Energy And Efficiency
Against our own advice, we used a 1000 W power supply in today’s four-way SLI tests. How much power did we really need?
Manufacture-specified TDP aside, it appears that our power supply actually needed 282 W per GeForce GTX 480 graphics card. Yet, pushing our power supply beyond its rated limit caused the four-way configuration to pull 1364 W (rather than 1316 W), dropping our power supply’s efficiency from its rated 89% to 85%. That means the maximum continuous output power we demanded of OCZ’s Z1000 power unit was 1164 W, a full 16% beyond its rating. Bravo OCZ!
Putting power consumption on a percent scale allows us to more easily calculate relative efficiency. We based our comparison on the GTX 480 SLI configuration, where GTX 460 SLI represents the lower-energy alternative.
Putting aside special circumstances where the four-way SLI configuration took a commanding lead, its overall performance looks worse than that of three-way SLI.
Efficiency is a comparison of work done to power used, calculated by dividing the above two charts. This would have normally resulted in a 100% score for the baseline configuration.
Because there really is no such thing as 100% efficiency in the computer industry, we subtracted “1” from the results in the above chart to show only the efficiency differences. As the above chart shows, a third card uses enough energy to lose 6% in efficiency, in spite of its 29% performance gain.