Power Consumption
It doesn’t take a Ph.D. to realize AMD has succeeded in bringing the performance, but what about power consumption. As a member of the Evergreen family we have some high expectations on the conifer-inspired Cypress GPU. When we looked at the specifications we saw that AMD had specified a pretty high maximal power consumption, but when idle the card would consume as little as 27W. Time to investigate.
AMD has made wonders with the RV870 GPU when it comes to power consumption when the card is idle. A complete system with Intel’s Core i7-965 processor and the fastest card on the market consume on average 150W when idle. Only GeForce GTX 285 is close while the rest ruin the chart with their high numbers. This is in spite of 2.15 billion transistors being used.
Under heavy load in the Furmark graphics benchmark power consumption rises, a lot, but Radeon HD 5870 does consume less than 4870X2 and GTX295, which it also beats in many benchmarks. Even GTX 285 consume more power and this is a much slower card.
RV870 strangles clock frequencies and voltages
If we once again return to power consumption when idle there is a very simple explanation to the substantially lower consumption. As we mentioned earlier in the article when we discussed the memory controller, which now has a lot better control over the GDDR5 memories. This means that the card, when the load decreases, not only lowers clock frequencies of both GPU and memory, but also the voltages for both components. And this is clearly reflected in the numbers shown above.
 |
||
|---|---|---|
| Clock frequency at load (MHz) | Clock frequency when idle (MHz) |
|
| HD 4890 | 850/975 | 157/975 |
| HD 5870 | 850/1200 | 157/300 |
| HD 4870X2 | 750/900 | 507/500 |
| GTX285 | 670/1242 | 300/100 |
| GTX295 | 576/999 | 300/100 |
Graphics cards are starting operate more and more like CPUs, which is about freaking time. We look forward to seeing what the mid-range and budget cards of the Evergreen family can do lower power consumption even further.
