|
|Compute Performance||4.64 TFLOPs||2.72 TFLOPs||2.09 TFLOPs|
|Maximum Board Power||294W||188W||170W|
|Idle Board Power||42W||27W||27W|
Each of the two graphics processors is fully-featured, with 1,600 shader processors (ALUs), 80 texture units, 32 ROPs, and 1GB of attached GDDR5 memory on a 256-bit bus. What is changed are the core and memory clocks. The pair of Cypress chips runs at 725 MHz and the memory at 1 GHz. Thus, at stock clocks, we’d expect the Radeon HD 5970 to be the fastest single discrete card in ATI’s stable, but slower than two Radeon HD 5870s in CrossFire.
But the shipping clocks don’t tell the whole story, according to ATI.
Why Not Go All-Out?
Much of the board’s length can be attributed to the onboard power circuitry needed to drive the two Cypress GPUs. Here’s where many of the design decisions behind this card were actually made.
For example, ATI reduced the voltages it used and correspondingly dropped the 5970’s clock rates to Radeon HD 5850 levels. This was done to keep maximum board power to 294W—under the defined 300W PCI-SIG electromechanical specification, delivered through the physical slot (75W), one six-pin auxiliary connection (another 75W), and an eight-pin auxiliary connector (150W). Pushing Radeon HD 5870 frequencies (850 MHz core/1,200 MHz memory) would have pushed max. board power closer to 375-400W and immediately cut out a segment of enthusiasts who don’t have twin eight-pin auxiliary power connectors on their power supplies.
However, ATI says the Radeon HD 5970 was designed to run at those clock rates. It features specially-screened low-leakage ASICs that run cooler than higher-leakage parts. It employs 5 Gb/s GDDR5 memory actually rated for 1,250 MHz. And perhaps most important, its vapor chamber-based cooling solution is designed with enough capacity to dissipate as much as 400W.
The only missing piece is an official voltage tweaking utility. In an unprecedented move by a GPU vendor, ATI went so far as to provide us with such a utility—a reference app—to give us access to those elevated settings. According to the rep who briefed us, third-party board vendors will bundle their own voltage apps along with hardware so that those with capable-enough PSUs will get the chance to push the hardware a little further—at least to 5870 levels, we’re hoping.
That’s A Huge Board
Those of you who thought the Radeon HD 5870 was already “healthy”-sized, this 5970 is even larger—an inch longer, to be exact. Despite the increase in length, the board’s exterior isn’t much different from what you saw on the Radeon HD 5870—the same fully-shrouded red/black motif with faux rear-vents are still in effect. Because ATI kept power down under 300W, it gets away with one six-pin and one eight-pin auxiliary connector on the board’s top-edge. There’s a single CrossFire connector, should the holiday season treat you well and you want to spend $1,200 on graphics cards.
Perhaps most notable is the rear I/O bracket. Gone is the HDMI output connector (you’d have to be crazy to tie this card into an HTPC). Instead, ATI exposes two dual-link DVI outputs and a single mini-DisplayPort output. Thus, Eyefinity is still viable here, right up to 3 x 2560x1600.
ATI uses the space freed up by the smaller DisplayPort and missing HDMI outputs for a full-length exhaust vent. While there’s ventilation all along the top of the board, most of the card’s heated air exits the back. In contrast, the Radeon HD 5870 is far guiltier of re-circulating hot air.