AMD Radeon HD 7970 Launch Review

Product: AMD Radeon HD 7970 Video Card
Company: AMD
Author: James Prior
Editor: Charles Oliver
Date: December 24th, 2011

Power & Temperature

AMD introduced a new feature for their GPUs with this generation, using technology developed for the mobility space - Bus Alive, Chip Off. BACO, as we brought to you here, is the ability to have the GPU power down to insignificant amounts of power while idle. The Cypress and Cayman boards have low idle consumption relative to their load power, around 20W, achieved through dropping voltages and clock speeds. Tahiti introduces a greater than 95% reduction in idle power vs. full performance power, by shutting down the GPU.

The ZeroCore Power state is enabled at screen display blank, with the fan off for zero noise. Now you can leave your gaming PC on overnight with the display blank enabled, if you want to keep your steam/origin/itunes/torrent downloads going.

This ability extends to Crossfire, where additional GPUs are sent to sleep when no work is being done on those second, third or fourth GPUs. This has obvious advantages for APU based systems using dual graphics, as well as performance desktops. Even with modern applications leveraging GPU compute, they may not leverage multiple GPUs to accelerate their work; second cards maybe idle and sucking wind, using power for no reason. With ZeroCore Power those GPUs can turn off, even as you edit photos and videos in your GPU accelerated apps.

AMD has also continued their use of PowerTune, technology that analyzes the board workload requirements at a ~100ms polling interval. As workloads turn on different amounts of transistors, the clockspeeds can be varied to ensure thermal limits are not exceeded. This in turn allows for the base clock rate to be increased so more workloads can run closer to the TDP maximum set by the board. AMD does not yet have Turbo Core technology for PowerTune, where lower power workloads can automatically be increased in performance by increasing the board clocks. However, the downclocking is very fine and offers multiple p-states where engine clock can varied by small amounts to keep performance as optimal as possible for the thermal load.

AMD also equipped the Radeon HD 7970 with a new fan, which runs at reduced RPM to lower noise. Traditionally this means less airflow, so the fins are specially shaped for more air movement, and the fan is larger than previously seen. In addition, the heatsink is a new vapor chamber design and is mounted using the same phase-change thermal interface material (TIM) as seen on the Radeon HD 6990, for better heat conduction. The single-slot display output configuration also allows for full slot exhaust once more, which will also help lower temperatures and permit lower fan speeds, reducing noise. The dust shroud is removable without requiring the heatsink to be dismounted from the board, for easier cleaning.

In operation the cooler works well, keeping the GPU away from the high 80s and low 90s temperatures that get enthusiasts worried while gaming. The noise levels are pretty high before the driver kicks in; whisper quiet at boot it is not. However inside a case you won't hear it spin up unless you're in an extended gaming session and the whole room is hot from your stanky fragging session. It's on par with the GTX 580 cooler in terms of noise level and intrusiveness under load, and an improvement over the 5800 and 6900 series reference coolers.

For future reference designs, AMD should consider looking into dual fan style heatsinks as preferred by enthusiasts everywhere. There's a reason why all the AIBs deliver these custom models, it's not just because they look cool - they are cool; cooler running, better overclocking headroom and longer lasting, which is exactly what the ultra enthusiast market wants.

We recorded GPU core temperature via GPUz to record peak and minimum temperatures during testing. The results are below:

We recorded system power draw during testing of different workloads. Idle is with the Windows 7 balance power plan and display blank screen saver engaged, media is during playback of an AVC-encoded 1080p video in CyberLink PowerDVD 10 with AMD/CUDA accelerated TrueTheater, and Load is the peak power reading taken during 3DMark11 GPU Test 2 at extreme preset. The results are below: